Benign vascular proliferation of lymph nodes with characteristic sinus distribution.

Vascular transformation of sinuses (VTS) is a rare condition in which the vasoproliferative process is restricted to the lymph node sinuses and does not involve the parenchyma, capsule, or perinodal fibroadipose tissues (1,2,3,4,5). In the original description, the cause of VTS was believed to be thrombosis of the perinodal veins, which had been identified in all three cases (1). In experiments in rabbits, VTS was reproduced by occluding efferent lymphatics and veins (6). Lymphatic or venous obstructions, sometimes at more distal sites, caused by a variety of conditions—tumors (4,7,8,9,10), congestive heart failure (11,12), thrombosis of major vessels (12), surgical procedures, and radiotherapy (13)—were identified in other reports, as well as in a survey of 76 cases (5). Despite this frequent association, vascular obstruction alone may not explain the exuberant proliferation of vessels within the lymph node sinuses, which occurred in some cases in lymph nodes draining cancer or hemangioma without vascular occlusion (14) and even in association with cirrhosis (15) and myelodysplasia (16). It has been suggested that angiogenetic factors released by activated lymphoid cells under conditions not fully understood may induce the proliferation of blood vessels in the lymph node sinuses (5,14). Other types of benign vascular proliferation in lymph nodes have been described under the names of nodal angiomatosis (17,18), nodular spindle cell vascular transformation of lymph nodes as a variant of VTS (8), hemangiomatoid lesion (19), angiomyomatous hamartoma (9), and in association with infectious processes such as toxoplasmosis (20), human immunodeficiency virus infection (21,22), and bacillary angiomatosis (23). Some of these entities are poorly defined, and differentiating between them and Kaposi sarcoma (KS) remains difficult because of overlapping histologic patterns and poorly understood mechanisms of vascular proliferation.