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Lymphangioleiomyomatosis: Abdominopelvic CT and US Findings¹

¹ From the Diagnostic Radiology Department, Warren Grant Magnuson Clinical Center (N.A.A., A.J.D.), and the Pulmonary–Critical Care Medical Branch, National Heart, Lung, and Blood Institute (J.A.K., S.C.C., J.M.), National Institutes of Health, Bldg 10, Rm 1C-660, 10 Center Dr MSC 1182, Bethesda, MD 20892-1182. Received May 18, 1999; revision requested October 1; final revision received November 1; accepted November 10. Address correspondence to N.A.A. (e-mail: navila@nih.gov).

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
PURPOSE: To describe the abdominal computed tomographic (CT) and ultrasonographic (US) findings in patients with thoracic lymphangioleiomyomatosis (LAM) and to relate the prevalence of the findings to the severity of pulmonary disease.

MATERIALS AND METHODS: Eighty patients with LAM underwent chest and abdominopelvic CT and abdominopelvic US. The images were reviewed prospectively by one radiologist, and the abdominal findings were recorded and correlated with the severity of pulmonary disease at thin-section CT.

RESULTS: Sixty-one (76%) of 80 patients had positive abdominal findings. The most common abdominal findings included renal angiomyolipoma (AML) in 43 patients (54%), enlarged abdominal lymph nodes in 31 (39%), and lymphangiomyoma in 13 (16%). Less common findings included ascites in eight (10%), dilatation of the thoracic duct in seven (9%), and hepatic AML in three (4%). A significant correlation (P = .02) was observed between enlarged abdominal lymph nodes and increased severity of lung disease.

CONCLUSION: There are characteristic abdominal findings in patients with LAM that, in conjunction with the classic thin-section CT finding of pulmonary cysts, are useful in establishing this diagnosis.

Index terms: Angiomyolipoma, 81.3141 • Kidney neoplasms, CT, 81.12111, 81.12112, 81.3141, 81.3199 • Kidney neoplasms, US, 81.1298, 81.3141, 81.3199 • Liver neoplasms, 761.3141 • Lung, CT, 60.12111, 60.12112, 60.319, 60.829 • Lung, diseases, 60.799 • Lymphangiomyomatosis, 993.829 • Lymphatic system, CT, 99.12911, 99.12912, 99.12918 • Lymphatic system, US, 99.12983, 99.12984

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Lymphangioleiomyomatosis (LAM), a rare idiopathic disorder found almost exclusively in premenopausal women, is characterized by a proliferation of abnormal smooth muscle cells in the lungs and in the lymphatic system of the thorax and retroperitoneum (1–5). The classic triad of chest radiographic findings includes a reticular interstitial pattern, chylous pleural effusion, and recurrent pneumothoraces (6). The interstitial changes at chest radiography represent the superimposition of the thin-walled cysts that are a hallmark of LAM on computed tomographic (CT) scans (7). Although the radiologic pulmonary findings in patients with LAM have been well described, to our knowledge the abdominal imaging findings have not been described comprehensively (1,7,8). The purpose of our study was to report the abdominal CT and ultrasonographic (US) findings in 80 patients with LAM and to relate the prevalence of the findings to the severity of lung disease.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Study Population
Eighty women with pulmonary LAM who ranged in age from 27 to 70 years (mean age, 43 years) were enrolled consecutively from December 1995 to May 1998 in a natural history protocol approved by the Institutional Review Board of the National Heart, Lung, and Blood Institute. All were informed of the risks and benefits of the study and provided written informed consent. Informed consent was obtained for history and physical examinations, for laboratory tests, for pulmonary function tests, for fiberoptic or thorascopic bronchoscopy, and for radiologic studies.

The diagnosis of LAM was established with previous open-lung biopsy (50 patients), transbronchial biopsy (14 patients), or retroperitoneal lymph node biopsy (six patients) findings of replacement with abnormal smooth muscle. Only 10 patients underwent neither lung nor retroperitoneal biopsy; all 10 had characteristic pulmonary findings of LAM at thin-section CT. Seven of these 10 patients had a history of pneumothorax; of these, one had a history of chylothorax, and three had a history of biopsy-proved renal angiomyolipoma (AML). Of the remaining three, one patient had a history of chylothorax, and another had characteristic findings of retroperitoneal lymphangiomyoma.

