(Radiology. 2000;217:219-227.)
© RSNA, 2000
Scrotal Disorders: Evaluation of Testicular Enhancement Patterns at Dynamic Contrast-enhanced Subtraction MR Imaging1
Yuji Watanabe, MD,
Masako Dohke, MD,
Kazutoshi Ohkubo, MD,
Takayoshi Ishimori, MD,
Yoshiki Amoh, MD,
Akira Okumura, MD,
Kazushige Oda, MD,
Takafumi Hayashi, MD,
Yoshihiro Dodo, MD and
Yoichi Arai, MD
1 From the Depts of Radiology (Y.W., M.D., T.I., Y.Amoh, A.O., K. Oda, T.H., Y.D.) and Urology (K. Ohkubo, Y.Arai), Kurashiki Central Hospital, 1-1-1 Miwa, Kurashiki, 710-8602, Japan. From the 1997 RSNA scientific assembly. Received Sep 2, 1999; revision requested Oct 8; revision received Dec 8; accepted January 12, 2000. Address correspondence to Y.W. (e-mail: yw5904@kchnet.or.jp).
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ABSTRACT
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PURPOSE: To evaluate testicular enhancement patterns in various scrotal disorders at dynamic contrast medium–enhanced subtraction magnetic resonance (MR) imaging.
MATERIALS AND METHODS: Forty-two patients with scrotal symptoms (22 testicular diseases, 20 extratesticular scrotal disorders) underwent three-dimensional (3D) fast field-echo or fast spin-echo dynamic subtraction MR imaging after injection of paramagnetic contrast medium. The relative percentages of peak height and mean slope of the testes on the affected side were compared with those on the unaffected side by using time–signal intensity curves.
RESULTS: Extratesticular scrotal disorders (time–signal intensity curve mean peak height, 93.1%; mean slope, 89.8%) showed gradual and progressive increase in homogeneous testicular contrast enhancement in all normal testes. Relative percentages of peak height and mean slope of testicular torsion (mean peak height, 17.3%; mean slope, 10.6%), infarction (mean peak height, 30.4%; mean slope, 19.8%), traumatic hemorrhagic necrosis (mean peak height, -3.5%; mean slope, -12.0%), and epidermoid cyst (mean peak height, -6.6%; mean slope, -14.2%) were significantly lower than those of extratesticular scrotal disorders. Acute mumps orchitis (mean peak height, 135.1%; mean slope, 307.5%) and malignant testicular tumor (mean peak height, 178.7%; mean slope, 467.6%) showed higher relative percentages of peak height and mean slope.
CONCLUSION: Dynamic contrast-enhanced subtraction MR imaging can provide information about testicular perfusion on the basis of contrast enhancement and can be used to differentiate testicular diseases from scrotal disorders.
Index terms: Epididymitis, 847.214 • Magnetic resonance (MR), contrast enhancement, 847.121411, 847.121415, 847.121416 • Magnetic resonance (MR), rapid imaging, 847.121416 • Magnetic resonance (MR), three-dimensional, 847.121411, 847.121415, 847.121416 • Scrotum, diseases, 847.1437, 847.214, 847.311, 969.756 • Scrotum, MR, 847.121411, 847.121415, 847.121416 • Testis, abnormalities, 847.1437, 847.1477, 847.219, 847.311, 847.91 • Testis, neoplasms, 847.30 • Testis, torsion, 847.1437 • Testis, undescended, 847.1477 • Varicocele, 969.756
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INTRODUCTION
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Scrotal diseases can be divided into testicular diseases and extratesticular scrotal disorders. In patients with scrotal symptoms such as pain, swelling, and redness, it is important to differentiate testicular diseases from extratesticular scrotal disorders (1,2). Testicular diseases, including testicular torsion, malignant testicular tumor, and traumatic damage, require surgical exploration, whereas other testicular diseases and extratesticular scrotal disorders such as acute epididymo-orchitis, appendiceal torsion, and so on can be treated by means of conservative therapy (1–3).
Misdiagnosis of testicular torsion and delay in performing surgery can lead to irreversible damage to the testis, which may cause not only potential fertility problems for the patient but also medicolegal problems for the clinician (2–4). If traumatic testicular hemorrhagic necrosis is left untreated, serious complications, including ischemic atrophy or infection, may occur. In such clinical settings, accurate evaluation of scrotal disease requires information about not only morphology but also testicular perfusion. Therefore, it is necessary to evaluate testicular blood flow and document whether it is normal, impaired, or increased to decide whether to treat a patient with scrotal symptoms surgically or conservatively.
A variety of imaging modalities, such as gray-scale ultrasonography (US), color or power Doppler US, and radionuclide scintigraphy, have been used to diagnose scrotal disease with high sensitivity and specificity, but they are not always accurate (5–12). Use of color and power Doppler US has become a well-accepted method for the evaluation of testicular blood flow (5–8). However, detectability of blood flow depends on patient age, testicular volume, sensitivity of the US equipment used, and operator skill. In addition, in the prepubertal age group, detection of testicular blood flow is inconsistent and shows great variability (7,9). Therefore, inconclusive color and power Doppler US results require use of another imaging modality for assessment of testicular blood flow (10–12).
Magnetic resonance (MR) imaging with use of a dynamic contrast medium–enhanced subtraction technique can provide information about testicular perfusion because of its high sensitivity for the enhancement induced by paramagnetic contrast media (13–16). The purpose of this study was to evaluate the different enhancement patterns of the testes in testicular and extratesticular diseases at dynamic contrast medium–enhanced subtraction MR imaging.
