Intrasinusoidal ALK-positive anaplastic large cell lymphoma.

ALK-positive anaplastic large cell lymphoma (ALCL) may show sinusoidal involvement, but exclusive intrasinusoidal infiltration of lymph nodes is exceptionally rare. We describe a 39-year-old woman with isolated stage I inguinal lymphadenopathy, in whom the lymph node architecture was preserved despite massive intrasinusoidal infiltration by CD30- and ALK-positive atypical cells. This pattern can closely mimic metastatic carcinoma, creating a significant diagnostic challenge. Its recognition is crucial, as ALK-positive ALCL generally responds well to therapy. Further studies are required to better define the clinical and prognostic implications of this presentation.