Medulloblastomas are the most common brain tumors among children. The incidence of medulloblastoma decreases with age and is rare in the adult population. We present a unique case of disseminated primary leptomeningeal medulloblastoma with no primary brain mass.

Case Description

A 24-year-old female with past medical history of anxiety presented to the hospital due to a one-week history of headaches and 3-months of lower extremity weakness. Neurological exam showed decreased strength and sensation in bilateral lower extremities as well as decreased left patellar and bilateral ankle reflexes. She also had antalgic gait. Her mental status, cranial nerves, and coordination exam were normal. MRI brain and spine showed extensive leptomeningeal disease. Lumbar spine thecal sac biopsy showed clusters of small round blue cells. Immunostaining of the associated cytology specimen was positive for chromogranin and synaptophysin and negative for pan-CK and CD30. RNA profiling fit a pattern of medulloblastoma with positive YAP1 stain, but negative GAD. No primary tumor mass was found.

Primary leptomeningeal medulloblastoma is a rare presentation in the pediatric population and there have been fewer cases published in literature of this in the adult population. Diagnosis of primary leptomeningeal medulloblastoma is challenging due to insufficient sampling with CSF cytology and the proficiency required for thecal biopsy. Even with sufficient tissue for histopathology, the “small, round, blue cells” seen in medulloblastomas have to be differentiated from other adult cancers such as meningeal metastases from small cell lung cancer. Surgical resection of the primary tumor has shown to increase survival rates in children; however, this is not possible with primary leptomeningeal disease. A combined modality of craniospinal irradiation and chemotherapy can be considered, although chemotherapy regimens in this disease are usually associated with many side effects in adults and are not well-tolerated due to the intensity of regimens.