Imaging Examinations
CT of the chest, abdomen, and pelvis was performed at our institution in every patient by using either a HiSpeed Advantage or a CT/i scanner (GE Medical Systems, Milwaukee, Wis), with 10-mm collimation at 1.0-cm intervals after the oral (1,250 mL of diatrizoate meglumine [Gastroview; Mallinckrodt, St Louis, Mo]) and intravenous (130 mL of ioxilan [Oxilan; Cook Imaging, Bloomington, Ind]) administration of nonionic contrast material at 2.0 mL/sec. The kidneys were scanned contiguously with 5-mm collimation before and after the intravenous administration of nonionic contrast material. Five patients did not receive intravenous contrast material because of a history of allergy to contrast material.

Thin-section CT of the chest was performed during the same visit; images were obtained with 1.0-mm collimation at 3-cm intervals during end inspiration, with the patient in a supine position. The images were reconstructed by using a thin-section algorithm.

Gray-scale US of the liver and kidneys and color Doppler US of the kidneys were performed at our institution in every patient during the same visit as CT, with a 128-XP unit (Acuson, Mountain View, Calif). One patient with a large abdominopelvic lymphangiomyoma also underwent pelvic US.

Medical History and Review of Previous Medical History
All patients were interviewed (J.A.K., S.C.C.) and were questioned about manifestations of LAM, which included pain, abdominal swelling, leg swelling, chyluria, and chylous vaginal discharge. Because of the known association between LAM and tuberous sclerosis complex (TSC), all patients were questioned about family histories of lung disease, pneumothoraces, skin lesions, and seizures. Patients were also examined for skin manifestations of TSC. Histopathologic reports from prior abdominal surgeries and from biopsies performed at outside institutions were reviewed (J.A.K., S.C.C.) after the prospective readings of the CT scans and US images and the recording of the findings.

Image Analysis
The images were reviewed prospectively by a board-certified radiologist (N.A.A.), who was aware of the patients' diagnoses of LAM but not of other radiologic data or of clinical or pulmonary function test findings. Chest and abdominal CT scans were obtained on the same day and were reviewed simultaneously.

Size and attenuation were measured in all masses. CT attenuation was measured by placing a region-of-interest cursor over the tissue and by calculating the mean attenuation in Hounsfield units with software available with the CT scanners. Tissue was considered to be fatty when the attenuation value was 10 HU or lower. Masses were considered to be solid if they contained fatty areas (10 HU) or enhanced. Renal and hepatic masses that contained fatty elements in accordance with CT criteria were diagnosed as AMLs.

On US images, renal and hepatic lesions were categorized according to size, echogenicity, and vascularity on color Doppler US images. Masses were determined to be cystic or solid in accordance with standard US criteria. Masses that were echogenic on US images were categorized as solid lesions.

Abdominal lymph node size and attenuation were documented with CT. The contents of lymphatic masses on CT scans were characterized as fluid or as solid on the basis of their attenuation. Homogeneous areas with attenuation of 0–25 HU were interpreted as fluid; the remainder, as solid. Round and/or elliptic solid masses were interpreted as lymph nodes. Short-axis diameters of 0.6 cm, 1.0 cm, and 1.5 cm were the cutoff criteria for lymph node enlargement in the retrocrural space, upper abdomen, and pelvis, respectively (9). Elongated or tubular masses with central areas of low attenuation encapsulated by a thin wall or by a rind of soft-tissue attenuation were interpreted as lymphangiomyomas.

The severity of lung disease was determined with visual inspection of thin-section CT scans of the chest and received one of three grades: I (mild), if pulmonary cysts involved less than one-third of the lung parenchyma; II (moderate), if pulmonary cysts involved one-third to two-thirds of the lung parenchyma; or III (severe), if pulmonary cysts involved two-thirds or more of the lung parenchyma or if the patient already had undergone lung transplantation (Fig 1). This represents a variation of the methods used by Muller et al (10) and by Aberle et al (6). Cochran-Armitage and ² tests were performed to assess the association between the severity of lung disease and enlarged abdominal lymph nodes and renal lesions (11,12). A P value of .05 (² or Cochran-Armitage test, respectively) was considered to indicate a significant difference.

