MR imaging of middle cranial fossa arachnoid cysts: temporal lobe agenesis syndrome revisited.

MR studies in eight patients with extraaxial arachnoid cysts in the middle cranial fossa were reviewed in order to identify any associated structural defect in the ipsilateral temporal lobe. The study was prompted by the original theory that agenesis of the temporal lobe is the primary factor in the development of these cysts. Authors of subsequent studies proposed that the cysts are a consequence of embryological malformation of the meninges only and that the adjacent temporal lobe is compressed. Our findings suggest that middle cranial fossa cysts are associated with temporal lobe hypogenesis, and also that compression of the temporal lobe is an infrequent accompaniment.