Answer: Angiomyolipoma

Histology: The tissue consists predominantly of adipose tissue. The adipose tissue lacks atypia or lipoblasts. Focally, clusters of spindle cells with eosinophilic cytoplasm can be identified, consistent with a smooth muscle component. Rare abnormal thick walled vessels can be seen.

Discussion: A typical angiomyolipoma consists of three components, which include thick wall vessels, smooth muscle cells and adipose tissue. However, variation in the proportion of the components may be seen in various tumors. In this case the adipose tissue predominates. As the adipose tissue in this case lacks atypia or lipoblasts and shows focal clusters of eosinophilic smooth muscle cells, liposarcoma and normal adipose tissue are unlikely. Immunohistochemical stains are helpful in differentiating these lesions. Angiomyolipoma is intensely positive upon immunostaining with HMB45.

20% to 50% of angiomyolipomas are seen in association with patients who have tuberous sclerosis. Angiomyolipomas may present in multiple locations, including lymph nodes, which is thought to represent multi-focal disease rather than metastasis. The majority of angiomyolipomas are benign lesions and do not metastasize. However, there are rare reported cases of angiomyolipomas with malignant behavior, usually with an epithelioid morphology. In cases of epithelioid angiomyolipomas, the issue should be raised to the clinician that, although many cases with similar histology have not behaved aggressively, this histology may rarely be associated with aggressive behavior.

Reference(s):
L’hostis H, Deminiere C, Ferriere JM, Coindre JM. Renal angiomyolipoma: a clinical pathologic immunohistochemical and follow-up study of 46 cases. Amer Jnl Surg Path; 1999; 23: 1011-1020.