[791] Renal Angiomyolipoma in the First Two Decades of Life: A Clinicopathologic Study of 44 Cases

JB Keylock, JC Fanburg-Smith, R Alaggio, JH Barton, IS Sesterhenn. Armed Forces Institute of Pathology, Washington, DC; University of Padova, Padova, Italy

Background: Angiomyolipoma (AML) is derived from the perivascular epithelioid cells (PEC) and part of the PEComa family. AML occur both sporadically and in association with tuberous sclerosis (TS). Although most AML are discovered and diagnosed in adults, this series reviews the clinicopathologic features of renal AML in the first two decades.
Design: 66 cases of PEComa family tumors in patients, <21 years of age, were pulled from our files. The study was confined to renal AML with available material.
Results: 44 pediatric renal AML were included. Patient ages ranged from 8-20 years (mean age 16). 42% were male, 58% female. Of patients with known clinical history, 38% had a definite or suspected diagnosis of TS. Four patients presented with retroperitoneal hemorrhage, three with flank pain. AML had a nearly equal predilection for kidney side. Tumor sizes ranged from 1.8 cm- 25 cm, mean 11.6 cm. Microscopically, the main mass separable from surrounding renal parenchyma, and predominantly (n=32) spindled smooth muscle rather than epithelioid . The smooth muscle component compared with fat ranged from 10% to nearly 100%, with more than half composed of >90% smooth muscle. Findings included necrosis (n=11), pleomorphism (n=15), regional lymph node involvement (n=3), coexisting oncocytic neoplasm (n=1), coexisting renal cell carcinoma (n=1), hemorrhage (n=15), prominent collagen (n=10), hemangiopericytoma-like vascular pattern (n=7), multinucleation (n=8), myxoid myointimal proliferation (n=8), prominent nucleoli (n=5), increased cellularity (n=6), and nuclear pseudoinclusions (n=2). None had easily identified mitotic activity. Multifocal angiomyolipoma (n=17) and microscopic cysts mostly corresponded to known TS patients. Concurrent extrarenal tumors included AML of adrenal gland (n=1), lymphangioleiomyomatosis of lung (n=1), and PEComa of unknown site (n=1). All cases studied were positive for HMB45, actin, and desmin33. There were no known metastases.
Conclusions: Pediatric myomelanocytic tumors are mostly renal AML that occur in teenagers with equal sex distribution, 38% associated with TS. The latter patients often have multifocal AML. Similar to adults, these tumors can be symptomatic with hemorrhage or flank pain or discovered incidentally. Pediatric renal AML are mostly composed of spindled smooth muscle, with little fat or epithelioid change. Necrosis, atypia, multifocality or lymph node involvement do not necessarily indicate malignancy.
Category: Genitourinary (including renal tumors)

Wednesday, March 11, 2009 1:00 PM

Poster Session VI # 132, Wednesday Afternoon