Primary brain stem tethering: a rare cause of geniculate neuralgia.

This rare case of brain stem tethering presented with chronic and progressive geniculate neuralgia. In view of the fact that an occipital subcutaneous lipoma had been resected in childhood, it probably concerned a primary tethering, fitting in with an occult occipital dysraphism. Magnetic resonance imaging (MRI) clearly demonstrated an underlying tethering, causing a distortion of the brain stem. Consequently, this led to the hypothesis that the geniculate neuralgia could be explained by traction on the lower cranial nerves secondary to the brain stem displacement. Untethering resulted in a considerable decrease of the neuralgia. MRI proved to be essential in the diagnosis and treatment of this unusual case.