To report a rare case of IDH-mutant adult brainstem glioma in a young adult woman with diffuse leptomeningeal involvement.

Adult brainstem glioma is a rare clinical entity constituting less than 2% of adult brain tumors, and is  poorly understood compared to adult supratentorial glioma and pediatric brainstem glioma. Symptoms at presentation are often nonspecific, the radiologic appearance is variable, and location-specific obstacles to biopsy present diagnostic challenges. 

Single institution retrospective case report.

A 34-year-old woman with no known history of malignancy presented with three months of occipital headaches and one month of amnestic spells characterized by psychomotor agitation.  Neurologic examination was remarkable for right eye relative afferent pupillary defect, optic disc edema, lateral gaze palsy, bilateral ptosis, hearing loss, and notably intact peripheral strength, sensation, and reflexes.  Lumbar puncture indicated a high opening pressure (350mmHg), neutrophilic pleocytosis (WBC 367), and markedly elevated protein (>1000).  MRI Brain revealed an expansile non-enhancing T2 hyperintense medullary lesion with pontine extension (2.5cm x 1.5cm), leptomeningeal enhancement in Meckel's cave, cerebellum, and interpeduncular cistern, with sylvian atrophy and signs of transependymal flow.  Spinal MRI showed robust contrast-enhancing leptomeningeal disease encasing the cord and roots, prompting L3/L4 laminectomy for intradural biopsy.  Molecular testing revealed mutations in IDH1 (p.R132G), NRAS (p.Q61K), and TP53 (p.R273C), with NF2 copy number loss leading to a final integrated diagnosis of anaplastic astrocytoma, IDH-mutant, WHO Grade III.

Diffuse midline gliomas typically harbor histone H3 alterations that confer a uniformly poor prognosis regardless of histologic features.  Here, the molecular profile (IDH1, TP53) is more typical of hemispheric astrocytomas, has only rarely been reported in the brainstem, and additionally demonstrates the uncommon finding of leptomeningeal dissemination at time of diagnosis.