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MATERIALS AND METHODS
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Forty-two patients (age range, 4–80 years; mean age, 33 years) were enrolled consecutively in this study, which was approved by the institutional review board of our hospital. All patients presented with scrotal pain, swelling, or both. Written informed consent was obtained before the examination. The final diagnoses were 22 testicular diseases—testicular torsion (n = 7), testicular infarction (n = 3), traumatic testicular hemorrhagic necrosis (n = 2), malignant testicular tumor (n = 4), testicular epidermoid cyst (n = 2), acute mumps orchitis (n = 2), and undescended testis (n = 7)—and 20 extratesticular scrotal disorders—acute epididymitis (n = 6), appendiceal torsion (n = 6), epididymal cyst (n = 6), varicocele (n = 1), and scrotal skin metastasis (n = 1).
All the testicular torsions, testicular infarctions, traumatic testicular hemorrhagic necroses, malignant testicular tumors, testicular epidermoid cysts, appendiceal torsions, and the varicocele were confirmed by means of histologic examination after surgical exploration. Both patients with acute mumps orchitis had elevated serum antibody levels against mumps virus. All the undescended testes were confirmed by means of surgical exploration before orchiopexy. Of the six cases of acute epididymitis, one was confirmed by means of surgical exploration, and five were confirmed by means of clinical follow-up until symptoms and physical findings completely resolved by means of antibiotic therapy. Of the six cases of epididymal cysts, two were confirmed by means of surgical excision, and the other four were confirmed by means of follow-up US. The single scrotal skin metastasis was confirmed by means of histologic examination after biopsy of the scrotal skin.
MR Imaging
MR imaging was performed with a 1.5-T superconducting magnet system (Gyroscan ACS-NT; Philips Medical Systems, Best, the Netherlands) with 15 mT/m gradient. Each patient was positioned supine on the patient table, with the penis fixed on the lower abdominal wall. A commercially available 25-cm circular surface coil was placed on the patient’s lower pelvis and centered over the scrotum. The bilateral testes were arranged to maintain the same distance from the surface coil. After initial T1-weighted localizing images were obtained in the sagittal, coronal, and transverse directions, T1-weighted (450/15 [repetition time msec/echo time msec]), fat-saturated T2-weighted fast spin-echo (1,800/100), and T2*-weighted fast field-echo (600/30; flip angle, 20°) images were obtained. All images were obtained in the coronal direction with a 256 x 256 matrix, 4-mm section thickness, 0.4-mm section gap, 220-mm field of view, and two signals acquired. In some cases, additional transverse images were obtained by using the same parameters as those used for the coronal images.
After this examination, which routinely was performed in less than 25 minutes, dynamic contrast-enhanced subtraction MR imaging was performed with a three-dimensional (3D) fast field-echo sequence or fat-saturated fast spin-echo sequence. Peripheral intravenous tubing with a 19-gauge needle was placed into a subcutaneous vein of the forearm or antecubital fossa. The dynamic contrast-enhanced subtraction MR imaging was performed in the coronal plane.
A 3D fast field-echo sequence (10.2/4.1; flip angle, 35°) and fat-saturated fast spin-echo sequence (514/16; echo train length, three) were used in the first 33 (age range, 4–80 years; mean age, 30 years) and the next nine (age range, 12–68 years; mean age, 43 years) consecutive patients, respectively. Other imaging parameters of the 3D fast field-echo sequence were as follows: two signals acquired, 72-mm slab thickness, 4-mm section thickness (2-mm overlapping sections), partial-echo acquisition in the frequency-encoding direction, 220-mm field of view, 205 x 256 matrix, and 61 seconds per sequence. Other imaging parameters of the fat-saturated fast spin-echo sequence were as follows: two signals acquired, low-to-high k-space trajectory, 5-mm section thickness, 0.5-mm section gap, six sections acquired, 250-mm field of view, 205 x 256 matrix, and 60 seconds per sequence.
Images were obtained before and after rapid intravenous injection of a bolus of 0.1 mmol of gadopentetate dimeglumine (Magnevist; Nihon Schering, Osaka, Japan) per kilogram of body weight. The rapid injection of gadopentetate dimeglumine was performed within 5 seconds, followed by a flush of 20 mL of physiologic saline solution. Five imaging sets were obtained consecutively immediately after the injection of gadopentetate dimeglumine. The first four imaging sets were obtained with no interval between sets, but the last imaging set was obtained 1.5 minutes after the end of the fourth imaging set. During the actual examination time of approximately 8 minutes, the patients breathed normally, and no special instructions were given.
The data set obtained immediately before administration of gadopentetate dimeglumine was used as a mask for subsequent image subtraction. The subtraction was performed by using commercially available software (Philips Medical Systems). Each of the five original data sets obtained after administration of gadopentetate dimeglumine was subtracted section by section.
Image and Statistical Analysis
For the dynamic contrast-enhanced subtraction MR images, time–signal intensity curves were created from circular or round operator-defined regions of interest drawn over the testes by three radiologists (Y.W., M.D., T.I.) by means of consensus. The region of interest was as large as possible to minimize noise, and care was taken to avoid partial-volume effect and subtraction artifact. The diameter of the region of interest accordingly was about 70%–80% of the diameter of the testes. When the testes with testicular tumor, testicular epidermoid cyst, and traumatic testicular hemorrhagic necrosis showed inhomogeneous enhancement, the region of interest was placed on only the lesion, and the diameter of the region of interest was about 70%–80% of the diameter of the lesion.
If there was substantial subtraction artifact from motion or adjacent arterial pulsation, the image was eliminated from data analysis. The time points for the data sets were defined according to the k-space trajectory as 30, 90, 150, 210, or 360 seconds after injection of gadopentetate dimeglumine for the 3D fast field-echo sequence and as 15, 75, 135, 195, or 345 seconds after injection of gadopentetate dimeglumine for the fast spin-echo sequence.
