Sinus histiocytosis with massive lymphadenopathy. Multiple skull involvements.

Sinus histiocytosis with massive lymphadenopathy is a non-neoplastic self-limiting disease of the bone marrow stem cell origin. It is characterized by painless, bilateral cervical lymphadenopathy accompanied by fever, leukocytosis, elevated erythrocyte sedimentation rate and hypergammaglobulinemia. Extranodal involvement including bone is rare. The patient is a 45-year -old female with multiple punch out lesions on her skull. MRI findings included iso-signal intensity mass at the diploid space on T1 weighted image and on T2 weighted image, mild high signal intensity was obtained. Histologically, the lesion showed proliferation of histiocytes in the fibroblastic background with formation of reactive germinal centers and many plasma cells. The histiocytes show round nuclei and occasional nucleoli and abundant cytoplasms. In area, there is lymphocytophagocytosis. Immunohistochemically, the histiocytes were positive for S-100 protein and lysozyme.