Primary vascular tumors and tumor-like lesions of the kidney: a clinicopathologic analysis of 25 cases.

Vascular tumors of the kidney are distinctly rare, and to date no large series have been reported. We analyzed a series of primary vascular tumors of the kidney to further delineate their clinicopathologic features and identify organ-specific morphologic features, if present. Twenty-five renal cases previously coded as "arteriovenous malformation," "hemangioma," and "angiosarcoma" were retrieved from the archives of 4 collaborating institutions and were reevaluated histologically. Tumors were classified according to the 2002 World Health Organization classification of tumors of soft tissue and bone. There were 18 males and 7 females (M:F=2.6:1) ranging from 21 to 95 years (mean 56.7 y). Lesions ranged from "microscopic" to 30 cm (mean 6.0 cm) and were tan-brown, cystic, and hemorrhagic. On re-review, cases were classified as arteriovenous malformation (n=3), capillary hemangioma (n=14), and angiosarcoma (n=8). Arteriovenous malformations were identical to their somatic soft tissue counterparts. Renal capillary hemangiomas often lacked a well-formed lobular pattern and 5 cases showed a "sieve-like" arrangement reminiscent of splenic sinusoids, a pattern previously noted by others (anastomosing hemangioma). All hemangiomas were noninfiltrative and lacked cytologic atypia and mitotic activity. GLUT-1, D2-40, and CD8 were performed in 3 anastomosing hemangiomas and were all negative. Angiosarcomas were diffusely infiltrative with extensive parenchymal destruction; all showed at least small areas of conventional vasoformative growth, but were frequently dominated by spindled and epithelioid histology. All cases were positive for some combination of vascular tumor-associated markers (CD31, CD34, and FLI-1). Cytokeratin expression was absent in all angiosarcomas. Follow-up was available for 15 cases: all patients with arteriovenous malformation and hemangioma with follow-up were disease free after complete excision; 4 cases of angiosarcoma died of the disease at 1, 1, 6, and 11 months. Our review shows that many capillary hemangiomas of the kidney are morphologically distinctive tumors, which often show "spleen-like" or "anastomosing" features. Angiosarcomas of the kidney are highly aggressive tumors with poor outcome and may have morphologic features (spindling and epithelioid change), which could result in confusion with sarcomatoid carcinomas and other renal mesenchymal tumors.