The data were transferred to a personal computer (Power Macintosh 9500/200; Apple Computer, Tokyo, Japan), and gamma variate fits were performed on the time–signal intensity curves with commercially available software (DeltaGraph version 4.0; Delta Point, Tokyo, Japan). Excellent curve fits for time–signal intensity curves were attained. Among the 42 patients, only one image of a patient with acute epididymitis was eliminated from data analysis because of motion artifacts.
Peak height, defined as the maximum value of the time–signal intensity curve, was determined for the testes on both the affected and unaffected sides, and the relative percentage of peak height of the testes on the affected side was calculated by using the following formula: relative percentage of peak height = (peak height of the affected testis x 100)/peak height of the unaffected testis. The mean slope of the testicular enhancement during the first 4 minutes after injection of gadopentetate dimeglumine was determined after fitting the measured data according to the linear function. The relative percentage of mean slope of the testes on the affected side was calculated by using the following formula: relative percentage of mean slope = (mean slope of the affected testis x 100)/mean slope of the unaffected testis.
All values were expressed as a mean plus or minus SD. The significance of the differences between groups was analyzed by means of an unpaired Student t test. A P value less than .05 was considered statistically significant.
The enhancement pattern was evaluated on the image that was maximally enhanced and was classified as follows: homogeneous, if enhancement of the testis on the affected side was completely homogeneous; heterogeneous, if enhancement of the testis on the affected side was completely heterogeneous; partial absence, if the testis on the affected side showed a focal lesion of no enhancement; no enhancement, if enhancement of the testis on the affected side was totally absent. If a testis tended to go from heterogeneous to homogeneous enhancement with time, the enhancement pattern was determined on the image obtained at the peak of enhancement. The enhancement pattern of the testes on the affected side was determined by three radiologists (Y.W., M.D., T.I.) together by means of consensus. When a discrepancy occurred, consensus was reached by means of discussion. No laboratory data or other imaging results were available for image interpretation in any of the patients.
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RESULTS
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The time–signal intensity curves of all the normal testes were similar between the fat-saturated fast spin-echo and 3D fast field-echo sequences. The curves also showed a gradual and progressive increase to the peak height, at which they maintained a plateau, although a much larger increase in signal intensity of the normal testes was seen in the fat-saturated fast spin-echo sequence than in the 3D fast field-echo sequence (Fig 1). Enhancement of the testes on the affected side for the two sequences showed no significant difference when the data were compared and normalized with those for the testes on the unaffected side.
The time–signal intensity curves of the testes on the affected side appeared different for the various scrotal disorders; the characteristics of the time–signal intensity curves are summarized in the Table and Figure 2. The time–signal intensity curve of testicular torsion, testicular infarction, and traumatic testicular hemorrhagic necrosis usually showed little or no increase after injection of contrast medium. Conversely, malignant testicular tumors and acute mumps orchitis showed a rapid increase in enhancement after injection of contrast medium; after the testes reached maximum enhancement, the time–signal intensity curve declined slightly or maintained a plateau. The time–signal intensity curve of the testicular epidermoid cyst showed no increase after injection of contrast medium. The undescended testes and extratesticular scrotal disorders, including acute epididymitis, appendiceal torsion, epididymal cyst, varicocele, and scrotal skin metastasis, showed time–signal intensity curves similar to those of the normal testes.
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Figure 2a. Mean values plus or minus 1 SD of the (a) relative percentage of peak height and (b) relative percentage of mean slope for each testicular disease and extratesticular scrotal disorders. Extratesticular scrotal disorders have little effect on testicular enhancement and show around 100% of both the mean relative percentages of peak height (93.1%) and slope (89.9%). Testicular torsion, infarction, trauma, and epidermoid cyst show significantly low values for both the relative percentage of peak height and relative percentage of mean slope when compared with those for extratesticular scrotal disorders. Malignant testicular tumor and acute mumps orchitis show significantly high values for both the relative percentage of peak height and relative percentage of mean slope.
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Figure 2b. Mean values plus or minus 1 SD of the (a) relative percentage of peak height and (b) relative percentage of mean slope for each testicular disease and extratesticular scrotal disorders. Extratesticular scrotal disorders have little effect on testicular enhancement and show around 100% of both the mean relative percentages of peak height (93.1%) and slope (89.9%). Testicular torsion, infarction, trauma, and epidermoid cyst show significantly low values for both the relative percentage of peak height and relative percentage of mean slope when compared with those for extratesticular scrotal disorders. Malignant testicular tumor and acute mumps orchitis show significantly high values for both the relative percentage of peak height and relative percentage of mean slope.
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The mean relative percentage of peak height of the extratesticular scrotal disorders was 93.1% ± 11.6 (SD), which reflects similar contrast enhancement between the testes on the affected side and those on the unaffected side. Testicular torsion, testicular infarction, traumatic testicular hemorrhagic necrosis, and testicular epidermoid cyst showed significantly lower relative percentages of peak height than did the extratesticular scrotal disorders (P < .001) (Table, Fig 2). In contrast, malignant testicular tumors and acute mumps orchitis showed significantly higher relative percentages of peak height than did the extratesticular scrotal disorders (P < .001) and each of the testicular diseases showing decreased relative percentage of peak height (P < .01) (Table, Fig 2). No significant differences in the relative percentages of peak height were found between the undescended testes and the extratesticular scrotal disorders.
The relative percentage of mean slope for early contrast enhancement showed a similar tendency as that seen for the relative percentage of peak height (Table, Fig 2). The relative percentage of mean slope of the extratesticular scrotal disorders was 89.9% ± 15.2, which reflects similar contrast enhancement between the testes on the affected side and those on the unaffected side. Testicular torsion, testicular infarction, traumatic testicular hemorrhagic necrosis, and testicular epidermoid cyst showed a significantly lower relative percentage of mean slope than did the extratesticular scrotal disorders (P < .001). In contrast, malignant testicular tumors and acute mumps orchitis showed a significantly higher relative percentage of mean slope than did the extratesticular scrotal disorders (P < .001), which showed marked increase in comparison with the relative percentage of peak height. No significant differences in the relative percentage of mean slope were found between the undescended testes and the extratesticular scrotal disorders.