View larger version (126K): [in this window] [in a new window] [Download PPT slide]   Figure 1a. Nonenhanced thin-section CT scans of the chest (1-mm-thick sections) demonstrate the extent of pulmonary disease in patients with LAM. (a) Transverse scan in a 34-year-old patient with LAM with grade I pulmonary involvement shows scattered pulmonary cysts (arrows) that involve less than one-third of the parenchyma. (b) Transverse scan in a 28-year-old patient with LAM with grade II pulmonary involvement shows diffuse pulmonary cysts that involve one-third to two-thirds of the lung parenchyma. (c) Transverse scan in a 27-year-old patient with LAM with grade III pulmonary involvement shows diffuse pulmonary cysts that involve more than two-thirds of the parenchyma and shows very little normal lung.

View larger version (104K): [in this window] [in a new window] [Download PPT slide]   Figure 1b. Nonenhanced thin-section CT scans of the chest (1-mm-thick sections) demonstrate the extent of pulmonary disease in patients with LAM. (a) Transverse scan in a 34-year-old patient with LAM with grade I pulmonary involvement shows scattered pulmonary cysts (arrows) that involve less than one-third of the parenchyma. (b) Transverse scan in a 28-year-old patient with LAM with grade II pulmonary involvement shows diffuse pulmonary cysts that involve one-third to two-thirds of the lung parenchyma. (c) Transverse scan in a 27-year-old patient with LAM with grade III pulmonary involvement shows diffuse pulmonary cysts that involve more than two-thirds of the parenchyma and shows very little normal lung.

View larger version (123K): [in this window] [in a new window] [Download PPT slide]   Figure 1c. Nonenhanced thin-section CT scans of the chest (1-mm-thick sections) demonstrate the extent of pulmonary disease in patients with LAM. (a) Transverse scan in a 34-year-old patient with LAM with grade I pulmonary involvement shows scattered pulmonary cysts (arrows) that involve less than one-third of the parenchyma. (b) Transverse scan in a 28-year-old patient with LAM with grade II pulmonary involvement shows diffuse pulmonary cysts that involve one-third to two-thirds of the lung parenchyma. (c) Transverse scan in a 27-year-old patient with LAM with grade III pulmonary involvement shows diffuse pulmonary cysts that involve more than two-thirds of the parenchyma and shows very little normal lung.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Sixty-one (76%) of 80 patients with LAM had positive abdominal CT or US findings or both. Common abdominal findings included renal AMLs in 43 (54%) of 80 patients, enlarged abdominal lymph nodes in 31 (39%), and lymphangiomyoma in 13 (16%) (Table).

View larger version (107K): [in this window] [in a new window] [Download PPT slide]   Figure 2a. CT and US images in a 37-year-old patient with a single renal AML. (a) Nonenhanced, transverse, 5-mm-thick CT scan demonstrates a 7-cm mass (arrow) that arises from the upper pole of the right kidney; the mass contains low-attenuating areas consistent with fat. (b) Contrast-enhanced, transverse, 5-mm-thick CT scan shows partial enhancement (arrow) of the renal mass in a. (c) Longitudinal US image of the renal mass in a and b shows that the mass (electronic calipers) is markedly echogenic.

View larger version (104K): [in this window] [in a new window] [Download PPT slide]   Figure 2b. CT and US images in a 37-year-old patient with a single renal AML. (a) Nonenhanced, transverse, 5-mm-thick CT scan demonstrates a 7-cm mass (arrow) that arises from the upper pole of the right kidney; the mass contains low-attenuating areas consistent with fat. (b) Contrast-enhanced, transverse, 5-mm-thick CT scan shows partial enhancement (arrow) of the renal mass in a. (c) Longitudinal US image of the renal mass in a and b shows that the mass (electronic calipers) is markedly echogenic.

View larger version (100K): [in this window] [in a new window] [Download PPT slide]   Figure 2c. CT and US images in a 37-year-old patient with a single renal AML. (a) Nonenhanced, transverse, 5-mm-thick CT scan demonstrates a 7-cm mass (arrow) that arises from the upper pole of the right kidney; the mass contains low-attenuating areas consistent with fat. (b) Contrast-enhanced, transverse, 5-mm-thick CT scan shows partial enhancement (arrow) of the renal mass in a. (c) Longitudinal US image of the renal mass in a and b shows that the mass (electronic calipers) is markedly echogenic.

View larger version (108K): [in this window] [in a new window] [Download PPT slide]   Figure 3a. CT scans in a 32-year-old patient with multiple renal AMLs. (a) Nonenhanced, transverse, 5-mm-thick scan demonstrates three separate fatty masses (arrows) that arise from the left kidney. (b) Contrast-enhanced, transverse, 5-mm-thick scan obtained at the same level as a shows heterogeneous enhancement of the renal lesions (arrows).

