Rare cases of diffuse large B-cell lymphomas (DLBCL) show a prominent sinusoidal pattern where the lymphoma cells are confined to the distended sinuses of the lymph node. The image shows large monomorphic cells resembling immunoblasts filling up the sinuses. These cases are usually CD30+ and share some morphologic features with anaplastic large cell lymphomas (ALCL). However, they can be distinguished from ALCL by virtue of their B-lineage (usually express CD20 or CD79a) and lack of anaplastic lymphoma kinase-1 expression. A small subset of DLBCL with sinusoidal pattern are EBV+. The differential diagnosis of DLBCL with prominent sinusoidal pattern includes - metastatic melanoma, carcinoma, germ cell tumors, ALCL, and histiocytic lesions (Langerhans cell histiocytosis, Rosai-Dorfman disease, histiocytic sarcoma). This can usually be sorted out by doing an appropriate immunohistochemical panel of melanoma, epithelial, germ cell, and lymphoma markers. Ref: Lai R et al. Sinusoidal CD30-positive large B-cell lymphoma : a morphologic mimic of anaplastic large cell lymphoma. Mod Pathol. 2000 Mar;13(3):223-8.