The contrast enhancement patterns of the normal testes were constantly homogeneous (Figs 3–9). Among the seven cases of testicular torsion, six twisted testes showed no enhancement (Fig 3), and only one twisted testis showed a little enhancement with a homogeneous pattern. The two cases of traumatic testicular hemorrhagic necrosis (Fig 4), the three cases of testicular infarction (Fig 5), and the four cases of malignant testicular tumors (Fig 6) showed a heterogeneous pattern; all cases of traumatic testicular hemorrhagic necrosis and infarction showed mixed enhancement, including areas ranging from normal to no enhancement, whereas all the malignant tumors showed mixed enhancement, including areas ranging from marked increase to no enhancement (Figs 4–6).
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Figure 3a. Surgically proved testicular torsion with hemorrhagic necrosis in a 15-year-old adolescent boy. The MR imaging examination was performed 48 hours after the onset of left scrotal pain. (a) Coronal fat-saturated T2-weighted fast spin-echo MR image (1,800/100) of the left testis (arrow) shows slightly low signal intensity. Note that the left epididymis (arrowhead) shows low signal intensity. On the coronal dynamic contrast-enhanced subtraction 3D fast field-echo MR images (10.2/4.1; flip angle, 35°) obtained (b) 90 and (c) 360 seconds after injection of contrast medium, the left testis (solid arrows) shows no contrast enhancement, while the right testis shows gradual and progressive increase in homogeneous contrast enhancement. Note that the left epididymis (arrowhead) is not enhanced at all, and the tunica vaginalis (open arrow) is well enhanced. The relative percentages of peak height and mean slope are 8.0% and 11.6%, respectively.
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Figure 3b. Surgically proved testicular torsion with hemorrhagic necrosis in a 15-year-old adolescent boy. The MR imaging examination was performed 48 hours after the onset of left scrotal pain. (a) Coronal fat-saturated T2-weighted fast spin-echo MR image (1,800/100) of the left testis (arrow) shows slightly low signal intensity. Note that the left epididymis (arrowhead) shows low signal intensity. On the coronal dynamic contrast-enhanced subtraction 3D fast field-echo MR images (10.2/4.1; flip angle, 35°) obtained (b) 90 and (c) 360 seconds after injection of contrast medium, the left testis (solid arrows) shows no contrast enhancement, while the right testis shows gradual and progressive increase in homogeneous contrast enhancement. Note that the left epididymis (arrowhead) is not enhanced at all, and the tunica vaginalis (open arrow) is well enhanced. The relative percentages of peak height and mean slope are 8.0% and 11.6%, respectively.
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Figure 3c. Surgically proved testicular torsion with hemorrhagic necrosis in a 15-year-old adolescent boy. The MR imaging examination was performed 48 hours after the onset of left scrotal pain. (a) Coronal fat-saturated T2-weighted fast spin-echo MR image (1,800/100) of the left testis (arrow) shows slightly low signal intensity. Note that the left epididymis (arrowhead) shows low signal intensity. On the coronal dynamic contrast-enhanced subtraction 3D fast field-echo MR images (10.2/4.1; flip angle, 35°) obtained (b) 90 and (c) 360 seconds after injection of contrast medium, the left testis (solid arrows) shows no contrast enhancement, while the right testis shows gradual and progressive increase in homogeneous contrast enhancement. Note that the left epididymis (arrowhead) is not enhanced at all, and the tunica vaginalis (open arrow) is well enhanced. The relative percentages of peak height and mean slope are 8.0% and 11.6%, respectively.
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Figure 4a. Surgically proved traumatic testicular hemorrhagic necrosis in a 22-year-old man. The MR imaging examination was performed 48 hours after an episode of blunt traumatic scrotal damage. (a) Coronal fat-saturated T2-weighted fast spin-echo MR image (1,800/100) of the right testis (arrow) shows inhomogeneously low signal intensity. On the coronal dynamic contrast-enhanced subtraction fast spin-echo MR images (514/16) obtained (b) 15 and (c) 345 seconds after injection of contrast medium, the right testis (arrow) shows heterogeneous contrast enhancement consisting of a small central part of minimal enhancement and a large part of no enhancement, while the left testis shows gradual and progressive increase in homogeneous contrast enhancement. The relative percentages of peak height and mean slope are -5.0% and -8.1%, respectively.
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Figure 4b. Surgically proved traumatic testicular hemorrhagic necrosis in a 22-year-old man. The MR imaging examination was performed 48 hours after an episode of blunt traumatic scrotal damage. (a) Coronal fat-saturated T2-weighted fast spin-echo MR image (1,800/100) of the right testis (arrow) shows inhomogeneously low signal intensity. On the coronal dynamic contrast-enhanced subtraction fast spin-echo MR images (514/16) obtained (b) 15 and (c) 345 seconds after injection of contrast medium, the right testis (arrow) shows heterogeneous contrast enhancement consisting of a small central part of minimal enhancement and a large part of no enhancement, while the left testis shows gradual and progressive increase in homogeneous contrast enhancement. The relative percentages of peak height and mean slope are -5.0% and -8.1%, respectively.
