Trigeminal neuralgia

Trigeminal neuralgia or tic douloureux corresponds to a clinical manifestation of sudden severe paroxysms of pain which usually lasts a few seconds to a few minutes, more often involving the maxillary branch of the trigeminal nerve. A vascular compression is the most prevalent cause. Other causes include compression due to CPA tumours or cysts, perineural tumour spread, or multiple sclerosis. 

Epidemiology

There is approximately an incidence of 4.3 per 100,000 / year. The vast majority of cases are unilateral, with the right side of the face being affected more commonly (1.5:1), only about 3% are bilateral. It has a peak around 60 to 70 years, with prevalence increasing with age ^1;4. The maxillary branch is the most affected and the ophthalmic branch the least.

Clinical presentation

Attacks of sudden excruciating pain, shock-like, which usually lasts a few seconds to two minutes, more often involving the maxillary branch. Typically, the pain is triggered by trivial stimuli such as talking, drinking, brushing teeth, shaving, chewing, lightly, and touching the face. However, it may also occur spontaneously ¹.

The clinical diagnoses criteria for trigeminal neuralgia are defined by the IASP (International Association for the Study of Pain) and the ICHD / IHS (International Classification of Headache Disorders / International Headache Society) as:

• paroxysmal attacks of pain lasting from a fraction of second to two minutes, affecting one or more divisions of the trigeminal nerve
• pain has at least one of the following:
  • intense, sudden, superficial or stabbing
  • precipitated by trigger factors or trigger areas
• attacks are similar among patients
• no neurological disorder is clinically evident
• not attributed to another disorder

The diagnosis of trigeminal neuralgia is based nearly entirely on the history; however some alert signs should guide a further investigation ⁴:

• difficulty in achieving pain control
• poor response to carbamazepine
• history of any skin lesions or oral lesions that could lead to a perineural spread
• associated sensory changes, deafness or other ear problems
• when affecting only the ophthalmic division or when bilateral as suggestive of benign or malignant lesions or multiple sclerosis
• patients under 40 years
• optic neuritis

Pathology

The most common cause of trigeminal neuralgia is a compressing loop of artery (most commonly the superior cerebellar artery (SCA)) or vein pressing on the trigeminal nerve at the cerebellopontine angle ², seen in ~ 95% of patients ⁴.

It has been shown that compression of the centrally myelinated, proximal or posterior segment of the cisternal portion of trigeminal nerve results in clinically significant neuralgia, not the more distal, peripherally myelinated nerve (oligodendrocyte(oligodendrocyte vs Schwann cells). The reason for this is not well understood, however. There is associated demyelination of the compressed nerve in some cases ⁶.

Although rare, posterior fossa tumours can be another cause, most commonly vestibular schwannomas, meningiomas, arachnoid cyst or epidermoid cysts ⁴.  Multiple sclerosis may also cause trigeminal neuraliga symptoms.

Radiographic features

The diagnosis of trigeminal neuralgia is based on patient's history, and an imaging study is usually indicated when there are clinical signs suggestive of this.

CT is limited in evaluating the brainstem and cisterns. MRI is the imaging modality of choice and should be considered the initial screening procedure in the assessment of patients with trigeminal neuralgia ³.

The protocol should include steady-state free precession sequence (SSFP, FIESTA etc.) and contrast.

MRI

Imaging can help diagnosing other causes such as MS and tumours. Vascular contact deforming the trigeminal nerve is seen in about 15% of cases. In such cases it is important to mention if the contacting vessel is artery or vein and if it is contacting the proximal or distal portion of the cisternal portion of the trigeminal nerve. A dedicated protocol including T2 or T1 volumetric acquisition techniques with thin slicing in all three planes should be helpful. However, an evidence-based review did not find evidence to support or refute the usefulness of MRI for this purpose ⁵.

Treatment and prognosis

The initial treatment of trigeminal neuralgia is medical, with carbamazepine and/or gabapentin.

Large surgical series have confirmed that microvascular decompression of the trigeminal nerve root is an efficient and durable treatment for trigeminal neuralgia ⁴.

Other treatment procedures include:

• gamma knife surgery (focused at the trigeminal root in the posterior fossa)
• rhizotomies (controlled lesion of the trigeminal ganglion or root by various means: thermal, chemical, or mechanical)