View larger version (110K): [in this window] [in a new window] [Download PPT slide]   Figure 3b. CT scans in a 32-year-old patient with multiple renal AMLs. (a) Nonenhanced, transverse, 5-mm-thick scan demonstrates three separate fatty masses (arrows) that arise from the left kidney. (b) Contrast-enhanced, transverse, 5-mm-thick scan obtained at the same level as a shows heterogeneous enhancement of the renal lesions (arrows).

Ten patients had 12 solid, contrast material–enhancing renal masses (size range, 0.5–3.5 cm in diameter) that had no demonstrable fat at CT and either were not seen or were not echogenic at US. These lesions were thought to represent either atypical AMLs or other renal neoplasms. Biopsy was performed at our institution in one lesion that was found to be an AML (Fig 4). Of the remaining nine patients with atypical lesions, one showed no interval change at 18-month follow-up, six showed no interval change at 1-year follow-up, one showed no interval change at 8-month follow-up, and one patient had yet to return for 6-month follow-up at the time this study was concluded.

View larger version (132K): [in this window] [in a new window] [Download PPT slide]   Figure 4a. CT and US images in a 51-year-old patient with LAM show the atypical appearance of core-needle biopsy-proved renal AML. (a) Transverse US image shows a solid mass (arrow) that arises from the upper pole of the left kidney. The mass is isoechoic to renal parenchyma. (b) Nonenhanced, transverse, 5-mm-thick CT scan demonstrates the renal mass (arrow) in a. The renal mass is isoattenuating compared with renal parenchyma. (c) Contrast-enhanced, transverse, 5-mm-thick CT scan demonstrates slight enhancement of the renal mass (straight arrow) relative to the normal renal parenchyma. Also shown is a paraaortic lymph node (curved arrow).

View larger version (129K): [in this window] [in a new window] [Download PPT slide]   Figure 4b. CT and US images in a 51-year-old patient with LAM show the atypical appearance of core-needle biopsy-proved renal AML. (a) Transverse US image shows a solid mass (arrow) that arises from the upper pole of the left kidney. The mass is isoechoic to renal parenchyma. (b) Nonenhanced, transverse, 5-mm-thick CT scan demonstrates the renal mass (arrow) in a. The renal mass is isoattenuating compared with renal parenchyma. (c) Contrast-enhanced, transverse, 5-mm-thick CT scan demonstrates slight enhancement of the renal mass (straight arrow) relative to the normal renal parenchyma. Also shown is a paraaortic lymph node (curved arrow).

View larger version (132K): [in this window] [in a new window] [Download PPT slide]   Figure 4c. CT and US images in a 51-year-old patient with LAM show the atypical appearance of core-needle biopsy-proved renal AML. (a) Transverse US image shows a solid mass (arrow) that arises from the upper pole of the left kidney. The mass is isoechoic to renal parenchyma. (b) Nonenhanced, transverse, 5-mm-thick CT scan demonstrates the renal mass (arrow) in a. The renal mass is isoattenuating compared with renal parenchyma. (c) Contrast-enhanced, transverse, 5-mm-thick CT scan demonstrates slight enhancement of the renal mass (straight arrow) relative to the normal renal parenchyma. Also shown is a paraaortic lymph node (curved arrow).

View larger version (123K): [in this window] [in a new window] [Download PPT slide]   Figure 5a. Ten-millimeter-thick CT scans in a 53-year-old patient with LAM demonstrate multiple abdominal enlarged lymph nodes. The patient underwent surgical biopsy; findings showed replacement of the normal lymph node architecture with smooth muscle cells. (a) Nonenhanced transverse CT scan in the abdomen shows a 1.4-cm paraaortic lymph node (arrow), with a central area of low-attenuating material. (b) Contrast-enhanced transverse CT scan shows enhancement of the peripheral portion of the lymph node (arrow) in a.

View larger version (121K): [in this window] [in a new window] [Download PPT slide]   Figure 5b. Ten-millimeter-thick CT scans in a 53-year-old patient with LAM demonstrate multiple abdominal enlarged lymph nodes. The patient underwent surgical biopsy; findings showed replacement of the normal lymph node architecture with smooth muscle cells. (a) Nonenhanced transverse CT scan in the abdomen shows a 1.4-cm paraaortic lymph node (arrow), with a central area of low-attenuating material. (b) Contrast-enhanced transverse CT scan shows enhancement of the peripheral portion of the lymph node (arrow) in a.