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Figure 4c. Surgically proved traumatic testicular hemorrhagic necrosis in a 22-year-old man. The MR imaging examination was performed 48 hours after an episode of blunt traumatic scrotal damage. (a) Coronal fat-saturated T2-weighted fast spin-echo MR image (1,800/100) of the right testis (arrow) shows inhomogeneously low signal intensity. On the coronal dynamic contrast-enhanced subtraction fast spin-echo MR images (514/16) obtained (b) 15 and (c) 345 seconds after injection of contrast medium, the right testis (arrow) shows heterogeneous contrast enhancement consisting of a small central part of minimal enhancement and a large part of no enhancement, while the left testis shows gradual and progressive increase in homogeneous contrast enhancement. The relative percentages of peak height and mean slope are -5.0% and -8.1%, respectively.
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Figure 5a. Surgically proved testicular infarction in a 42-year-old man. The MR imaging examination was performed 72 hours after the onset of right scrotal pain. (a) Coronal fat-saturated T2-weighted fast spin-echo MR image (1,800/100) of an upper part of the right testis (arrow) shows low signal intensity. On the coronal dynamic contrast-enhanced subtraction fast spin-echo MR images (514/16) obtained (b) 75 and (c) 345 seconds after injection of contrast medium, the right testis shows heterogeneous contrast enhancement consisting of an upper part (solid arrow) of decreased enhancement and a lower part (open arrow) of normal enhancement, while the left testis shows gradual and progressive increase in homogeneous contrast enhancement. The relative percentages of peak height and mean slope are 47.9% and 24.4%, respectively.
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Figure 5b. Surgically proved testicular infarction in a 42-year-old man. The MR imaging examination was performed 72 hours after the onset of right scrotal pain. (a) Coronal fat-saturated T2-weighted fast spin-echo MR image (1,800/100) of an upper part of the right testis (arrow) shows low signal intensity. On the coronal dynamic contrast-enhanced subtraction fast spin-echo MR images (514/16) obtained (b) 75 and (c) 345 seconds after injection of contrast medium, the right testis shows heterogeneous contrast enhancement consisting of an upper part (solid arrow) of decreased enhancement and a lower part (open arrow) of normal enhancement, while the left testis shows gradual and progressive increase in homogeneous contrast enhancement. The relative percentages of peak height and mean slope are 47.9% and 24.4%, respectively.
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Figure 5c. Surgically proved testicular infarction in a 42-year-old man. The MR imaging examination was performed 72 hours after the onset of right scrotal pain. (a) Coronal fat-saturated T2-weighted fast spin-echo MR image (1,800/100) of an upper part of the right testis (arrow) shows low signal intensity. On the coronal dynamic contrast-enhanced subtraction fast spin-echo MR images (514/16) obtained (b) 75 and (c) 345 seconds after injection of contrast medium, the right testis shows heterogeneous contrast enhancement consisting of an upper part (solid arrow) of decreased enhancement and a lower part (open arrow) of normal enhancement, while the left testis shows gradual and progressive increase in homogeneous contrast enhancement. The relative percentages of peak height and mean slope are 47.9% and 24.4%, respectively.
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Figure 6a. Surgically proved malignant testicular tumor of a mixed type of embryonal carcinoma and seminoma in a 42-year-old man. The MR imaging examination was performed 7 days after the onset of left scrotal pain and swelling. (a) Coronal fat-saturated T2-weighted fast spin-echo MR image (1,800/100) of the left testis (arrow) shows inhomogeneous signal intensity. On the coronal dynamic contrast-enhanced subtraction 3D fast field-echo MR images (10.2/4.1; flip angle, 35°) obtained (b) 30 and (c) 360 seconds after injection of contrast medium, the left testis (solid arrow) shows early and intense increase in heterogeneous contrast enhancement and a small central part (solid arrowhead in c) of no enhancement, while the right testis (open arrow) shows gradual and progressive increase in homogeneous contrast enhancement. Note that the left epididymis (open arrowhead) shows early and intense enhancement. The relative percentages of peak height and mean slope are 222.7% and 333.7%, respectively.
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Figure 6b. Surgically proved malignant testicular tumor of a mixed type of embryonal carcinoma and seminoma in a 42-year-old man. The MR imaging examination was performed 7 days after the onset of left scrotal pain and swelling. (a) Coronal fat-saturated T2-weighted fast spin-echo MR image (1,800/100) of the left testis (arrow) shows inhomogeneous signal intensity. On the coronal dynamic contrast-enhanced subtraction 3D fast field-echo MR images (10.2/4.1; flip angle, 35°) obtained (b) 30 and (c) 360 seconds after injection of contrast medium, the left testis (solid arrow) shows early and intense increase in heterogeneous contrast enhancement and a small central part (solid arrowhead in c) of no enhancement, while the right testis (open arrow) shows gradual and progressive increase in homogeneous contrast enhancement. Note that the left epididymis (open arrowhead) shows early and intense enhancement. The relative percentages of peak height and mean slope are 222.7% and 333.7%, respectively.
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Figure 6c. Surgically proved malignant testicular tumor of a mixed type of embryonal carcinoma and seminoma in a 42-year-old man. The MR imaging examination was performed 7 days after the onset of left scrotal pain and swelling. (a) Coronal fat-saturated T2-weighted fast spin-echo MR image (1,800/100) of the left testis (arrow) shows inhomogeneous signal intensity. On the coronal dynamic contrast-enhanced subtraction 3D fast field-echo MR images (10.2/4.1; flip angle, 35°) obtained (b) 30 and (c) 360 seconds after injection of contrast medium, the left testis (solid arrow) shows early and intense increase in heterogeneous contrast enhancement and a small central part (solid arrowhead in c) of no enhancement, while the right testis (open arrow) shows gradual and progressive increase in homogeneous contrast enhancement. Note that the left epididymis (open arrowhead) shows early and intense enhancement. The relative percentages of peak height and mean slope are 222.7% and 333.7%, respectively.
