Published online before print February 28, 2003, 10.1148/radiol.2271001744
(Radiology 2003;227:18.)
A more recent version of this article appeared on April 1, 2003
© RSNA, 2003
Sonography of the Scrotum1
Vikram S. Dogra, MD,
Ronald H. Gottlieb, MD,
Mayumi Oka, MD and
Deborah J. Rubens, MD
1 From the Department of Radiology, University Hospitals of Cleveland, Case Western Reserve University, 11100 Euclid Ave, Cleveland, OH 44106 (V.S.D.); and Department of Radiology, University of Rochester Medical Center, Rochester, NY (R.H.G., M.O., D.J.R.). Received November 1, 2000; revision requested December 22; final revision received February 13, 2002; accepted March 14. Address correspondence to V.S.D. (e-mail: dogra@uhrad.com).
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ABSTRACT
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Ultrasonography (US) with a high-frequency (7.5–10-MHz) transducer has become the imaging modality of choice for examination of the scrotum. US examination can provide information valuable for the differential diagnosis of a variety of disease processes involving the scrotum that have similar clinical manifestations (eg, pain, swelling, or presence of mass). The pathologic condition that may be at the origin of such symptoms can vary from testicular torsion to infection to malignancy. The ability of color and power Doppler US to demonstrate testicular perfusion aids in reaching a specific diagnosis in patients with acute scrotal pain. This review covers the anatomy of the scrotum and the scanning protocol for scrotal US, as well as detailed descriptions of disease processes and their US appearances. Newly described conditions such as intratesticular varicoceles and other benign intratesticular cystic lesions are also discussed.
© RSNA, 2003
Index terms: Orchitis, 847.201, 847.202, 847.206 • Testis, abnormalities, 847.1472, 847.1477 • Testis, cysts, 847.311 • Testis, neoplasms, 847.31, 847.32 • Testis, torsion, 847.143 • Testis, undescended, 847.1477 • Testis, US, 847.12981, 847.12983, 847.12984 • Review
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INTRODUCTION
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Ultrasonography (US) performed with a high-frequency transducer and the use of pulsed and color Doppler modes is the imaging modality of choice for evaluating acute and nonacute scrotal disease. Many of these disease processes, including testicular torsion, epididymo-orchitis, and intratesticular tumor, produce the common symptom of pain at presentation, and differentiation of these conditions and disorders is important for determining the appropriate treatment. US with a high-frequency transducer helps to better characterize intrascrotal lesions, and in many instances the findings suggest more specific diagnoses. High-frequency US in its present state can help identify certain benign intratesticular lesions, resulting in testes-sparing surgery. Familiarity with US characteristics and the examination pitfalls of scrotal US is essential for establishing the correct diagnosis and initiating treatment.
This review is organized on an organ basis and proceeds from superficial to deep structures. We review the anatomy of the scrotum and its contents, US scanning techniques, and US features of various pathologic conditions. This review is intended to bring the reader up to date with new technology and to provide insights into the US diagnosis of scrotal disorders. Newly described entities, such as intratesticular varicocele and other benign intratesticular cystic lesions, are discussed in detail.
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ANATOMY
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The scrotum is separated by a midline septum, with each half of the scrotum containing a testis and associated structures. The scrotal wall is composed of the following structures, listed from the superficial to the deep layers: rugated skin, superficial fascia, dartos muscle, external spermatic fascia, cremasteric fascia, and internal spermatic fascia. The tunica albuginea, covered by tunica vaginalis, consists of visceral and parietal layers normally separated by a few milliliters of fluid. The layer lining the scrotal wall is termed the parietal layer, and the layer extending over the testis and epididymis is referred to as the visceral layer. The parietal and visceral layers of the tunica join at the posterolateral aspect of the testis, where the tunica attaches to the scrotal wall. The tunica vaginalis covers the testis and epididymis except for a small posterior area.
Testicular size depends on age and stage of sexual development. At birth, the testis measures approximately 1.5 cm in length and 1 cm in width. Before the age of age 12 years, testicular volume is about 1–2 cm3. Clinically, a male individual is considered to have reached puberty once the testis achieves a volume of 4 cm3. The testes are symmetric ovoid structures and measure approximately 5 x 3 x 2 cm in the postpuberal male (1).
The fibrous tunica albuginea covers the testis and contains some nonstriated smooth muscle cells concentrated mostly on the posterior aspect of the testis; its function is to transport spermatozoa toward the rete testis and into the epididymis (2). The posterior surface of the tunica albuginea projects into the interior of the testis to form the incomplete septum, the mediastinum. From the mediastinum, numerous fibrous septa extend into the testis, dividing it into 250–400 lobules, each of which consists of one to three seminiferous tubules supporting the Sertoli cells and spermatocytes that give rise to sperm. These tubules contain loose interstitial tissue that contains Leydig cells, which are responsible for testosterone secretion. The seminiferous tubules open via the tubuli recti into dilated spaces called the rete testis within the mediastinum (Fig 1). The rete testis, a network of epithelium-lined spaces embedded in the fibrous stroma of the mediastinum, drains into the epididymis through 10–15 efferent ductules. The epididymis, a tubular structure consisting of a head, body, and tail, is located superior to and is contiguous with the posterior aspect of the testis. The head of the epididymis (globus major) lies cephalad to the testis and is composed of eight to 12 efferent ducts converging into a single larger duct in the body and tail (globus minor). This single duct becomes the vas deferens and continues in the spermatic cord.
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Figure 1. Diagrammatic transverse representation of the anatomy of the testis illustrates the relationships of tunica albuginea to mediastinum testis and of mediastinum testis to rete testis. The tunica vaginalis shown here is exaggerated for illustrative purposes; actually, it is a potential space.
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Four testicular appendages have been described: the appendix testis, the appendix epididymis, the vas aberrans, and the paradidymis. These are remnants of embryonic ducts (3). The appendix testis and the appendix epididymis are usually seen at scrotal US. The appendix testis (hydatid of Morgagni) is a müllerian duct remnant and consists of fibrous tissue and blood vessels within an envelope of columnar epithelium. The appendix testis is attached to the upper pole of the testis in the groove between the testis and the epididymis (Fig 2). In postmortem studies, the appendix testis has been identified in 92% of testes unilaterally and in 69% bilaterally (4). The appendix epididymis is attached to the head of the epididymis and has been encountered unilaterally in 34% and bilaterally in 12% of testes in postmortem series. The vas deferens, testicular artery, cremasteric artery, deferential artery, pampiniform plexuses, genitofemoral nerve, and lymphatic vessels compose the spermatic cord, which begins at the deep inguinal ring and descends vertically into the scrotum (5,6).
