A singular case of intracranial sinus histiocytosis without massive lymphadenopathy: Isolated Rosai-Dorfman disease of the hypothalamus

Background Sinus histiocytosis with massive lymphadenopathy (also known as Rosai-Dorfman disease [RDD]) is a benign but chronic cervical lymphadenopathy associated with systemic inflammation. Although extranodal manifestations of RDD have been described, isolated central nervous system (CNS) involvement is exceedingly rare. Case Description We present the case of a 66-year-old woman who presented with 3 weeks of intermittent headaches, diplopia, and increasing confusion who was found on work-up to have isolated hypothalamic RDD, evidenced by a dense admixture of large histiocytic cells admixed with numerous small mature lymphocytes and some scattered plasma cells and neutrophils on stereotactic brain biopsy. Over 19 months of follow-up, neurologic examination continues to reveal stable bilateral partial abducens nerve palsies without diplopia, and a new gradual onset short-term memory loss. Interim treatment for the histiocytic lesion consisted of 10 cycles of external-beam radiation therapy along with high-dose steroids. The patient currently experiences minimal functional loss from treatment of her intracranial sinus histiocytosis, with a Karnofsky performance status of 80, and she remains without any disease involvement outside of the CNS. Conclusion Because misdiagnosis of a hypothalamic contrast-enhancing lesion could potentially lead to therapeutic mismanagement and poor outcomes, it is important to consider RDD in the differential diagnosis.