Isolated histiocytosis X of the pituitary stalk

A case of histiocytosis X granuloma localized in the pituitary stalk is rep orted. Coronal and sagittal magnetic resonance imaging views were useful to determine the precise size and location of the mass lesion. The diagnosis was established immunohistochemically and the patient was treated with low- dose irradiation therapy. After irradiation, the patient improved well without endocrine replacement treatment. The pituitary stalk recovered its normal size with no evidence o f recurrence on MRI at 7-year follow-up. We emphasize the importance of MRI before initiating therapy to evaluate th e pituitary mass lesion and the effective ness of low-dose irradiation for isolated histiocytosis X.