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Figure 2a. (a) Longitudinal US scan of a normal testis in a 26-year-old man shows the appendix testis (arrow) as a hypoechoic structure. The presence of hydrocele renders the appendix testis visible. (b) Longitudinal US scan of a normal epididymis in a 24-year-old man shows normal epididymis (arrow).
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Figure 2b. (a) Longitudinal US scan of a normal testis in a 26-year-old man shows the appendix testis (arrow) as a hypoechoic structure. The presence of hydrocele renders the appendix testis visible. (b) Longitudinal US scan of a normal epididymis in a 24-year-old man shows normal epididymis (arrow).
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VASCULAR SUPPLY
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The right and left testicular arteries, branches of the abdominal aorta, arise just distal to the renal arteries and provide the primary vascular supply to the testes. They enter the spermatic cord at the deep inguinal ring and continue along the posterior surface of the testis, penetrating the tunica albuginea where the capsular arteries form and course through the tunica vasculosa, located beneath the tunica albuginea. Centripetal branches arising from the capsular arteries carry blood toward the mediastinum, where they divide to form the recurrent rami that carry blood away from the mediastinum into the testis. A transmediastinal arterial branch of the testicular artery is present in approximately one-half of normal testes (7) (Fig 3); it courses through the mediastinum to supply the capsular arteries and is usually accompanied by a large vein. The deferential artery, a branch of the superior vesicle artery, and the cremasteric artery, a branch of the inferior epigastric artery, supply the epididymis, vas deferens, and peritesticular tissue (8).
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Figure 3. Transverse US scan of the testis shows a normal transmediastinal artery (arrow) as a linear hypoechoic band. Color Doppler flow US (not shown) revealed flow through the vessel.
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The number and locations of anastomoses vary between the testicular artery and its branches and between the artery to the vas deferens and the cremasteric artery. Branches of the pudendal artery supply the scrotal wall (9). Venous drainage is via the pampiniform plexus of draining veins, which is formed around the upper half of the epididymis in a variable fashion and continues as the testicular vein through the deep inguinal ring. The right testicular vein empties into the inferior vena cava, and the left testicular vein empties into the left renal vein (10).
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US EVALUATION
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Scanning Protocol
Scrotal US is performed with the patient in the supine position and the scrotum supported by a towel placed between the thighs. Optimal results are obtained with a 7–10-MHz high-frequency linear-array transducer. Scanning is performed most often with the transducer in direct contact with the skin, but if necessary a stand-off pad can be used for evaluation of superficial lesions.
The testes are examined in at least two planes, along the long and transverse axes. The size and echogenicity of each testis and the epididymis are compared with those on the opposite side. Scrotal skin thickness is evaluated. Color Doppler and pulsed Doppler parameters are optimized to display low-flow velocities, to demonstrate blood flow in the testes and surrounding scrotal structures. Power Doppler US may also be used to demonstrate intratesticular flow in patients with an acute scrotum. In patients being evaluated for an acute scrotum, the asymptomatic side should be scanned initially in order to set the gray-scale and color Doppler gain settings to allow comparison with the affected side. Transverse images with portions of each testis on the same image should be acquired in gray-scale and color Doppler modes. The structures within the scrotal sac are examined to detect extratesticular masses or other abnormalities. In patients with small palpable nodules, scans should include the area of clinical concern. A finger should be placed beneath the nodule and the transducer placed directly over the nodule for scanning, or a finger can be placed on the nodule and the transducer opposite to confirm imaging of the lesion. Additional techniques such as use of the Valsalva maneuver or upright positioning can be used as needed for venous evaluation.
US Anatomy
The normal scrotal wall thickness is approximately 2–8 mm, depending on the state of contraction of the cremasteric muscle (11).
Prepubertal testes are of low to medium echogenicity, whereas pubertal and postpubertal testes are of medium homogeneous echogenicity, reflecting the development of germ cell elements and tubular maturation (12). The mediastinum testis is identified as an echogenic band of variable thickness and length extending in a caudocranial direction (Fig 4). The normal rete testis can be identified at high-frequency US in 18% of patients as a hypoechoic area with a striated configuration adjacent to the mediastinum testis (as opposed to the tubular ectasia of the rete testis when it is seen as fluid-filled dilated tubular structures) (13,14). The tunica albuginea can be seen as a thin echogenic line around the testis. The space between the two leaves of the tunica vaginalis normally contains small amounts of fluid, seen as a thin echo-free rim in the area adjacent to the head of the epididymis. This normal amount of fluid should not be misinterpreted as hydrocele. The epididymis is best evaluated in a longitudinal view when the epididymal head (globus major) can be seen as a pyramidal structure 5–12 mm in maximum length lying atop the superior pole of the testis. The head of the epididymis is usually isoechoic to the testis, and its echotexture may be coarser than that of the testis (13,15). The narrow body of the epididymis (2–4 mm in diameter), when normal, is usually indistinguishable from the surrounding peritesticular tissue. The tail of the epididymis (globus minor) is approximately 2–5 mm in diameter and can be seen as a curved structure at the inferior pole of the testis, where it becomes the proximal portion of the ductus deferens.
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Figure 4. Normal testis in a 24-year-old man. Mediastinum testis (arrow) is a normal finding, seen as an echogenic band running across the testis on a sagittal US scan.
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The otherwise normal appendix testis and the appendix epididymis are typically seen only when a hydrocele is present. The appendix testis appears as an ovoid structure 5 mm in length in the groove between the testis and the epididymis. The appendix testis is isoechoic to the testis and may occasionally be cystic. The appendix epididymis is of the same approximate dimensions as the appendix testis but is more often pedunculated (11).
