Identification of BRAF V600E Mutation in Cerebrospinal Fluid Aids in Diagnosing Leptomeningeal Carcinomatosis Arising From Pleomorphic Xanthoastrocytoma: A Case Report.

backgroundPleomorphic xanthoastrocytomas (PXAs) are rare primary central nervous system (CNS) tumors that appear heterogeneous on imaging and histology and typically cause headaches or seizures on initial presentation. Alongside high rates of favorable prognosis after surgical excision exist similarly high rates of recurrence. Leptomeningeal spread on recurrence is even rarer and more challenging to diagnose. CASE: We describe a case of a 40-year-old man with a history of surgically resected PXA presenting 12 years later with persistent headaches and lower back pain. Imaging studies revealed arachnoiditis, and a subsequent brain biopsy was nondiagnostic. Serial CSF studies only revealed the presence of atypical cells too few to further characterize via standard histology studies, with rare small lymphocytes and monocytoid cells. Submitting these cells for next-generation sequencing ultimately revealed a BRAF V600E mutation typically found in PXAs, thereby confirming the diagnosis of leptomeningeal recurrence and revealing a therapeutic target.

conclusionThis case highlights the utility of next-generation sequencing as a means of non-invasively diagnosing leptomeningeal disease in recurrent PXA and potentially in other cancer types as well.