Hypocellular anaplastic large cell lymphoma mimicking inflammatory lesions of lymph nodes.

The subgroup of T/null-cell primary systemic anaplastic large cell lymphoma that expresses anaplastic lymphoma kinase (ALK) constitutes a distinctive clinicopathologic entity that exhibits a broad morphologic spectrum. The examples predominated by small cells or showing a mixed cell population can be difficult to recognize as being neoplastic. We report four such cases with a remarkably hypocellular granulation tissue-like appearance, mimicking an inflammatory or reparative process. All patients were young and presented with lymphadenopathy in multiple sites. The lymph node biopsies showed a hypocellular appearance, with wide separation of the small to medium-sized lymphoid cells by edematous or fibromyxoid stroma. There were interspersed spindly neoplastic cells resembling myofibroblasts, sometimes forming short, sweeping fascicles, as well as histiocytes. Occasional large cells with atypical nuclei were identified. The larger lymphoid cells tended to form cuffs around the venules. In two cases, the capsule and fibrous trabeculae were markedly broadened with increased spindly cells, mimicking inflammatory pseudotumor of lymph node. Immunostaining showed dispersed and clustered CD30+ ALK+ cells, confirming a diagnosis of anaplastic large cell lymphoma. In conclusion, a diagnosis of hypocellular anaplastic large cell lymphoma requires a high index of suspicion. The young age of the patients and the presence of perivascular cuffs of larger lymphoid cells should provide the strongest clues to the correct diagnosis.