Testicular perfusion can be evaluated with color Doppler, power Doppler, and spectral Doppler US. Color Doppler US can reliably demonstrate intratesticular flow (12,16,17). Power Doppler US uses the integrated power of the Doppler signal to depict the presence of blood flow. Higher power gains are more likely with power Doppler US than with standard color Doppler US, resulting in increased sensitivity for detection of blood flow. Power Doppler scanning is valuable in scrotal US because of its increased sensitivity to low-flow states and its independence from Doppler angle correction (18,19). Pulsed Doppler US is a useful method for identification of flow in the testes with use of the time-velocity spectrum to quantify blood flow (20). The spectral waveform of the intratesticular arteries characteristically has a low-resistance pattern (16), with a mean resistive index of 0.62 (range, 0.48–0.75) (12); however, this is not true for a testicular volume of less than 4 cm3, as is often found in prepubertal boys, when diastolic arterial flow may not be detectable (21). In one report, the spectral waveform in the epididymis was described as having a low-flow, high-resistance pattern (16); however, that has not been the experience of other researchers (22). The resistive index of a normal epididymis ranges from 0.46 to 0.68, and color Doppler US can demonstrate blood flow in a normal epididymis (23).
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SCROTAL WALL LESIONS
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Noninflammatory Causes
Noninflammatory causes of scrotal wall swelling include heart failure, idiopathic lymphedema, liver failure, and lymphatic and venous obstruction. The scrotal wall appears thickened, with layers of alternating hypoechogenicity and hyperechogenicity, called the onion-ring appearance (24). Epidermoid cysts of the scrotal wall have been described.
Inflammatory Causes
Cellulitis.—Scrotal wall cellulitis is common in patients who are obese, diabetic, or immunocompromised. The US signs are an increase in scrotal wall thickness and the presence of hypoechoic areas with increased blood flow seen at color Doppler US. Scrotal wall cellulitis may lead to scrotal abscess. Such abscesses are usually well loculated, with irregular walls and low-level internal echoes.
Fournier gangrene.—Fournier gangrene is a polymicrobial necrotizing fasciitis of the scrotum that frequently extends to the lower abdominal wall. The most common pathogens isolated in patients with this syndrome are Klebsiella, Proteus, Streptococcus, Staphylococcus, Peptostreptococcus, Escherichia coli, and Clostridium perfringens (25–27). Fournier gangrene constitutes a urologic emergency for which early recognition is demanded because of its high mortality rate—reportedly as high as 75%. The diagnosis of Fournier gangrene is based primarily on clinical examination results rather than on imaging findings. When clinical findings are ambiguous, however, diagnostic imaging is useful.
Current imaging techniques for the initial evaluation for Fournier gangrene include conventional radiography, US, and computed tomography (CT) (28). Crepitus (gas in the tissue) has been reported in 18%–62% of these cases and can be detected by using US, CT, and conventional radiography. Subcutaneous gas within the scrotal wall is the US hallmark of Fournier gangrene. At US, the gas appears as numerous, discrete, hyperechoic foci with reverberation artifacts (28,29) (Fig 5). Other US findings include scrotal wall thickening, with the echotexture of the testes and epididymis remaining normal. The only other condition manifesting with gas at US examination is an inguinoscrotal hernia. This can be differentiated from Fournier gangrene by the presence of gas within the protruding bowel lumen and away from the scrotal wall. CT and conventional radiography can also aid in determining the location and cause of gas in the scrotum.
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Figure 5. Surgically proved Fournier gangrene in a 38-year-old man. Longitudinal US scan of the testis (arrowhead) shows sparing of the testis in Fournier gangrene. Both sonograms show scrotal wall thickening (open arrows) and air (long arrow) parallel to the transducer face, with reverberation artifacts (short solid arrows).
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Scrotal Wall Malignant Lesions
Extratesticular primary solid neoplasms are extremely rare, and metastatic disease to the scrotal wall occurs even less frequently. Only sporadic cases, such as cases of metastatic melanoma, anal carcinoma, and lung carcinoma, have been reported (30–32). Most of these metastatic lesions are hypoechoic but can have variable echogenicity. The main differential consideration is tumor arising from the epididymis and tunicae of the spermatic cord.
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INGUINAL AND SCROTAL SWELLING
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Inguinal Hernia
Clinical history and physical examination results are usually sufficient to enable diagnosis of an intrascrotal inguinal hernia. US is helpful in patients with equivocal physical findings and in those presenting with acute inguinoscrotal swelling. Hernias are classified as direct or indirect, depending on their relationship to the inferior epigastric artery. Korenkov et al (33) were able to demonstrate the inferior epigastric artery in 100% of their cases of small inguinal hernia by using color Doppler US. The hernial sac most commonly contains bowel, while its next most common contents are omentum. Rare contents include other abdominal organs, such as Meckel diverticulum, urinary bladder, and others. Gray-scale US findings include a fluid- or air-filled loop of bowel in the scrotum. The presence of real-time peristalsis is diagnostic for the presence of bowel. Occasionally, because contraction of the dartos can also mimic peristalsis at real-time US, the examiner should be aware of this possibility to prevent misdiagnosis. If the omentum has herniated, hyperechoic areas are present and correspond to omental fat.
Bowel strangulation is more common in indirect than in direct inguinal hernia. An akinetic dilated loop of bowel observed at US in the hernial sac is reported (34) to have high sensitivity (90%) and specificity (93%) for the recognition of bowel strangulation. Hyperemia of scrotal soft tissue and bowel wall are suggestive of strangulation (12). Patients with Richter hernia, a strangulated hernia in which only a portion of the circumference of the bowel is obstructed (35), usually present with gastroenteritis. Such cases can pose a diagnostic challenge because of the small size of the hernia and the eccentric bowel wall involvement with limited luminal compromise. This hernia commonly occurs at a femoral site. It is important to recognize this condition because preoperative delays in diagnosis and high postoperative morbidity are very common compared with those associated with other types of strangulated hernias (36).
Hydrocele, Hematocele, and Pyocele
The normal scrotum contains a few milliliters of serous fluid between the layers of the tunica vaginalis. Approximately 85% of asymptomatic men in a series of 40 volunteers who underwent scrotal US had minimal amounts of fluid in one hemiscrotum but no hydrocele (37). A hydrocele is an abnormally large collection of serous fluid and is the most common cause of painless scrotal swelling (38). A hydrocele may develop for a variety of reasons, including trauma, infection, testicular torsion, or tumor, or it may be idiopathic. Congenital hydroceles result from a patent processus vaginalis that permits entry of peritoneal fluid into the scrotal sac. In adults, hydroceles are usually associated with an intrascrotal pathologic condition, which should be determined and treated. Hydroceles are anechoic fluid collections with good sound transmission; they surround the anterolateral aspects of the testis. Hydroceles may occasionally manifest low-level echoes secondary to high protein or cholesterol content (39,40).
