Anaplastic pleomorphic xanthoastrocytoma with leptomeningeal dissemination presenting with cranial neuropathy in an adult patient: illustrative case.

backgroundAnaplastic pleomorphic xanthoastrocytomas (APXAs) are rare, grade 3 malignant glial neoplasms first described as a distinct entity in the 2016 WHO classification of tumors of the CNS. They are generally seen in pediatric and young adult patients as supratentorial lesions with both solid and cystic components and have a high propensity for recurrence. APXAs occasionally demonstrate leptomeningeal dissemination (LMD) but very rarely at diagnosis. OBSERVATIONS: The authors describe the case of a 36-year-old male with a history of seizures and a known left temporal lesion since childhood, serially imaged and never biopsied, who presented with headache, increasingly frequent seizures, and right third nerve palsy. Imaging demonstrated significant interval enlargement of the lesion with intralesional hemorrhage and predominantly locoregional leptomeningeal enhancement. He underwent resection with gross-total resection achieved, and pathology revealed WHO grade 3 pleomorphic xanthoastrocytoma with ATG7::RAF1 fusion, 9p21 deletion, and telomerase reverse transcriptase promoter mutation, as identified by next-generation sequencing. This was followed by adjuvant whole-brain radiation therapy with boost and treatment with the MEK inhibitor cobimetinib. LESSONS: APXA, an already exceedingly rare primary CNS tumor, can present unusually in older adult patients with concomitant LMD and cranial neuropathy. Advanced genomic profiling can tailor adjuvant therapy. https://thejns.org/doi/10.3171/CASE24768.