[Pulmonary Castleman disease: At the crossroads of thoracic and hematologic pathology]

Castleman disease is a rare lymphoproliferative disorder listed in the latest 2022 WHOclassification under tumour-like lesions with B-cell predominance. While it primarily affects lymph nodes, rare cases of extranodal involvement have been reported. Castleman disease is divided into unicentric and multicentric forms, the latter being often associated to HHV8 infection or systemic inflammatory syndromes. Histologically, three subtypes are recognized : hyaline-vascular, plasmacytic and mixed, distinguished by morphological variations in germinal center involution, plasmacytic infiltration, follicular dendritic cell proliferation, and vascularization. Differentiating Castleman disease from lymphomas and other lymphoproliferations can be challenging, underlining the need of a diagnostic and therapeutic multidisciplinary approach. We present herein the clinical, histopathological and immunohistochemical features of a rare case of pulmonary Castleman disease, also raising questions about the classification of extranodal forms of the disease.