Hematoceles and pyoceles are rare. A hematocele is usually secondary to trauma, surgery, or neoplasm. A pyocele results from untreated epididymo-orchitis or rupture of an intratesticular abscess into the space between the layers of the tunica vaginalis. Both conditions appear at US as complex cystic lesions with internal septations and loculations. Skin thickening and calcifications can be seen in chronic cases.
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CONDITIONS OF THE SPERMATIC CORD
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Varicocele
Varicoceles (idiopathic or primary) are present in approximately 15% of adult men (41). Patients with idiopathic varicoceles usually present between the ages of 15 and 25 years. A varicocele is an abnormal dilatation of the veins of the spermatic cord and is usually caused by incompetent valves in the internal spermatic vein. This results in impaired drainage of blood into the spermatic cord veins when the patient assumes an upright position or during a Valsalva maneuver (42). The veins of the pampiniform plexus normally range from 0.5 to 1.5 mm in diameter, with the main draining vein being as large as 2 mm in diameter. Varicoceles are more common on the left side for the following reasons: (a) The left testicular vein is longer; (b) the left testicular vein enters the left renal vein at a right angle; (c) the left testicular artery in some men arches over the left renal vein, thereby compressing it; and (d) the descending colon distended with feces may compress the left testicular vein (43).
Palpation reveals a scrotal mass that may feel like a bag of worms, with or without a palpable thrill. In one study, all patients with palpable varicoceles had a spermatic vein diameter of 5–6 mm (44). Approximately one-third of men undergoing evaluation for infertility present with varicocele; however, not all patients with infertility have a palpable varicocele. In a study of 1,372 infertile men (45), varicocele was found at US in 29% of patients; of these, only 60% had a palpable varicocele. Diagnosis of palpable varicocele is important, because treatment improves sperm quality in as many as 53% of the cases. The relationship between nonpalpable (subclinical) varicocele and infertility remains controversial.
US should be performed with the patient in both a supine and a standing position. The US appearance of varicocele consists of multiple, hypoechoic, serpiginous, tubular structures of varying sizes larger than 2 mm in diameter that are usually best visualized superior and/ or lateral to the testis. When large, a varicocele can extend posteriorly and inferiorly to the testis. Occasionally, low-level internal echoes can be detected in these dilated veins, secondary to slow flow. Color flow and duplex Doppler US optimized for low-flow velocities help confirm the venous flow pattern, with phasic variation and retrograde filling during a Valsalva maneuver. The sensitivity and specificity of varicocele detection approaches 100% with color Doppler US.
Secondary varicoceles result from increased pressure on the spermatic vein produced by disease processes such as hydronephrosis, cirrhosis, or abdominal neoplasm (Fig 6). Neoplasm is the most likely cause of nondecompressible varicocele in men over 40 years of age; it is classically caused by a left renal malignancy invading the renal vein (15). Noncompressible varicoceles on the left or right should prompt evaluation of the retroperitoneum to exclude retroperitoneal mass and of the left renal vein for thrombus or tumor extension.
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Figure 6a. Surgically confirmed secondary left varicocele in a 60-year-old man. (a) Contrast material-enhanced transverse CT scan and (b) transverse US scan of the left testis (t) reveal large left renal cell carcinoma invading the left renal vein (arrow in a), resulting in secondary varicocele (arrow in b). (Image courtesy of Patrick Fultz, MD, Rochester, NY.)
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Figure 6b. Surgically confirmed secondary left varicocele in a 60-year-old man. (a) Contrast material-enhanced transverse CT scan and (b) transverse US scan of the left testis (t) reveal large left renal cell carcinoma invading the left renal vein (arrow in a), resulting in secondary varicocele (arrow in b). (Image courtesy of Patrick Fultz, MD, Rochester, NY.)
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Tumors of the Spermatic Cord
Most benign tumors of the spermatic cord are lipomas. Malignant neoplasms account for approximately 25% of neoplasms of the paratesticular tissues, and the majority of these are sarcomas. Rhabdomyoma and sarcoma are the most common tumors, accounting for 40% of both benign and malignant paratesticular tumors. They occur predominantly in infants and in children; adults are rarely affected. At the time of presentation, the tumor is a large intrascrotal mass with a diameter of up to 20 cm. At gross specimen examination, the mass is solid, firm, rarely hemorrhagic, and grayish white. Despite frequent retroperitoneal lymph node involvement, the 5-year survival rate is 75% (46). Tumors of smooth muscle origin are the second most common tumor of this region, occurring in patients aged 40–70 years; 70% are leiomyomas, and 30% are leiomyosarcomas. Other malignant tumors of the spermatic cord include liposarcoma, fibrosarcoma, myxochondrosarcoma, and malignant fibrous histiocytoma (47).
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EPIDIDYMIS
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Epididymo-orchitis
Epididymo-orchitis and epididymitis are common causes of acute scrotal pain in adolescent boys and adults. At physical examination early in the course of the disease, the epididymis can be palpated as an enlarged tender structure separate from the testis. Clinically, scrotal pain associated with epididymitis is usually relieved when the testes are elevated over the symphysis pubis (the Prehn sign) (48). This sign may help clinically differentiate between epididymitis and torsion of the spermatic cord, in which scrotal pain is not lessened with this maneuver. In adolescents, many instances are secondary to sexually transmitted organisms such as Chlamydia trachomatis and Neisseria gonorrhoeae. In prepubertal boys and in men over 35 years of age, the disease is most frequently caused by E coli and Proteus mirabilis (49). US evaluation in patients with scrotal trauma may show epididymal enlargement and hyperemia, which should not be confused with infectious epididymitis (50). Rare causes such as sarcoidosis (51), brucellosis (52), tuberculosis, cryptococcus, and mumps may also cause epididymitis and orchitis. Drugs such as amiodarone hydrochloride may also cause epididymitis (chemical epididymitis) (2). Complications of acute epididymitis include chronic pain, infarction, abscess, gangrene, infertility, atrophy, and pyocele.
