[An atypical form of neurosarcoidosis]. / Neurosarcoïdose de présentation atypique.

INTRODUCTION: Nervous system involvement occurs in 5 to 15% of the patients with sarcoidosis. Neurosarcoidosis remains very difficult to diagnose because clinical presentation and imaging characteristics lack specificity. OBSERVATION: We report a 26-year-old man who gradually developed headaches, memory disturbance and epilepsy. CT-scan and MRI showed a temporal-parietal cystic mass, secondary to a rare and focal form of hydrocephalus, called "trapped temporal horn" revealing neurosarcoidosis. CONCLUSION: The "entrapped temporal horn" is due to an obstacle on the cerebrospinal fluid pathway at the trigone of the lateral ventricle that seals off the temporal horn and the choroid plexus from the rest of the ventricular system. The obstacle is related to the granulomatous tissue of sarcoidosis. Therefore, the "trapped temporal horn" acts as a space occupying process, causing headaches, memory pain, hemiparesis, homonymous hemianopsia, and requires medico-surgical management.