Teaching NeuroImages: CNS pituitary-hypothalamic Langerhans cell histiocytosis in an adult

A 66-year-old man presented with a 6-month history of worsening confusion and panhypopituitarism. MRI showed a 1.7-cm enhancing mass involving the infundibulum and hypothalamus.1 Total body PET scan showed isolated uptake in the hypothalamus (standardized uptake value 25.3) (figure 1). Full body CT, lumbar puncture, and infectious workup were negative. Endoscopic transventricular biopsies were performed. Microscopy revealed gliotic hypothalamus with clusters of cells with elongated grooved nuclei positive for CD1a, Langerin, BRAF ( V600E ), CD68, CD163, and S-100 by immunohistochemistry and negative for Grocott methenamine silver, Gram stain, acid-fast bacilli, Warthin-Starry, herpes simplex virus 1 and 2, Epstein-Barr virus, and β-amyloid, confirming the diagnosis of Langerhans cell histiocytosis (figure 2). The finding of BRAF (V600E) positivity is important diagnostically and as a potential therapeutic target.2