Gray-scale US findings of acute epididymitis include an enlarged hypoechoic or hyperechoic (presumably secondary to hemorrhage) epididymis (12). Indirect signs of inflammation, such as reactive hydrocele or pyocele with scrotal wall thickening, are present in most cases. The epididymis is the organ primarily involved in epididymo-orchitis, with orchitis developing in 20%–40% of cases due to direct spread of infection. Diffuse testicular involvement is confirmed by the presence of testicular enlargement and an inhomogeneous testicular echotexture. Gray-scale US findings are nonspecific, but acute epididymo-orchitis is the most common disorder with this combination of findings. Farriol et al (53) reported 11 of 20 cases with enlargement and heterogeneous echogenicity of the epididymis, testes, or both in inflammatory scrotal diseases. Orchitis is characterized by edema of the testes contained within a rigid tunica albuginea, resulting in heterogeneous echogenicity (54). The process may be seen as diffuse or focal, with the latter manifesting as multiple hypoechoic lesions within the testicular parenchyma.
Heterogeneous echogenicity does not always indicate orchitis. Leukemia and lymphoma of the testis have a similar appearance and are often (but not always) bilateral, whereas infection (excluding mumps) is usually unilateral. It is difficult to differentiate focal areas of heterogeneous echogenicity from neoplastic lesions solely on the basis of gray-scale US findings. Because this pattern is not pathognomonic of orchitis when the testes show heterogeneous echogenicity, the condition should be followed to complete resolution and documented with US to rule out tumor, infarction, and metastasis (Fig 7).
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Figure 7. Clinically proved acute epididymo-orchitis in a 32-year-old man. Transverse US scan of testis shows acute epididymo-orchitis as focal areas of decreased echogenicity (arrowhead) in testicular parenchyma (T), resembling a metastatic lesion with reactive hydrocele (F). These hypoechoic areas were completely resolved at follow-up US after 2 weeks of antibiotic treatment.
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At color and power Doppler US, the hallmark of scrotal infection is hyperemia of the epididymis, testis, or both (Fig 8). Increased blood flow to the epididymis and testis at color Doppler US examination is a well-established criterion for the diagnosis of epididymo-orchitis (55). The sensitivity of color Doppler US imaging in detecting scrotal inflammation is nearly 100% (56,57). In 20% of cases of epididymitis and 40% of cases of orchitis, hyperemia is the diagnostic color Doppler US finding, because gray-scale US findings are normal. In acute epididymitis, there are an increased number and concentration of identifiable vessels with hyperemia, resulting in a high-flow, low-resistance pattern (56,58). Analysis of the spectral waveform and resistive index can also provide useful information, because inflammation of the epididymis and testis is associated with decreased vascular resistance compared with that seen in healthy individuals. However, it should be noted that performance of resistive index measurements on the epididymis is not a standard US procedure. In the testes of a healthy volunteer, the resistive index is rarely less than 0.5, but in more than half of patients with epididymo-orchitis, the resistive index is less than 0.5 (22). Use of a peak systolic velocity threshold of 15 cm/sec results in a diagnostic accuracy of 90% for orchitis and 93% for epididymitis (59). Reversal of flow during diastole in acute epididymo-orchitis is suggestive of venous infarction (60).
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Figure 8. Clinically proved acute epididymitis in a 21-year-old man. Left: Transverse US scan of right testis and epididymis shows an enlarged hypoechoic epididymis (arrow). Right: Transverse color Doppler US scan of same epididymis demonstrates increased vascularity (arrow). The testis is normal.
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Chronic Epididymitis
This condition is characterized by persistent pain in the scrotal area (61). At gray-scale US, it is characterized by an enlarged epididymis and increased echogenicity (62). There may be calcifications within the epididymis. Granulomatous epididymo-orchitis can be seen in cases of tuberculosis, brucellosis, sarcoidosis, leprosy, and syphilis. In one study in which 22 patients with granulomatous epididymo-orchitis of tuberculous origin were evaluated (63), the epididymis was hypoechoic in 13 patients, had mixed echogenicity in seven patients, and was hyperechoic in two patients.
Sperm Granuloma
Sperm granuloma, or epididymitis nodosa, a type of chronic epididymitis, occurs secondary to inflammation, trauma, and vasectomy. Sperm granuloma, a granulomatous reaction to extravasated sperm cells, occurs after vasectomy in up to 40% of patients, but only 3% of these patients experience pain (64). At US, sperm granuloma appears as a well-demarcated hypoechoic intraepididymal lesion. Other US findings include epididymal enlargement, cystic changes, and inhomogeneous echotexture (65).
Epididymal Tumors
Spermatocele and epididymal cyst.—Extratesticular cysts are more common than intratesticular cysts. Extratesticular cysts can be found in the spermatic cord, epididymis, tunica albuginea, or tunica vaginalis. Spermatocele, a common type of extratesticular cyst, represents cystic dilatation of tubules of the efferent ductules in the head of the epididymis (11). Spermatoceles are usually unilocular but can be multilocular and may be associated with a prior vasectomy. At US examination, they are well-defined hypoechoic lesions usually measuring 1–2 cm and demonstrating posterior acoustic enhancement. They often contain low-level echogenic proteinaceous fluid and spermatozoa (66).
Epididymal cysts are less common than spermatoceles and are indistinguishable from the latter at US. Epididymal cysts contain clear serous fluid and may arise throughout the epididymis, while spermatoceles almost always arise in the epididymal head. An increased incidence of epididymal cysts has been reported in boys who are exposed in utero to diethylstilbestrol. Although epididymal head cysts cannot be differentiated from spermatoceles, they usually are not clinically relevant.
Adenomatoid tumors.—Paratesticular tumors are rare, with adenomatoid tumors constituting 30% of these tumors; they are most likely of mesothelial origin. The majority of reported cases involve the epididymis (Fig 9). Patient age at the time of presentation ranges from 18 to 79 years (47). Adenomatoid tumors are usually found incidentally by the patient or by a physician at physical examination. Characterized as a painless firm scrotal mass, an adenomatoid tumor is a benign neoplasm with no reported metastases or recurrence after excision (67). The US appearance varies from hypoechoic to hyperechoic to isoechoic, compared with adjacent tissues.