View larger version (140K): [in this window] [in a new window] [Download PPT slide]   Figure 6a. CT and US images in a 37-year-old patient who had diffuse, low-attenuating retroperitoneal masses consistent with dilatation of the abdominal lymph vessels or with lymphangiomyoma. (a) Contrast-enhanced, 10-mm-thick transverse CT scan in the upper abdomen obtained at the level of the kidneys demonstrates a large (maximum transverse diameter, 9.0 cm), low-attenuating, multilobulated mass (arrow), consistent with a lymphangiomyoma, that elevates the great vessels away from the spine. (b) Contrast-enhanced, 10-mm-thick transverse CT scan in the pelvis shows extension of the confluent lymphangiomyoma (arrow) into the right side of the pelvis. (c) Coronal US image in the abdomen demonstrates the lymphangiomyoma in a and b and demonstrates multiple septations (arrow) and central hypoechoic areas.

View larger version (125K): [in this window] [in a new window] [Download PPT slide]   Figure 6b. CT and US images in a 37-year-old patient who had diffuse, low-attenuating retroperitoneal masses consistent with dilatation of the abdominal lymph vessels or with lymphangiomyoma. (a) Contrast-enhanced, 10-mm-thick transverse CT scan in the upper abdomen obtained at the level of the kidneys demonstrates a large (maximum transverse diameter, 9.0 cm), low-attenuating, multilobulated mass (arrow), consistent with a lymphangiomyoma, that elevates the great vessels away from the spine. (b) Contrast-enhanced, 10-mm-thick transverse CT scan in the pelvis shows extension of the confluent lymphangiomyoma (arrow) into the right side of the pelvis. (c) Coronal US image in the abdomen demonstrates the lymphangiomyoma in a and b and demonstrates multiple septations (arrow) and central hypoechoic areas.

View larger version (110K): [in this window] [in a new window] [Download PPT slide]   Figure 6c. CT and US images in a 37-year-old patient who had diffuse, low-attenuating retroperitoneal masses consistent with dilatation of the abdominal lymph vessels or with lymphangiomyoma. (a) Contrast-enhanced, 10-mm-thick transverse CT scan in the upper abdomen obtained at the level of the kidneys demonstrates a large (maximum transverse diameter, 9.0 cm), low-attenuating, multilobulated mass (arrow), consistent with a lymphangiomyoma, that elevates the great vessels away from the spine. (b) Contrast-enhanced, 10-mm-thick transverse CT scan in the pelvis shows extension of the confluent lymphangiomyoma (arrow) into the right side of the pelvis. (c) Coronal US image in the abdomen demonstrates the lymphangiomyoma in a and b and demonstrates multiple septations (arrow) and central hypoechoic areas.

View larger version (141K): [in this window] [in a new window] [Download PPT slide]   Figure 7. Contrast-enhanced, 10-mm-thick transverse CT scan in a 45-year-old patient demonstrates paracentesis-proved chylous ascites (A), which had an attenuation of -10 HU. The patient also had associated thoracentesis-proved chylous pleural effusion and biopsy-proved retroperitoneal adenopathy that showed the replacement of the normal lymph node architecture with smooth muscle.

View larger version (88K): [in this window] [in a new window] [Download PPT slide]   Figure 8. Contrast-enhanced, 10-mm-thick transverse CT scan of the upper abdomen in a 46-year-old patient demonstrates a low-attenuating, tubular structure (arrow) that courses along the right paraspinal space; this structure represents diffuse dilatation of the thoracic duct.

View larger version (107K): [in this window] [in a new window] [Download PPT slide]   Figure 9a. CT and US images obtained in the liver of a 30-year-old patient with biopsy-proved hepatic AML. (a) Contrast-enhanced, 10-mm-thick transverse CT scan demonstrates multiple hepatic masses (arrows) with markedly low attenuation. (b) Sagittal US image demonstrates the dominant mass in a, which is hyperechoic (arrow) relative to the normal hepatic parenchyma.

View larger version (153K): [in this window] [in a new window] [Download PPT slide]   Figure 9b. CT and US images obtained in the liver of a 30-year-old patient with biopsy-proved hepatic AML. (a) Contrast-enhanced, 10-mm-thick transverse CT scan demonstrates multiple hepatic masses (arrows) with markedly low attenuation. (b) Sagittal US image demonstrates the dominant mass in a, which is hyperechoic (arrow) relative to the normal hepatic parenchyma.

