Downs‐Kelly, Erinn

Rosai-Dorfman disease is a rare proliferative histiocytic disorder of lymph nodes that is descriptively known as sinus histiocytosis with massive lymphadenopathy. Extranodal involvement of the parenchyma of the breast is uncommonly reported, with fewer than 50 cases of mammary extranodal disease detailed in the English-language literature. We characterize a retrospective series of adult female patients from a single institution with Rosai-Dorfman disease of the breast and axillary lymph nodes. Because Rosai-Dorfman disease of the breast and axillary lymph nodes may clinically, radiographically, and histologically mimic breast carcinoma and other conditions, we present an illustrated review of the disease and its relevant differential diagnoses in hopes of raising awareness and allowing for accurate management of affected patients.

Mycobacterial spindle cell pseudotumor (MSP) is a rare benign spindle cell lesion containing acid-fact mycobacteria. These lesions are most commonly identified in the lymph nodes, skin, spleen, or bone marrow of immunocompromised patients and only rarely involve the lungs. We report 3 cases of pulmonary MSP, which include 2 patients who are known to be HIV-positive. The histopathological diagnosis of MSP in the lung lends itself to many challenges due to its rare incidence and its spindled tumor-like appearance. The differential diagnosis is broad and includes both benign and malignant entities. We highlight the importance of the clinical context in which these lesions typically present and the morphologic spectrum of features seen, and we offer a practical approach to the workup of pulmonary mycobacterial pseudotumor. Appropriate recognition of this entity should lead to an accurate diagnosis of a treatable benign condition despite the clinical presentation often favoring malignancy.