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Figure 9. Surgically proved adenomatoid tumor in the left hemiscrotum of a 42-year-old man. Transverse US scan of left testis shows a heterogeneous extratesticular mass (arrow) measuring 2.75 x 2.49 cm in the inferomedial portion of the testis. At surgery, the tumor was found to arise from the tail of the epididymis.
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Papillary cystadenoma and other rare epididymal tumors.—Papillary cystadenoma of the epididymis is a rare benign tumor often associated with von Hippel–Lindau disease. Up to 60% of men with von Hippel–Lindau disease have this lesion, which causes minimal or no discomfort. The US appearance ranges from a primary cystic mass with an intramural solid component to an almost completely solid mass. In a recent study in 56 men with von Hippel–Lindau disease (68), US revealed a unilateral or bilateral solid abnormality in the head of the epididymis in 30 (54%) patients. A solid mass ranging from 1.5 to 2 cm was the most frequent finding.
Other rare tumors of the epididymis include leiomyoma, lipoma, rhabdomyoma, lymphoma, and lymphangioma (69). Leiomyoma of the epididymis is a rare benign neoplasm with only one-tenth the occurrence rate of rare adenomatoid tumor. Approximately 25% of solid tumors of the epididymis are malignant, and the majority are metastases from a tumor at another site. Primary adenocarcinomas of the epididymis are very rare (70). Serous papillary carcinomas have also been reported (71).
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CONDITIONS OF THE TESTES
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Testicular Torsion
US plays an important role in helping differentiate acute epididymo-orchitis from testicular torsion, which is a surgical emergency. Both manifest with acute pain and swelling. Clinical differentiation of these conditions is difficult, with a false-positive rate of nearly 50% for diagnosis of testicular torsion based on clinical findings alone, which therefore often results in unnecessary surgical exploration (72).
In 1776, Hunter provided the first description of testicular torsion (48). The chances of torsion of the testis or its appendage developing by the age of 25 years is about one in 160 (73). Testicular torsion can occur at any age; however, it is most frequent in adolescent boys. In testicular torsion, venous obstruction occurs first, followed by obstruction of arterial flow and ultimately by testicular ischemia. The extent of testicular ischemia depends on the degree of torsion, which ranges from 180° to 720° or greater. The testicular salvage rate depends on the degree of torsion and the duration of ischemia. A nearly 100% salvage rate exists within the first 6 hours after the onset of symptoms; a 70% rate, within 6–12 hours; and a 20% rate, within 12–24 hours (74).
Two types of torsion have been described: extravaginal and intravaginal. Extravaginal testicular torsion occurs exclusively in newborns. Torsion occurs outside the tunica vaginalis when the testes and gubernacula are not fixed and are free to rotate (75). The affected neonate presents with swelling, discoloration of the scrotum on the affected side, and a firm painless mass in the scrotum (76,77). The testis is typically infarcted and necrotic at birth. US findings include an enlarged heterogeneous testis, ipsilateral hydrocele, skin thickening, and no color Doppler flow signal in the testis or spermatic cord (78). In children, power Doppler US is more sensitive than color Doppler US for detection of intratesticular blood flow. In one study (79), power Doppler US demonstrated intratesticular blood flow in 66 (97%) of 68 testes, while color Doppler US demonstrated intratesticular blood flow in 60 (88%) testes; both techniques combined depicted blood flow in all 68 (100%) testes. Color Doppler US and scintigraphy are comparable with regard to diagnosis of torsion in adolescent and adult populations (56,57). Scintigraphy remains a reasonable alternative for evaluation of acute scrotal pain and should be used when color Doppler US sensitivity for low-velocity, low-volume testicular blood flow is inadequate and the diagnosis of torsion remains in question.
Intravaginal torsion occurs within the tunica vaginalis. The predisposing factors include a long and narrow mesentery or a bell-clapper deformity, in which the tunica vaginalis completely encircles the epididymis, distal spermatic cord, and testis rather than attaches to the posterolateral aspect of the testis. The deformity leaves the testis free to swing and rotate within the tunica vaginalis much like a clapper inside a bell. The bell-clapper deformity is bilateral in most cases. A 12% prevalence of bell-clapper deformity was found in one autopsy series (80), suggesting that it is a more common deformity than intravaginal testicular torsion.
Patients with acute torsion present after a sudden onset of pain followed by nausea, vomiting, and a low-grade fever. Physical examination reveals a swollen, tender, and inflamed hemiscrotum. The cremasteric reflex is usually absent (81), and the pain cannot be relieved by elevating the scrotum (48).
US is considered the first step in evaluation. The role of color Doppler and power Doppler US in the diagnosis of acute testicular torsion is well established (17,55,57). By using the absence of identifiable intratesticular flow as the only criterion for detecting testicular torsion, color Doppler US was 86% sensitive, 100% specific, and 97% accurate in the diagnosis of torsion and ischemia in painful scrotum (56) (Fig 10). The high degree of accuracy is due to the superiority of power Doppler US depiction of intratesticular vessels, compared with that of color Doppler US, in normal prepubertal and postpubertal testes (82).
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Figure 10. Surgically proved testicular torsion in a 20-year-old man. Longitudinal color Doppler US scan shows an enlarged hypoechoic testis (arrow) with no intratesticular blood flow. Increased paratesticular flow (arrowhead) is secondary to hyperemia.
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US findings vary with the duration and degree of rotation of the spermatic cord. Gray-scale images are nonspecific for testicular torsion (58) and often appear normal if the torsion has just occurred. Testicular swelling and decreased echogenicity are the most commonly encountered findings 4–6 hours after the onset of torsion. At 24 hours after onset, the testis has a heterogeneous echotexture secondary to vascular congestion, hemorrhage, and infarction; this condition is referred to as late or missed torsion. An enlarged hypoechoic epididymal head may be visible because the deferential artery supplying the epididymis is often involved in the torsion (83). In a recent prospective study (84), a spiral twisting of the spermatic cord at the external inguinal ring was seen in 14 of 23 cases of torsion. The twisting induced an abrupt change in the course, size, and shape of the spermatic cord below the point of torsion and appeared as a round or oval homogeneous extratesticular mass with or without blood flow that could be traced cephalad to the normal spermatic cord. In the setting of testicular torsion, normal testicular echogenicity is a strong predictor of testicular viability (85). Other indicators include the presence of scrotal wall thickening and reactive hydrocele.