Sixteen patients had abdominal symptoms related to LAM. Nine patients had complications related to renal AMLs. Eight had chronic flank pain and hematuria due to intratumoral hemorrhage and underwent nephrectomy. One patient had hematuria and flank pain that resolved spontaneously. Three of seven patients with ascites detected at imaging had bloating that was attributable to their ascites. Four other patients had chronic abdominal discomfort that was thought to be related to retroperitoneal lymphangioleiomyoma.

All 80 patients denied any family history or signs or symptoms of TSC.

Correlation of Abdominopelvic Imaging Findings with Severity of Lung Disease
The severity of lung disease at presentation was as follows: grade I, 21 (26%) of 80 patients; grade II, 23 (29%) of 80 patients; and grade III, 36 (45%) of 80 patients. Five of the 36 patients with grade III disease had undergone lung transplantation.

There was a significant monotonic relationship between the severity of lung involvement and the enlargement of the abdominal lymph nodes. Patients with more severe lung disease were found more frequently to have enlarged abdominal lymph nodes than were patients with less severe lung disease (Cochran-Armitage test, P = .02). Enlarged abdominal lymph nodes were found in four (19%) of 21 patients with grade I lung disease, in seven (30%) of 23 patients with grade II lung disease, and in 20 (56%) of 36 patients with grade III lung disease.

A positive linear trend was observed between the probability of a renal mass and the severity of lung disease. Renal masses were observed in 43% of patients with grade I lung disease, in 52% of patients with grade II lung disease, and in 61% of patients with grade III lung disease. However, this was not significant (² test, P = .4; Cochran-Armitage test, P = .2). The probability that patients with renal masses had multiple masses varied among the lung disease severity grades (² test, P = .02); however, no trend was observed between this probability and the severity of lung disease. Multiple renal masses were observed in two (22%) of nine patients with a renal mass and with grade I lung disease, in nine (75%) of 12 patients with a renal mass and with grade II lung disease, and in seven (32%) of 22 patients with a renal mass and with grade III lung disease.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
The four major abdominopelvic abnormalities in patients with LAM include renal AML, lymphadenopathy, lymphangiomyoma, and chylous ascites (7,8,13,14). To the best of the authors' knowledge, this article describes the largest series of abdominopelvic imaging findings in patients with LAM and is the only one in which abdominopelvic findings are compared with the severity of lung disease.

Renal AML, also called renal hamartoma, is the most common tumor associated with LAM (8). Thin-section, nonenhanced CT is essential to visualize the fat content of AMLs. Careful focal sampling of the low-attenuating regions within the mass must be performed, since the masses frequently are heterogeneous. A single region of interest over the entire tumor may produce mean attenuation in the nonfatty soft-tissue range; thus, the fat may not be detected (15). Helical CT is more sensitive than conventional CT in demonstrating the fat in AMLs less than 2 cm in diameter (16).

A major complication of renal AML is hemorrhage, which may manifest as flank pain or shock (4). The recommended management of renal AML is based on tumor size and symptoms (17). Patients with asymptomatic lesions that are smaller than 4.0 cm in diameter may be followed up with annual US or CT. Patients with lesions of 4.0 cm or greater in diameter should be followed up with semiannual US or CT. Eight patients in our series underwent emergency nephrectomy because of progressive symptoms. Knowledge of the proclivity of patients with LAM to develop renal AMLs may be helpful in guiding therapy. If a patient with renal pain or hematuria is known to have a renal AML, then partial nephrectomy or embolization should be considered rather than a more radical procedure (17).

Our results show that either CT or US alone may not be sufficient to depict renal AMLs. US failed to depict 20 of 85 solid renal masses, while CT failed to depict nine of 85. US failed to depict the AMLs if they were isoechoic to normal renal parenchyma and did not deform the renal contour or if they were adjacent to normal renal sinus fat. CT failed to depict some lesions possibly because of partial volume artifact. We were able to diagnose even small AMLs less than 1.0 cm in diameter; fat within the AML at CT or hyperechoic texture at US made it relatively easy to recognize these lesions.