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Figure 7a. Surgically proved testicular epidermoid cyst in a 23-year-old man. The MR imaging examination was performed 3 months after the onset of left scrotal swelling. (a) Coronal fat-saturated T2-weighted fast spin-echo MR image (1,800/100) of the upper part of the left testis (arrow) shows a round area of high signal intensity. On the coronal dynamic contrast-enhanced subtraction 3D fast field-echo MR images (10.2/4.1; flip angle, 35°) obtained (b) 90 and (c) 360 seconds after injection of contrast medium, the left testis shows a round-shaped partial absence (arrow) of contrast enhancement surrounded by an area of normal enhancement, while the right testis shows gradual and progressive increase in homogeneous contrast enhancement. The relative percentages of peak height and mean slope of the round lesion are -26.6% and -32.7%, respectively.
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Figure 7b. Surgically proved testicular epidermoid cyst in a 23-year-old man. The MR imaging examination was performed 3 months after the onset of left scrotal swelling. (a) Coronal fat-saturated T2-weighted fast spin-echo MR image (1,800/100) of the upper part of the left testis (arrow) shows a round area of high signal intensity. On the coronal dynamic contrast-enhanced subtraction 3D fast field-echo MR images (10.2/4.1; flip angle, 35°) obtained (b) 90 and (c) 360 seconds after injection of contrast medium, the left testis shows a round-shaped partial absence (arrow) of contrast enhancement surrounded by an area of normal enhancement, while the right testis shows gradual and progressive increase in homogeneous contrast enhancement. The relative percentages of peak height and mean slope of the round lesion are -26.6% and -32.7%, respectively.
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Figure 7c. Surgically proved testicular epidermoid cyst in a 23-year-old man. The MR imaging examination was performed 3 months after the onset of left scrotal swelling. (a) Coronal fat-saturated T2-weighted fast spin-echo MR image (1,800/100) of the upper part of the left testis (arrow) shows a round area of high signal intensity. On the coronal dynamic contrast-enhanced subtraction 3D fast field-echo MR images (10.2/4.1; flip angle, 35°) obtained (b) 90 and (c) 360 seconds after injection of contrast medium, the left testis shows a round-shaped partial absence (arrow) of contrast enhancement surrounded by an area of normal enhancement, while the right testis shows gradual and progressive increase in homogeneous contrast enhancement. The relative percentages of peak height and mean slope of the round lesion are -26.6% and -32.7%, respectively.
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Figure 8a. Clinically proved acute mumps epididymo-orchitis in a 41-year-old man. The MR imaging examination was performed 5 days after the onset of left scrotal pain and swelling. (a) Coronal fat-saturated T2-weighted fast spin-echo MR image (1,800/100) of the left testis (arrow) shows lower signal intensity relative to that of the right testis. On the coronal dynamic contrast-enhanced subtraction 3D fast field-echo MR images (10.2/4.1; flip angle, 35°) obtained (b) 30 and (c) 360 seconds after injection of contrast medium, the left testis (arrow) shows early and strong increase in homogeneous contrast enhancement relative to the right testis, while the right testis shows gradual and progressive increase in contrast enhancement. Note that the left epididymis (arrowheads) shows early and intense enhancement. The relative percentages of peak height and mean slope are 134.4% and 311.3%, respectively.
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Figure 8b. Clinically proved acute mumps epididymo-orchitis in a 41-year-old man. The MR imaging examination was performed 5 days after the onset of left scrotal pain and swelling. (a) Coronal fat-saturated T2-weighted fast spin-echo MR image (1,800/100) of the left testis (arrow) shows lower signal intensity relative to that of the right testis. On the coronal dynamic contrast-enhanced subtraction 3D fast field-echo MR images (10.2/4.1; flip angle, 35°) obtained (b) 30 and (c) 360 seconds after injection of contrast medium, the left testis (arrow) shows early and strong increase in homogeneous contrast enhancement relative to the right testis, while the right testis shows gradual and progressive increase in contrast enhancement. Note that the left epididymis (arrowheads) shows early and intense enhancement. The relative percentages of peak height and mean slope are 134.4% and 311.3%, respectively.
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Figure 8c. Clinically proved acute mumps epididymo-orchitis in a 41-year-old man. The MR imaging examination was performed 5 days after the onset of left scrotal pain and swelling. (a) Coronal fat-saturated T2-weighted fast spin-echo MR image (1,800/100) of the left testis (arrow) shows lower signal intensity relative to that of the right testis. On the coronal dynamic contrast-enhanced subtraction 3D fast field-echo MR images (10.2/4.1; flip angle, 35°) obtained (b) 30 and (c) 360 seconds after injection of contrast medium, the left testis (arrow) shows early and strong increase in homogeneous contrast enhancement relative to the right testis, while the right testis shows gradual and progressive increase in contrast enhancement. Note that the left epididymis (arrowheads) shows early and intense enhancement. The relative percentages of peak height and mean slope are 134.4% and 311.3%, respectively.
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Figure 9a. Clinically proved acute epididymitis in a 16-year-old adolescent boy. The MR imaging examination was performed 6 days after the onset of right scrotal pain. (a) Coronal fat-saturated T2-weighted fast spin-echo MR image (1,800/100) of the right testis (arrow) shows homogeneous and similar signal intensity to that of the left testis. Note the enlarged right epididymis (arrowhead). On the coronal dynamic contrast-enhanced subtraction 3D fast field-echo MR images (10.2/4.1; flip angle, 35°) obtained (b) 30 and (c) 360 seconds after injection of contrast medium, the right testis (arrow) shows gradual and progressive increase in homogeneous contrast enhancement similar to that of the left testis. Note that the right epididymis (arrowhead) shows early and intense enhancement. The relative percentages of peak height and mean slope are 99.0% and 91.7%, respectively. Acute epididymitis subsequently was proved to have been caused by sexually transmitted infection with Chlamydia trachomatis.
