Medulloblastoma with leptomeningeal metastases.

A 27-month-old previously healthy boy was brought to the hospital presenting with signs of raised intracranial pressure including vomiting, irritability, adducted right eye, and fever. Urgent magnetic resonance imaging (MRI) of the brain showed a small T1and T2-weighted isointense nodule (Fig 1), which enhanced avidly over the right lateral aspect of the fourth ventricle after intravenous contrast (Fig 2). Features on diffusion-weighted image (DWI) of bright signal intensity and apparent diffusion coefficient (ADC) map of low values (0.67-0.78 x 103 mm2/s) in the abnormal area suggested restricted diffusion of the nodule at the fourth ventricle (Fig 3). In addition, diffuse nodular supratentorial and infratentorial leptomeningeal enhancement was noted (Fig 4). Considering the age of the patient, and the location and characteristic imaging features of the lesion, a diagnosis of medulloblastoma with leptomeningeal metastases was proposed by the radiologists. The diagnosis was later confirmed by excisional biopsy.