In our series, 31 (39%) of 80 patients had abdominal lymphadenopathy. The adenopathy may be extensive; some of the lymph nodes in our series measured up to 4.0 cm in diameter. Although a majority of our patients with adenopathy did not undergo biopsy, all patients who underwent biopsy demonstrated replacement of the lymph nodes with smooth muscle. Some lymph nodes contained low-attenuating (-72 to 50 HU) areas at CT that were hypoechoic at US. We suspect that such low Hounsfield units indicate chylous lymph collections or fat within the lymph nodes, although we have no direct histopathologic proof of the latter. We found a significant positive trend (Cochran-Armitage test, P = .02) between the severity of lung disease and the presence of abdominal adenopathy; the probability of adenopathy increased with the severity of lung disease. This is not surprising, since, in patients with LAM, lung involvement and abdominal adenopathy are related to disorders of the lymphatic system.

Lymphangioleiomyomas result from the proliferation of smooth muscle cells in the lymph vessels, which causes dilatation and obstruction in the lymph vessels and results in cystic collections of chylous material (5,18–21). This process is similar to the observed obstruction and dilatation of the thoracic duct in patients with LAM. At CT, the dilated retroperitoneal lymph vessels may have either thin or thick walls and may contain material low in attenuation (3–25 HU). These features may be explained as a mechanical complication of lymphatic obstruction and of the disruption of lymphatic flow.

Lymphangioleiomyomas may lie between and displace vascular structures in the retroperitoneum and, along with abdominal adenopathy, may be misdiagnosed as a neoplastic process such as lymphoma. Indeed, in this series, six patients received a diagnosis of LAM only after retroperitoneal lymph node biopsy to exclude lymphoma. Overdistention of lymph cysts may result in rupture and chylous ascites. This complication is well demonstrated in an article (22) on a patient in whom the onset of ascites was accompanied by a marked decrease in the size of the cystic retroperitoneal masses.

Although this is a discussion of LAM, a discussion of TSC is in order, given their similarities. LAM can occur without other disease ("sporadic" LAM) or in association with TSC (23). TSC is an autosomal-dominant genetic disorder with pulmonary, renal, and lymph node findings similar to those of LAM. It is thought that LAM may be a "forme fruste" of TSC (24,25). A hallmark of TSC is the presence of multiple renal AMLs, which occur in about 40%–80% of patients (mostly female) and which usually are bilateral. In our series, 43 (54%) of 80 patients with LAM had solid renal masses; these were multiple in 18 (23%) of 80 patients. Although AMLs occur in patients of either sex with TSC, cystic lung disease is found only in women (26). Patients with LAM do not have the brain and skin findings associated with TSC (cortical tubers, subependymal nodules, retinal hamartomas, facial angiofibromas, or periungual fibromas) (27).

At the time this article was written, to our knowledge there is no increased prevalence of renal cancer reported in patients with LAM, whereas patients with TSC have an increased risk of renal cell carcinoma (1%–2%) and clear cell carcinoma (28,29). Specific genetic abnormalities in chromosome band 9q34 (TSC1) or in chromosome band 16p13 (TSC2) have been discovered in individuals with TSC (30,31). Although no genetic defect has been discovered in patients with LAM, some AMLs and abdominal lymph nodes in women with LAM and the women themselves have a loss of heterozygosity in chromosome band 16p13; this finding is similar to that seen in patients with TSC and suggests that LAM may be caused by mutations of the TSC2 gene (23).

The principal limitation of this study was the lack of histopathologic correlation of CT and US findings in a majority of cases. Such a standard, of course, is not possible or ethical in this type of study. Thus, for example, it is unclear whether small renal AMLs were missed with both modalities and if their prevalence was underestimated.

There are several abdominal imaging findings in patients with LAM (renal AML, enlarged lymph nodes, and lymphangiomyoma) that, in conjunction with the classic thin-section CT finding of pulmonary cysts, should help to support the radiologic diagnosis of this disease.

	FOOTNOTES

 
Abbreviations: AML = angiomyolipoma, LAM = lymphangioleiomyomatosis, TSC = tuberous sclerosis complex

Author contributions: Guarantor of integrity of entire study, N.A.A.; study concepts and design, N.A.A.; definition of intellectual content, N.A.A.; literature research, N.A.A.; clinical studies, J.A.K., S.C.C., J.M.; data acquisition, J.A.K., S.C.C., N.A.A.; data analysis, A.J.D.; statistical analysis, A.J.D.; manuscript preparation, N.A.A.; manuscript editing, S.C.C., J.A.K., J.M., A.J.D.; manuscript review, J.M., A.J.D.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 

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