Erdheim-Chester Disease Mimicking a Malignant Pituitary Stalk Tumor With Ventricular Dissemination: A Case Report.

Erdheim-Chester disease (ECD) is a rare form of non-Langerhans cell histiocytosis characterized by multi-organ involvement, most commonly affecting the long bones, retroperitoneum, heart, lungs, skin, and central nervous system (CNS). Approximately half of reported cases exhibit CNS involvement, which may affect both intra- and extra-axial compartments. On MRI, ECD typically presents as a strongly enhancing mass lesion, often mimicking neoplastic or infectious conditions. With advances in genetic understanding, ECD is now recognized as a hematologic malignancy of histiocytic origin, driven by mutations in key components of the MAPK signaling pathway. Among these, the BRAF mutation is the most frequently observed genetic alteration and often provides a valuable clue for differential diagnosis. However, in cases lacking typical clinical features and the absence of BRAF mutation, diagnosis becomes significantly more challenging. We report the case of a 32-year-old man who presented with a pituitary stalk mass and ventricular dissemination, ultimately diagnosed with BRAF wild-type ECD harboring a CSF1R mutation, which has recently been implicated as a potential driver within the MAPK pathway. A deeper understanding of the molecular pathogenesis of ECD may not only aid in accurate diagnosis but also contribute to improved clinical outcomes.