Because gray-scale US findings are often normal in the early phases of torsion, the Doppler component of the examination is essential. The absence of testicular flow at color and power Doppler US is considered diagnostic of ischemia, provided that the scanner is optimized for detection of slow flow, is limited to the use of a small color-sampling box, and is adjusted for the lowest repetition frequency and the lowest possible threshold setting (86). The threshold should be set just above the level for detection of color noise.
Torsion is not an all-or-none phenomenon but may be complete, incomplete, or transient. Cases of partial or transient torsion present a diagnostic challenge. The ability of color Doppler US imaging to enable accurate diagnosis of incomplete torsion remains undetermined. The role of spectral Doppler US analysis is not well established with regard to diagnosis of partial torsion, but the findings may be useful (87). To our knowledge, there are no studies available that validate the role of spectral Doppler US in partial torsion; however, findings from sporadic case reports (88,89) exist that suggest its usefulness. Asymmetry in resistive indices, with decreased diastolic flow or diastolic flow reversal, may be seen. The presence of color or power Doppler signal in a patient with the clinical manifestation of torsion does not exclude torsion (89).
Patients with torsion of the appendix testis and appendix epididymis present with acute scrotal pain, but there are usually no other physical symptoms, and the cremasteric reflex can still be elicited. The classic finding at physical examination is a small firm nodule that is palpable on the superior aspect of the testis and exhibits bluish discoloration through the overlying skin; this is called the "blue dot" sign (90). Approximately 91%–95% of twisted testicular appendices involve the appendix testis and occur most often in boys 7–14 years old.
US evaluation of torsion of the appendages of the testes usually reveals a hyperechoic mass with a central hypoechoic area adjacent to the testis or epididymis (91–93). Reactive hydrocele and skin thickening are common in these cases. Increased peripheral flow may be seen around the twisted testicular appendage at color Doppler US (17,49,56,91). These cases are managed conservatively, with attention to pain management. The pain usually resolves in 2–3 days, with atrophy of the appendix, which may calcify. The role of US examination in torsion of testicular appendages is to exclude testicular torsion and acute epididymo-orchitis.
Primary Orchitis
Primary orchitis in isolation is rare and most commonly caused by mumps. Bilateral involvement is seen in 14%–35% of cases, and the affected testes appear enlarged with decreased echogenicity. In one study (94) of mumps-related epididymo-orchitis, nine of 11 cases were unilateral, and in all 11 cases enlarged testes and increased testicular vascularity were present. Testicular echogenicity was uniformly decreased in all 11 cases (94). Hyperemia and heterogeneity isolated to the testis can be seen in cases of orchitis, tumor, infarction, and especially in transient torsion of the testis. Because intratesticular venous flow is difficult to detect in normal testes, increased and easily detected venous flow in the testes is highly suggestive of orchitis (95).
Nonpalpable Testis
A testis may be nonpalpable because it is congenitally absent, cryptorchid, atrophic, retractile, or ectopic. Cryptorchism is defined as complete or partial failure of the intraabdominal testes to descend into the scrotal sac. The undescended testis may be positioned anywhere along the normal path of descent. The most common location is in the inguinal canal (72%), followed by prescrotal (20%) and abdominal (8%) locations (96). The undescended testis is generally smaller and less echogenic than the normal testis (Fig 11). The ectopic testis may lie in the perineum, femoral canal, superficial inguinal pouch, or contralateral hemiscrotum. The most common ectopic location is in the superficial inguinal pouch, a subcutaneous pocket in front of and lateral to the external ring (97,98).
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Figure 11. Bilateral undescended testes in a 36-year-old man. Longitudinal US scan of the right testis at the level of the inguinal canal reveals an oval-shaped testis, which is hypoechoic relative to surrounding structures (arrow). Left testis is not shown.
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The major complications of cryptorchism are malignant degeneration, infertility, torsion, and bowel incarceration because of an associated indirect inguinal hernia. Although early clinical investigators estimated the rate of testicular cancer in patients with cryptorchism to be as much as 50 times greater than that in the rest of the population, more recent epidemiologic studies indicate a risk ratio of 2.5 to 8 (99). Seminoma is the most common malignancy in the cryptorchid testis. Orchiopexy of cryptorchid testis is usually performed in patients between 1 and 10 years of age; orchiectomy is considered for postpubertal patients. Orchiopexy does not change the risk of malignant degeneration of the once cryptorchid testis, but it does allow easier surveillance. If seminoma does occur in one testis, prompting unilateral orchiectomy, the remaining testis remains at a higher risk for the development of cancer.
Testicular Calcification
Testicular microlithiasis.—Testicular microlithiasis (TM) is an uncommon condition usually discovered incidentally at US. It is characterized by intratubular calcifications within a multilayered envelope containing organelles, vesicles, and collagen fibers. TM appears at US as multiple echogenic foci with no acoustic shadowing. The multilayered envelope, composed of stratified collagen fibers, is presumed to be responsible for the absence of acoustic shadowing (100,101); however, this absence could also be attributable to calcifications too small to produce shadowing. Although minor microcalcification within a testis is considered normal, the typical US appearance of TM is of multiple nonshadowing echogenic foci measuring 2–3 mm and randomly scattered throughout the testicular parenchyma (102,103) (Fig 12). The presence of five or more foci per transducer field in one testis is abnormal (15).
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Figure 12. Surgically proved germ cell tumor in a 34-year-old man. Sagittal US scan of left testis shows multiple microliths (straight arrow) and a hypoechoic focal lesion (curved arrow, cursors), which was determined to be a germ cell tumor.
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Intratubular germ cell neoplasia (IGCN) has been associated with a high rate of malignancy (IGCN is a pathologic diagnosis). Approximately 50% of patients with IGCN develop primary testicular cancer within 5 years (104). Sixty-seven percent of patients with IGCN also have TM (13). The percentage of patients with TM who develop IGCN is unknown (100). TM is generally a bilateral condition, except in cases of cryptorchism. TM has been associated with testicular neoplasia in 18%–75% of cases (105). The exact prevalence of testicular tumors associated with TM is unknown. Currently, there is no evidence that TM is either a premalignant condition or a causative agent in testicular neoplasia; however, in view of its reported associations with testicular neoplasia, annual US follow-up is recommended for at least several years after the diagnosis (105). Other associations of TM with cryptorchism, infertility, male pseudohermaphroditism, Klinefelter syndrome, and pulmonary alveolar microlithiasis have been reported. The incidence of testicular malignancy is increased in patients with cryptorchism, infertility, and male pseudohermaphroditism (106).