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Figure 9b. Clinically proved acute epididymitis in a 16-year-old adolescent boy. The MR imaging examination was performed 6 days after the onset of right scrotal pain. (a) Coronal fat-saturated T2-weighted fast spin-echo MR image (1,800/100) of the right testis (arrow) shows homogeneous and similar signal intensity to that of the left testis. Note the enlarged right epididymis (arrowhead). On the coronal dynamic contrast-enhanced subtraction 3D fast field-echo MR images (10.2/4.1; flip angle, 35°) obtained (b) 30 and (c) 360 seconds after injection of contrast medium, the right testis (arrow) shows gradual and progressive increase in homogeneous contrast enhancement similar to that of the left testis. Note that the right epididymis (arrowhead) shows early and intense enhancement. The relative percentages of peak height and mean slope are 99.0% and 91.7%, respectively. Acute epididymitis subsequently was proved to have been caused by sexually transmitted infection with Chlamydia trachomatis.
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Figure 9c. Clinically proved acute epididymitis in a 16-year-old adolescent boy. The MR imaging examination was performed 6 days after the onset of right scrotal pain. (a) Coronal fat-saturated T2-weighted fast spin-echo MR image (1,800/100) of the right testis (arrow) shows homogeneous and similar signal intensity to that of the left testis. Note the enlarged right epididymis (arrowhead). On the coronal dynamic contrast-enhanced subtraction 3D fast field-echo MR images (10.2/4.1; flip angle, 35°) obtained (b) 30 and (c) 360 seconds after injection of contrast medium, the right testis (arrow) shows gradual and progressive increase in homogeneous contrast enhancement similar to that of the left testis. Note that the right epididymis (arrowhead) shows early and intense enhancement. The relative percentages of peak height and mean slope are 99.0% and 91.7%, respectively. Acute epididymitis subsequently was proved to have been caused by sexually transmitted infection with Chlamydia trachomatis.
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Both cases of testicular epidermoid cyst showed a round-shaped partial-absence pattern (Fig 7). Both cases of acute mumps orchitis (Fig 8) showed increased enhancement with a homogeneous pattern. The undescended testes and all the extratesticular scrotal disorders, including acute epididymitis (Fig 9), appendiceal torsion, varicocele, and scrotal skin metastasis, showed a homogeneous pattern of contrast enhancement similar to that of the normal testes. Visual evaluation of the degree of contrast enhancement was in accordance with the relative percentages of peak height and mean slope.
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DISCUSSION
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It is important to evaluate whether testicular blood flow is normal, impaired, or increased in order to decide whether to manage scrotal symptoms surgically or conservatively. The process of imaging depends on the local expertise available. Although a combination of color Doppler US and radionuclide scintigraphy has been the mainstay for assessing testicular blood flow in patients suspected of having testicular torsion, it is not always accurate (10–12). Detectability of testicular blood flow by means of color or power Doppler US depends on patient age, testicular volume, and operator skill.
MR imaging has been thought to play a minor and questionable role in the evaluation scrotal symptoms (3,13). However, in this study, dynamic contrast-enhanced subtraction MR imaging was capable of depicting testicular blood flow on the basis of testicular contrast enhancement, even in a 4-year-old boy. With our methods, all the normal testes showed a gradual and progressive increase in contrast enhancement. Comparison of contrast enhancement between the right and left testes, in which the testis on the unaffected side serves as a normal control, facilitates the evaluation of contrast enhancement of the testis on the affected side. The subtraction technique allows for visual assessment of testicular contrast enhancement and is necessary for accurate assessment of contrast enhancement, especially in a normal prepubertal testis or in a testis that is T1 hyperintense due to hemorrhagic necrosis.
Contrast enhancement of the normal testes that was attained by using the fat-saturated fast spin-echo sequence was more conspicuous than that attained by using the 3D fast field-echo sequence, although the time–signal intensity curves of the normal testes seemed similar between the two pulse sequences. The major differences between the two sequences, during similar data acquisition times, were the imaging coverage of slab thickness, section thickness, and contrast enhancement of testes and vessels.
The 3D fast field-echo sequence has some advantages over the fat-saturated fast spin-echo sequence: thicker slabs with thinner sections and depiction of enhancement of not only the testis but also the femoral artery and vein. However, the intense enhancement of femoral vessels on 3D fast field-echo images has an unfavorable effect on the depiction of contrast enhancement of the testis itself—that is, the dynamic range of depiction of testicular enhancement is narrowed as shown in Figure 1. In contrast, fat-saturated fast spin-echo images show minimal enhancement of femoral vessels and provide a wide dynamic range of depiction of testicular enhancement. Therefore, the fat-saturated fast spin-echo sequence seems preferable to the 3D fast field-echo sequence in the evaluation of testicular enhancement patterns.
The increase in tissue signal intensity after contrast enhancement depends on the blood supply and the volume of the extravascular fluid in the tissue (17,18). Early changes in the time–signal intensity curve in a region of interest correlate with blood flow, and the later changes mainly correlate with interstitial extravascular accumulation of contrast medium through capillary permeability. The different appearances of the time–signal intensity curves among the testicular diseases represent the differences in both testicular blood flow and extravascular fluid space associated with the extracellular fluid volume and the diffusing spread of contrast medium. The peak height attained by using our methods may not be an exact peak height, however, because measurement of signal intensity was performed at 1-minute intervals.
In the study by Costabile et al (15), a T2*-weighted gradient-echo dynamic enhanced MR imaging sequence was used for detection of testicular perfusion. Images were obtained every 2 seconds for detection of early decrease in signal intensity after injection of a bolus of contrast medium. However, T2*-weighted images may not be sensitive for detection of late contrast enhancement and are vulnerable to susceptibility artifacts that result from the air-tissue interface, which may distort images and hamper accurate measurement of signal intensity. Our method can provide information about testicular perfusion, extracellular fluid volume, and tissue homogeneity through analyzing measurements from the time–signal intensity curve and contrast enhancement pattern.
