Trigeminal Nerve Block

Trigeminal nerve block provides hemifacial anesthesia and is used predominantly in the diagnosis and treatment of neuralgia. It is a relatively underused procedure, mainly owing to the difficulty of achieving a reliable block. Before proceeding with the block, one should have a precise knowledge of the anatomy, should be thoroughly familiar with the details of the procedure, and should be fully aware of the potential complications.

Trigeminal nerve block is indicated for the following ^{[1, 2]} :

• Treatment of trigeminal neuralgia

• Diagnostic testing

• Recalcitrant herpes zoster ophthalmicus

• Postherpetic neuralgia

Trigeminal neuralgia is characterized by spontaneous, paroxysmal lancinating pain in the trigeminal nerve distribution. Often, the cause is not known. Occasionally, tumor infiltration, vascular compression of the nerve, or diseases such as multiple sclerosis may be the causative factors. Therefore, these patients should undergo complete neurologic evaluation.

Oral carbamazepine is the drug of choice and is effective in the majority of cases; trigeminal nerve block is reserved for patients who do not respond to medical treatment or patients in whom neurologic decompression of the canal is not feasible or has failed. ^{[3, 4]}

Before neurolysis is carried out, the patient’s response to a diagnostic block with local anesthetic must be assessed.

Trigeminal nerve block is contraindicated for the following:

• Patients who refuse the procedure

• Patients who have coagulation abnormalities or are taking anticoagulant drugs

• Patients on antiplatelet medications

• Pregnant women

The trigeminal nerve is the fifth cranial nerve and supplies sensory innervations to the face via its branches (see the image below). The trigeminal nerve ganglion (also referred to as the gasserian ganglion) lies in the trigeminal cave (also known as the Meckel cave), which is a dural invagination in the petrous part of the temporal bone. This ganglion is formed by 2 roots that exit the ventral surface of the brainstem at the midpontine level and travel forwards and laterally to enter the trigeminal cave.

Sensory distribution of the trigeminal nerve

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The trigeminal ganglion is bounded medially by the cavernous sinus, superiorly by the inferior surface of the temporal lobe, posteriorly by the brainstem, and anteriorly by its exiting 3 branches (ophthalmic, maxillary, and mandibular; see the image below). The dural pouch (trigeminal cistern) contains cerebrospinal fluid (CSF) and lies behind the ganglion. The postganglionic fibers are the sensory nerves to the face and exit via various foramina at the base of the skull.

Trigeminal ganglion and its major branches

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The structures supplied by the branches of the trigeminal ganglion are as follows (see the image above):

• Ophthalmic branch (V1) – This provides the sensory supply to the eyes and forehead; it exits at the superior orbital fissure, and its branches are the nasociliary, lacrimal, and frontal nerves

• Maxillary branch (V2) – This supplies the midface and upper jaw; it exits via the foramen rotundum, and its branches include the zygomatic, infraorbital, superior alveolar, and sphenopalatine nerves

• Mandibular branch (V3) – This supplies the lower jaw; it exits via the foramen ovale, and its branches are the lingual, auriculotemporal, inferior alveolar, buccal, and mental nerves

The ophthalmic and maxillary nerves are purely sensory. The mandibular nerve has sensory and motor functions. For more information about the relevant anatomy, see Trigeminal Nerve Anatomy.

The success of a trigeminal nerve block depends on proper identification of the anatomic landmarks and the nerve itself. The duration of the block depends on the agent used. Local anesthetics typically provide analgesia lasting up to 12 hours, whereas neurolytic agents such as glycerol or alcohol have effects lasting for up to 6 months. Radiofrequency ablation has a 98% success rate and yields a longer pain-free period. Treatment with glycerol has a success rate of 70-90% and a recurrence rate of 54% at 4-year follow-up.

In a study of 79 patients who underwent either percutaneous anhydrous glycerol rhizolysis (PRGR) or radiofrequency (RF) thermocoagulation, 23 (58.9%) of the 40 PRGR patients and 33 (84.6%) of the 39 RF patients experienced excellent pain relief. The mean duration of excellent pain relief in the 2 groups was comparable. ^[5] By the end of the study period, 39.1% of the PRGR patients and 51.5% of the RF patients had experienced recurrence of pain.