The<unk>  nerve is a mixed cranial nerve responsible for sensory data such as tactition (pressure), thermoception (temperature), and nociception (pain) originating from the face above the jawline; it is also responsible for the motor function of the muscles of mastication, the muscles involved in chewing but not facial expression. Several theories exist to explain the possible causes of this pain syndrome. It was once believed that the nerve was compressed in the opening from the inside to the outside of the skull; but leading research indicates that it is an enlarged or lengthened blood vessel – most commonly the superior cerebellar artery – compressing or throbbing against the microvasculature of the<unk>  nerve near its connection with the pons. Such a compression can injure the nerve's protective myelin sheath and cause erratic and hyperactive functioning of the nerve. This can lead to pain attacks at the slightest stimulation of any area served by the nerve as well as hinder the nerve's ability to shut off the pain signals after the stimulation ends. This type of injury may rarely be caused by an aneurysm (an outpouching of a blood vessel); by an AVM (arteriovenous malformation); by a tumor; such as an arachnoid cyst or meningioma in the cerebellopontine angle; or by a traumatic event, such as a car accident. Short-term peripheral compression is often painless. Persistent compression results in local demyelination with no loss of axon potential continuity. Chronic nerve entrapment results in demyelination primarily, with progressive axonal degeneration subsequently. It is, "therefore widely accepted that<unk>  is associated with demyelination of axons in the Gasserian ganglion, the dorsal root, or both." It has been suggested that this compression may be related to an aberrant branch of the superior cerebellar artery that lies on the<unk>  nerve. Further causes, besides an aneurysm, multiple sclerosis or cerebellopontine angle tumor, include: a posterior fossa tumor, any other expanding lesion or even brainstem diseases from strokes.<unk>  is found in 3–4% of people with multiple sclerosis, according to data from seven studies. It has been theorized that this is due to damage to the spinal<unk>  complex.<unk>  pain has a similar presentation in patients with and without MS. Postherpetic neuralgia, which occurs after shingles, may cause similar symptoms if the<unk>  nerve is damaged. When there is no apparent structural cause, the syndrome is called idiopathic.
Trigeminal neuralgia
Postherpetic neuralgia
Occipital neuralgia
Cluster headache
Trigeminal autonomic cephalgia
Atypical trigeminal neuralgia
Thunderclap headache
Trigeminal trophic syndrome