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RESIDENT CASE STUDIES

Week 5 May 19 - May 23, 2003: Case 2  

Table of Contents | List of Diagnoses | Case 1 | Case 2 | Case 3 | Case 4

28 year old female with history of tuberous sclerosis, with a large (>20 cm in diameter) retroperitoneal mass

Discussion:
Angiomyolipoma (AML) is a benign tumor of the kidney characterized by a mixture of smooth muscle, fat and thick walled blood vessels. AML is generally asymptomatic, but can manifest as abdominal pain, palpable mass or hematuria. Approximately 50% of the cases are associated with tuberous sclerosis. Cases associated with tuberous sclerosis are diagnosed earlier than sporadic cases (median age 25 vs. 45 years). Malignant transformation has been described, but this is exceedingly rare (1,2). Involvement of regional lymph nodes, renal vein or spleen may occur and should not be taken as a sign of malignant tumor, but of the multicentricity of the tumor (3). According to De Pauw et al. (4) renal AML represents the most frequent extrapulmonary manifestation of pulmonary lymphangioleiomyomatosis (LAM). Renal AML is found in 32% to 60 % of pulmonary LAM cases in which a systematic search with abdominal computed tomography (CT) scan is done (4). Histologically AML is a triphasic tumor with smooth muscle, adipose tissue and thick walled blood vessels in varying proportion. It is important to note that nuclear pleomorphism, necrosis and mitosis may be seen in benign AML (5). The smooth muscle may occasionally have an epithelioid appearance. The smooth muscle component of AML stains positive for vimentin, actin and desmin. AML appears to stain for HMB 45 in almost all cases.

Complications from angiomyolipomas are rare, but often severe depending on the size and content of the angiomyolipoma. This may present as renal colic, retroperitoneal hemorrhage or perinephric hemorrhage, due to rupture (6,7). AML may also be associated with Wunderlich’s syndrome - spontaneous renal bleeding confined to the subcapsular and perirenal space (8).

The most important differential diagnosis is with malignant spindle cell tumors of kidney or retroperitoneal origin, but these do not usually have the thick walled vessels. In addition, sarcoma and sarcomatoid carcinoma can have overlapping features with atypical AML but usually occur in older age groups, lack HMB45 reactivity, and lack fatty component.  

References:

  1. Takahashi N, Kitahara R, Hishimoto Y, et al. Malignant transformation of renal angiomyolipoma. Int J Urol 2003 May;10(5):271-273.

  1. Martignoni G, Pea M, Rigaud G, et al. Renal angiomyolipoma with epithelioid sarcomatous transformation and metastases: demonstration of the same genetic defects in the primary and metastatic lesions. Am J Surg Pathol 2000 Jun;24(6):889-94.

  1. Turker Koksal I, Tunc M, Kilicaslan I, et al. Lymph nodal involvement by renal angiomyolipoma. Int J Urol 2000 Oct;7(10):386-9.

  1. De Pauw RA, Boelaert JR, Haenebalcke CW, et al. Renal angiomyolipoma in association with pulmonary lymphangioleiomyomatosis. Am J Kidney Dis 2003 Apr;41(4):877-83.

  1. Hartwick RWJ, Srigley J, Shaw P. Uncommon histologic patterns mimicking malignancy in angiomyolipoma, abstracted. Lab Invest 60:39A, 1985.

  1. Derchi LE, Zappasodi F, Busilacchi P, et al. Spontaneous rupture of renal angiomyolipoma with   perinephric haemorrhage: sonographic findings. Br J Radiol 1985 Oct;58(694):979-82.

  1. Wolfe TR. Ruptured renal angiomyolipoma presenting as renal colic. Am J Emerg Med 1998 Nov;16(7):658-61.

  1. Albi G, del Campo L, Tagarro D. Wunderlich's syndrome: causes, diagnosis and radiological management. Clin Radiol 2002 Sep;57(9):840-5.