Trigeminal neuralgia associated with an anomalous artery originating from the persistent primitive trigeminal artery.

A 31-year-old man presented with typical trigeminal neuralgia caused by an anomalous variant type of anterior inferior cerebellar artery (AICA) directly branching from the primitive trigeminal artery (PTA). Three-dimensional computed tomography angiography, magnetic resonance angiography, and magnetic resonance cisternography disclosed that this anomalous artery originated from the PTA and coursed to the AICA territory of the cerebellum. Microvascular decompression surgery disclosed the trigeminal nerve compressed by this AICA variant together with the superior cerebellar artery. These arteries were successfully transpositioned to decompress the nerve. Careful and thorough inspection around the trigeminal nerve verified that the PTA did not conflict with the nerve. This unusual case was caused by compression of the trigeminal nerve from the AICA directly originating from the PTA, without the more common involvement of the PTA.