Objective and importance: Sinus histiocytosis or Rosai-Dorfman disease (RDD) is a rare but well-recognized disorder characterized by an unusual proliferation of histiocytic cells. Intracranial localization is a rare manifestation of RDD. Only three cases of localization in the posterior fossa have been reported in the literature. The present report describes the first case, to our knowledge, of cerebellar localization of RDD.
Clinical presentation: A 67-year-old woman was admitted to our institution with a 5-month history of cerebellar ataxia. Her medical history was unremarkable. The patient was alert and cooperative. No cranial nerve deficits were evident; Romberg positivity to the left side was recorded. No cutaneous abnormalities, lymphadenopathy, or hepatosplenomegaly were revealed by physical examination. Routine hematological and biochemical studies were normal except for the erythrocyte sedimentation rate, which was elevated. Radiologically, the lesion appeared as a well-defined and avascular mass in the right cerebellar lobe. Meningioma was considered the most likely diagnosis.
Technique: The patient underwent a suboccipital craniotomy with complete excision of the lesion. Microscopic examination of the operative specimen revealed the presence of a mixed cellular population with predominant mature histiocytes. A peculiar feature was the presence of lymphocytes and monocytes within the cytoplasm of histiocytes (emperipolesis). Immunohistochemical study of the histiocytes revealed strong positivity for S-100, CD-68 antigen, and vimentin.
Conclusion: Involvement of the central nervous system in RDD appears to have a benign prognosis, especially in the absence of nodal diseases. Surgery is essential for diagnosis, and, when total removal is achieved, the outcome is generally good without risk of recurrence.