Our results indicate that both the relative percentage of peak height and the relative percentage of mean slope, on the basis of the time–signal intensity curves, might be helpful not only in distinguishing testicular diseases from extratesticular diseases but also in dividing testicular diseases into two groups: one group of diseases with no or decreased contrast enhancement, including testicular torsion, testicular infarction, traumatic testicular hemorrhagic necrosis, and testicular epidermoid cyst, and the other group of diseases with increased contrast enhancement, including malignant testicular tumors and acute mumps orchitis. Undescended testes showed no significant difference in relative percentages of peak height or mean slope compared with those of the extratesticular scrotal disorders.
No contrast medium or a little is delivered in testes in which testicular blood flow is impaired and/or irreversible damage such as hemorrhagic necrosis has occurred. In such a clinical setting, prompt surgical exploration should be considered for the purpose of salvaging the damaged testes or preventing formation of antisperm and antitestical autoantibodies (2–4). Accordingly, decreased relative percentages of peak height and mean slope, seen in testicular torsion, infarction, and traumatic hemorrhagic necrosis, would be good indicators of the necessity for surgical exploration. Although the testicular epidermoid cyst, which is a benign tumor and may not always require surgery, also showed low relative percentages of peak height and mean slope, the contrast enhancement pattern seen in epidermoid cyst was different from those seen in testicular torsion, infarction, and traumatic hemorrhagic necrosis. The partial-absence pattern was observed exclusively in the testicular epidermoid cyst.
In contrast, increased contrast medium was delivered in hypervascular malignant testicular tumors and testicular inflammation. All cases of malignant testicular tumors and acute mumps orchitis showed a remarkably higher relative percentage of mean slope and a slightly higher relative percentage of peak height than did the extratesticular scrotal disorders. Our methods may not catch the exact peak time point, but high relative percentage of mean slope is thought to represent increased blood flow in the testis on the affected side. Furthermore, the contrast enhancement pattern can allow for differentiation of malignant testicular tumors from acute mumps orchitis. All the malignant tumors showed a heterogeneous pattern, whereas all cases of acute mumps orchitis showed a homogeneous pattern.
The combination of measurements obtained from time–signal intensity curves with contrast enhancement patterns can allow differentiation of testicular diseases that require surgical exploration from extratesticular scrotal disorders that do not. If we consider the homogeneous pattern of relative percentage of peak height of 70%–115% and relative percentage of mean slope of 50%–125% as the criteria for differentiating extratesticular diseases from testicular diseases, and if we also preclude undescended testis, there would be 20 of 20 extratesticular diseases diagnosed accurately and 20 of 20 testicular diseases diagnosed accurately. Sensitivity, specificity, and accuracy would be all 100%. In particular, testicular torsion requires emergency surgery and should be differentiated from other extratesticular scrotal disorders such as acute epididymitis and appendiceal torsion.
The results shown in our study may encourage application of our methods for differentiation of testicular torsion from acute epididymitis, and so on. In such a clinical setting as inconclusive color or power Doppler US results, our method would be useful in determining when and how to perform surgery. Even when Doppler US provides reliable results, MR imaging would play the role of a confirmation study and provide the confidence for urologists to decide how to manage acute scrotal symptoms.
Furthermore, the combination of findings obtained by means of nonenhanced and dynamic contrast-enhanced subtraction MR imaging can allow urologists to determine what surgery should be performed in a patient with testicular torsion—orchiectomy or orchiopexy. When a twisted testis shows hypoperfusion or lack of perfusion and simultaneously demonstrates abnormal signal intensity on fat-saturated T2-weighted images, the diagnosis would be testicular torsion with hemorrhagic necrosis, and then orchiectomy might be the surgery of choice. When a twisted testis demonstrates hypoperfusion or lack of perfusion and shows no abnormal signal intensity on fat-saturated T2-weighted images, the diagnosis would be testicular torsion without any irreversible damage, and therefore emergent surgical untwisting and orchiopexy could be used to salvage the affected testis. However, further investigation on a large scale is necessary to establish the specificity and sensitivity of this technique in evaluating scrotal disorders.
In conclusion, dynamic contrast-enhanced subtraction MR imaging can provide information about testicular perfusion by means of testicular contrast enhancement and can be used to diagnose scrotal disorders and differentiate testicular diseases from extratesticular scrotal disorders.
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ACKNOWLEDGMENTS
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We thank the secretaries, Hiroko Suyama, BS, and Naoko Hirakawa, BS, for preparing the manuscript and figures and also the radiology technologists of the MR division for technical support.
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FOOTNOTES
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See also the editorial by Choyke (pp 14–15
) in this issue.
Author contributions: Guarantors of integrity of entire study, Y.W., M.D., Y.D.; study concepts, Y.W., M.D., Y.Arai; study design, Y.W., M.D.; definition of intellectual content, Y.W., M.D., K.Ohkubo; literature research, Y.W., M.D., T.I., Y.Arai, Y.Amoh; clinical studies, T.H., A.O., Y.W., M.D., K.Oda, T.I.; data acquisition and analysis, Y.W., M.D., T.I.; statistical analysis, Y.W., M.D.; manuscript preparation, Y.W., M.D., Y.Arai; manuscript editing, Y.W.; manuscript review, Y.W., M.D.
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TOP
ABSTRACT
INTRODUCTION
) and fat-saturated fast spin-echo (514/16; n = 9; 
) sequences. The normal testes show a gradual and progressive increase and reach a plateau at about 200 seconds after injection of a bolus of contrast medium in both sequences, although the increase in signal intensity is much larger for the fat-saturated fast spin-echo sequence than for the 3D fast field-echo sequence. Error bars indicate SD.