Herpes trigeminal neuritis and rhombencephalitis on Gd-DTPA-enhanced MR imaging.

Trigeminal neuritis usually is caused by an inflammatory reaction to herpes simplex virus, which often resides within the gasserian ganglion of the trigeminal nerve. Transaxonal movement of the virus between the ganglion and peripheral nerves within the oral cavity has been documented [1 , 2]. The virus can be isolated from the painful aphthous ulcers within the oral cavity and the typical cold sore lesion often seen at the border of the lips. Herpes simplex virus type 1 occasionally involves the brain by retrograde spread from the gasserian ganglion along the preganglionic segment of the fifth nerve to the brainstem. This has been referred to as rhombencephalitis [3 , 4]. We describe the MR findings in a patient with brainstem encephalitis and the typical clinical features of herpes simplex trigeminal neuritis in whom enhancing trigeminal nerve lesions returned to normal appearance 6 weeks after initial study without any form of treatment.