Résumé
Chondroid chordoma commonly presents as clival osseous and extradural mass. A 15-year-old boy presented with progressive visual deficit, headaches and diplopia since three years. Computed tomography (CT scan) showed a skull base tumour, but was wrongly reported at the time as chronic sphenoidal sinusitis and nasal polyps. In the past three months, he developed dysphagia, urinary retention and constipation. Terminally, he had weakness of all limbs. Fundoscopy showed optic atrophy. Temporal and spatial variation in symptoms led to a clinical diagnosis of multiple sclerosis with optic neuritis. Partial brain autopsy revealed small gelatinous tumour nodules in the subarachnoid space of middle cranial fossa encasing base of brain like arachnoiditis. Tumour deposits extended down into the spinal cord along the subarachnoid space as far as vision allowed. Histopathology and immunohistochemistry confirmed a diagnosis of chondroid chordoma. Awareness of this rare mode of dissemination will avoid misdiagnosis and delay in treatment.