Macrocalcifications.—Macrocalcifications can be intra- or extratesticular. Calcifications in the epididymis can occur secondary to inflammatory conditions such as tuberculosis or trauma. Scrotoliths (scrotal pearls) are calcified bodies within the scrotum that have no clinical importance (58). They may represent a loose body caused by torsion of the appendix testis or epididymis (54). The presence of a small quantity of fluid around the testis at US examination facilitates the diagnosis of scrotoliths (Fig 13). Intratesticular macrocalcifications raise the suspicion of large cell calcifying Sertoli cell tumor, burned-out germ cell tumor, or posttraumatic change.
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Figure 13. Scrotoliths (scrotal pearls) in a 30-year-old man. Transverse US scan of testes shows extratesticular echogenic foci (arrow) with posterior acoustic shadowing. There is minimal fluid in the tunica vaginalis (arrowhead).
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Benign Testicular Lesions
US is the modality of choice for characterizing palpable testicular lesions. Benign extratesticular lesions are more common than benign intratesticular lesions. Most intratesticular tumors are malignant; however, benign intratesticular lesions do exist. The majority of intratesticular cystic lesions are benign, and recognition of this can prevent unnecessary surgical exploration.
Cysts of the tunica albuginea.—The etiology of cysts of the tunica albuginea is unknown, but these cysts are believed to be mesothelial in origin. The cysts range from 2–5 mm in size and are often detected only when a patient presents with a palpable mass (107). They can be unilocular or multilocular. They sometimes calcify, and all that remains is the palpable calcification, which casts an acoustic shadow.
Simple cysts.—Usually detected incidentally and most often occurring in men at least 40 years of age, simple cysts vary in size from 2 mm to 2 cm. These cysts are usually solitary but can also be multiple. They are located adjacent to the mediastinum testis and are associated with extratesticular spermatoceles. At US, they appear with an anechoic center and through-transmission and without a perceptible wall (108). Suspected causes of intratesticular cysts include trauma, surgery, and prior inflammation. They do not require treatment.
Epidermoid cyst.—Ranging in size from 1 to 3 cm, epidermoid cysts are uncommon benign tumors of germ cell origin and are also known as keratocysts. They are nontender and may be palpable. The patient’s age at presentation is variable but commonly ranges from 20 to 40 years (109). The US appearance of epidermoid cyst varies with the maturation, compactness, and quantity of keratin within the cyst. Four US appearances have been described: (a) a target appearance—a halo with a central area of increased echogenicity, (b) a sharply defined mass with a rim of calcification, (c) a solid mass with an echogenic rim, and (d) the classic appearance of an "onion-ring" pattern with alternating hyperechoic and hypoechoic layers (Fig 14). This onion-ring pattern is considered characteristic of an epidermoid cyst and corresponds to its natural evolution (110,111). Color flow or pulsed Doppler US examination demonstrates no blood flow within the cyst. The combination of an onion-ring configuration, negative tumor-marker status, and avascularity in the lesion help to differentiate testicular epidermoid cyst from other germ cell tumors (111). Care of these patients is based on results of total urologic evaluation followed by excisional biopsy findings that provide the final diagnosis and suggest the treatment.
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Figure 14. Surgically proved intratesticular epidermoid cyst in a 21-year-old man. Longitudinal US scan of left testis reveals a well-circumscribed hypoechoic mass with a concentric lamellar pattern (curved arrow) of alternating hyper- and hypoechoic rings. This US appearance is referred to as the onion-ring appearance and is characteristic of epidermoid cyst. (Reprinted, with permission, from reference 115.)
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Tubular ectasia of rete testis.—Tubular ectasia of the rete testis is a benign condition resulting from partial or complete obliteration of the efferent ducts that cause ectasia of the rete testis. The US appearance is of fluid-filled tubular structures (Fig 15). Tubular ectasia occurs in men older than 55 years and is frequently bilateral. Findings of cystic dilatation in or adjacent to the mediastinum testis and the presence of epididymal cysts are characteristics of tubular ectasia and aid in distinguishing it from malignant cystic testicular tumors, which can occur anywhere in the testicular parenchyma (13).
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Figure 15. Tubular ectasia in a 60-year-old man. Longitudinal US scan of the testis reveals multiple channels (arrow) on the posterolateral aspect of the testis. Color Doppler US (not shown) did not demonstrate any flow.
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Intratesticular spermatocele.—An intratesticular spermatocele is a cystic intraparenchymal lesion attached to the mediastinum in the area of the rete testis. It communicates with the seminiferous tubules, unlike simple ectasia of the rete testis, which does not communicate directly with the seminiferous tubule (112,113). These cysts contain spermatozoa and can be septated.
Intratesticular varicocele.—The pathogenesis and clinical implications of the newly defined condition intratesticular varicocele are not yet well established. An intratesticular varicocele can occur in association with an extratesticular varicocele, but intratesticular varicoceles are more commonly found alone (114). Patients with intratesticular varicocele may have pain related to passive congestion of the testis, which eventually stretches the tunica albuginea. The US appearance of an intratesticular varicocele is similar to that of an extratesticular varicocele. US features include multiple anechoic, serpiginous, tubular structures of varying sizes. Color flow and duplex Doppler US demonstrate the venous flow pattern with a characteristic venous spectral waveform that increases during a Valsalva maneuver (Fig 16) (43).
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Figure 16a. Intratesticular varicocele in a 38-year-old man. (a) Transverse oblique US scan of left testis reveals multiple intratesticular anechoic cystic areas (arrowhead). (b) Duplex Doppler US scan shows that venous flow in these cystic areas increases during a Valsalva maneuver (arrowhead).
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Figure 16b. Intratesticular varicocele in a 38-year-old man. (a) Transverse oblique US scan of left testis reveals multiple intratesticular anechoic cystic areas (arrowhead). (b) Duplex Doppler US scan shows that venous flow in these cystic areas increases during a Valsalva maneuve | |
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INGUINAL AND SCROTAL SWELLING...
CONDITIONS OF THE SPERMATIC...
