(Radiographics. 1999;19:555-558.)
© RSNA, 1999
US Case of the Day
Timothy C. Carter, MD1,
Teresita L. Angtuaco, MD1 and
Hemendra R. Shah, MD1
1 Department of Radiology, University of Arkansas for Medical Sciences, 4301 W Markham, Slot 556, Little Rock, AR 72205
Index Terms: Kidney neoplasms, 81.3141 • Kidney neoplasms, diagnosis, 81.3141 • Lipoma and lipomatosis, 81.3141 • Sclerosis, tuberous, **.18322
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HISTORY
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A woman with multiple cutaneous lesions and an unspecified seizure disorder first presented to our department at age 19 years for documentation of bilateral renal masses that had been discovered several years earlier. An ultrasound (US) examination and both unenhanced and contrast material–enhanced computed tomography (CT) were performed. Five years later, the patient (now age 24 years) presented to the emergency department with complaints of acute left flank pain, nausea, vomiting, and hematuria. Repeat US and contrast-enhanced CT were performed.
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FINDINGS
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US images obtained at initial presentation revealed heterogeneous, predominantly echogenic masses in the expected locations in both kidneys (Fig 1). No normal-appearing renal parenchyma was seen. CT better demonstrated the size and make-up of the renal masses, showing focal collections of fat dispersed among other solid but contrast-enhanced elements (Fig 2).
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Figure 2a. Axial unenhanced (a) and contrast-enhanced (b) CT scans of the kidneys show large bilateral renal masses (arrows) containing large foci of fat interspersed with other solid but contrast-enhanced elements.
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Figure 2b. Axial unenhanced (a) and contrast-enhanced (b) CT scans of the kidneys show large bilateral renal masses (arrows) containing large foci of fat interspersed with other solid but contrast-enhanced elements.
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Five years later, changes in the composition of the left renal mass were identified at both repeat US and contrast-enhanced CT. These changes correlated with the clinical manifestation of acute left flank pain and hematuria. Conventional and color Doppler US showed a complex cystic structure containing areas of arterial vascular flow within the upper pole of the affected kidney (Fig 3). CT demonstrated intratumoral hematoma and focal enhancement, consistent with a large pseudoaneurysm (Fig 4).
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Figure 3. Black and white reproduction of a color Doppler US image of the left kidney obtained during an episode of acute flank pain and hematuria demonstrates arterial flow (arrows) and thrombus (arrowheads) within a new intratumoral pseudoaneurysm.
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Figure 4a. Axial unenhanced (a) and contrast-enhanced (b) CT scans of the kidneys obtained immediately after color Doppler US examination (cf Fig 3) show bilateral intratumoral hematomas (arrows in a) and focal areas of dense contrast enhancement (arrows in b) associated with pseudoaneurysm formation.
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Figure 4b. Axial unenhanced (a) and contrast-enhanced (b) CT scans of the kidneys obtained immediately after color Doppler US examination (cf Fig 3) show bilateral intratumoral hematomas (arrows in a) and focal areas of dense contrast enhancement (arrows in b) associated with pseudoaneurysm formation.
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DIAGNOSIS: Large, bilateral angiomyolipomas of the kidneys with tuberous sclerosis.
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DISCUSSION
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Angiomyolipomas are uncommon, benign tumors of the kidney composed of varying proportions of mature adipose tissue, smooth muscle cells, and blood vessels (1,2). At US, angiomyolipomas demonstrate marked increased echogenicity, which appears to be directly related to both the amount of adipose tissue within the tumor and the numerous tissue interfaces produced by blood vessels in this highly vascular lesion (3,4). Occasionally, other renal tumors may demonstrate the type of dense, increased echogenicity reported with angiomyolipomas. In addition to benign lesions such as oncocytoma, cavernous hemangioma, and renal infarction, malignancies such as renal cell carcinoma, liposarcoma, and lymphoma may be indistinguishable from angiomyolipomas at US (5). Particularly worrisome are recent reports in which approximately 30% of small (<3 cm) renal cell carcinomas were found to appear identical to angiomyolipomas of a similar size (6). To more accurately establish the diagnosis in cases involving echogenic renal masses, CT or magnetic resonance imaging is most often used to detect foci of fat, whose presence is overwhelmingly characteristic of angiomyolipoma (7–9). Rarely, tumors other than angiomyolipoma contain sufficient quantities of fat to be detected at CT. These tumors include lipoma, liposarcoma, Wilms tumor, teratoma, oncocytoma, and xanthogranulomatous pyelonephritis (10). Two cases of renal cell carcinoma have been reported in which CT revealed fat-attenuation tissue along with calcification associated with a solid renal mass (11,12). The presence of calcification in cases of suspected angiomyolipoma should prompt further evaluation with percutaneous biopsy, surgical excision, or at least follow-up CT to exclude a possible rare malignancy.
Sporadic (or isolated) angiomyolipomas account for 80%–90% of reported cases (13,14). The remaining cases of angiomyolipoma involve patients diagnosed with tuberous sclerosis, approximately 40%–80% of whom prove to have single, multiple, or bilateral angiomyolipomas of the kidneys (15). Tuberous sclerosis is a congenital syndrome with an autosomal dominant pattern of inheritance. Females are affected slightly more often than males, with the disease occurring in one of every 150,000 births (15). In addition to angiomyolipoma of the kidney, other types of hamartomas are seen that involve the brain and subcutaneous tissues (15). Retinal phacomas, cardiac rhabdomyomas, and lymphangiomyomatosis of the lungs are also seen in a large number of affected individuals.
The majority of renal angiomyolipomas are clinically silent, with sporadic cases most often detected as incidental findings during US or CT examination for unrelated causes. When symptoms do occur, the most common complaints include acute flank pain and hematuria related to spontaneous intratumoral or extrarenal hemorrhage. The fact that angiomyolipomas have a greater tendency to bleed than do other solid organ tumors seems to be related to an increase in vascularity as well as to vessel wall composition in which an incomplete elastic layer predisposes these tumors to the formation of microaneurysms (16).
Our patient developed intratumoral hemorrhage and underwent angiography, which demonstrated a large pseudoaneurysm involving a segmental artery within the upper pole of the left kidney. Although kidney-sparing surgery and complete nephrectomy are often considered in similar cases of large angiomyolipomas, a more conservative approach involving selective arterial embolization was taken in this case and met with initial success (17). The patient was discharged without further complication.
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Footnotes
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Address reprint requests to T.C.C.
** indicates multiple body systems. 
From the 1998 RSNA scientific assembly.
Received for publication October 23, 1998.
Revision received November 9, 1998. December 11, 1998.
Accepted for publication December 18, 1998.
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References
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Lemaitre L, Robert Y, Dubrulle F, et al. Renal angiomyolipoma: growth followed up with CT and/or US. Radiology 1995; 197:598-602.[Abstract/Free Full Text]
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Bissada NK, White HJ, Chao NS, Smith PL, Barbour GL, Redman JF. Tuberous sclerosis complex and renal angiomyolipoma. Urology 1975; 6:105-113.[Medline]
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HISTORY
FINDINGS
