T-Cell-Rich Angiomatoid Polypoid Pseudolymphoma: A Case Report and Comparison With Key Differential Diagnoses.

T-cell-rich angiomatoid polypoid pseudolymphoma (TRAPP) is a rare and recently defined entity, conceptualized just over a decade ago. Recognition of TRAPP is important because it can be clinically and microscopically confused with low-grade cutaneous lymphomas and other vascular proliferations. We report a case of a 28-year-old male with a solitary 1.2 cm red polypoid papule on the middle posterior base of the neck. The histopathological examination revealed a well-circumscribed dermal nodular proliferation of banal-appearing lymphovascular spaces with plump endothelial cells. Immunohistochemical analysis showed a T-cell-rich infiltrate. The clinical-pathological differential diagnosis for TRAPP includes pyogenic granuloma, angiolymphoid hyperplasia (epithelioid hemangioma), acral pseudolymphomatous angiokeratoma of children, cutaneous lymphoid hyperplasia, and low-grade cutaneous lymphomas and lymphoproliferative disorders. We review the literature and discuss the key differentiating features between TRAPP and its common differential diagnoses.