The Anatomy of the Trigeminal Ganglion

The trigeminal ganglion is also called the Gasserian ganglion, semilunar ganglion, or Gasser's ganglion. It is part of the trigeminal nerve, which gathers sensory stimuli from the head and face and provides nerve stimulation to the muscles that control chewing. (A nerve ganglion is a group of nerves that typically function similarly to each other and are enclosed by connective tissue.)

The trigeminal ganglion can be affected by a number of medical conditions, the most common of which are shingles and trigeminal neuralgia. This ganglion can be damaged by trauma, tumors, or infections.

Structure

The three sensory branches of the trigeminal nerve—the ophthalmic nerve, the maxillary nerve, and the mandibular nerve—converge at the trigeminal ganglion before the trigeminal nerve continues on to enter into the brainstem. The brainstem is physically the lowest part of the brain, located at the back of the head, right above the spine.

Anatomy

The trigeminal ganglion is about 2 millimeters in size and rounded in shape. It is the largest of the cranial nerve ganglia and it is the widest part of the trigeminal nerve.

Location

The trigeminal ganglion lies in a space near the top of the temporal bone, on the inside of the skull, anterior to (in front of) the ear. The ganglion is enclosed and covered by Meckel’s cave, which is also called the trigeminal cistern. As the name implies, it is cavelike in shape.

Meckel’s cave is a structure made of dura matter, which is part of the meningeal covering (the protective lining that surrounds the brain and spine). Cerebrospinal fluid (CSF) surrounds the trigeminal ganglion, providing nourishment.

The trigeminal ganglion is located close to the pons of the brainstem. The brainstem is composed of three sections—the pons is the middle section and it is below the midbrain and above the medulla (which is continuous with the spine). The nerve fibers of the trigeminal nerve enter the brainstem at the level of the pons, which contains the root and nerve fibers of the trigeminal nerve that travel up to higher regions of the brain.

Anatomic Variations

The trigeminal ganglion itself may be affected by abnormalities in nearby structures, such as an aneurysm (outpouching) of the internal carotid artery. An aneurysm can compress the nerve, causing symptoms of dysfunction, including pain, sensory loss, tingling, or weakness of the muscles that control chewing.

Function

The trigeminal ganglion has sensory and motor functions.

It receives sensory input from the three sensory branches of the trigeminal nerve. These branches bring sensation from the face and head to the ipsilateral trigeminal ganglion, which sends the sensory messages into the brainstem. That sensory information is transmitted from the brainstem and crosses over to the other side of the brain, eventually reaching the thalamus and then the sensory strip of the cerebral cortex on the opposite side of the brain.

The motor branch of the trigeminal nerve receives its messages from the motor region of the cerebral cortex. These messages cross over in the brainstem and pass through the trigeminal ganglion and eventually to the muscles that control chewing.

Motor Function

The motor branch of the trigeminal nerve controls several muscles, including the temporalis, masseter, the medial and lateral pterygoids, the mylohyoid, the tensor tympani, the tensor vali palatini, and the anterior belly of the digastric muscle.

Sensory Function

The three sensory branches of the trigeminal nerve bring in sensation to the trigeminal ganglion from the forehead, scalp, eyelids, eyes, cheeks, mouth, lips, gums, the roof of the mouth, teeth, tongue and outer part of the ear. This allows the body to detect light touch, pain, temperature, and position of these areas of the face and head.

Associated Conditions

Shingles and trigeminal neuralgia are painful conditions associated with the trigeminal ganglion. Other conditions affecting this ganglion are not as common as conditions affecting the trigeminal nerve because the ganglion is relatively small and is less likely to be injured. Nevertheless, there are several medical conditions associated with trigeminal ganglion.

Shingles

Shingles is a painful condition that occurs due to the reactivation of the herpes zoster virus, which causes chickenpox. If you have had a chickenpox infection at some time in your life, the virus can remain in the body in an inactive state for many years.

The inactive virus is located in a ganglion, and it can lie in any ganglion throughout the whole body, including the trigeminal ganglion. The virus can reactivate later in life, particularly if your immune system becomes weak. Reactivation is very common.

Symptoms include pain and fluid-filled lesions in the region of the sensory nerve. If the virus has remained in the trigeminal ganglion, then reactivation causes severe pain one side of the face and eye and a rash. Some people also develop redness or bumps around or in the eye, requiring medical attention. Shingles typically resolves after a few weeks. Anti-viral medications, started within 72 hours of the rash appearance, can decrease the duration and severity of the pain.

Post-Herpetic Neuralgia

A rare complication of shingles, post-herpetic neuralgia occurs when a person has prolonged pain after an episode of shingles.

Trigeminal Neuralgia

A condition characterized by pain on one side of the face, trigeminal neuralgia can involve one or more branches of the trigeminal nerve. The symptoms of this condition may improve with medication, but sometimes the pain is persistent and does not improve with medical treatment.

A procedure called a Gasserian block involves injecting an anesthetic and/or anti-inflammatory medication into the trigeminal ganglion to relieve the pain of trigeminal neuralgia. The effects of the procedure may last for weeks or months, and may also cause a side effect of decreased sensation in the head and face. Often, the condition resolves after a Gasserian block, but sometimes it is persistent and the procedure may need to be repeated.

Cancer, Trauma, or Infection

Any condition that damages the trigeminal ganglion can cause pain, and sometimes weakness. A traumatic injury, a brain tumor, metastatic spread of cancer, or infection can reach the trigeminal ganglion, triggering symptoms.

Trophic Syndrome

A rare disorder that can be caused by a number of different things including trauma, stroke, infection and surgery, trophic syndrome is characterized by pain and ulcerations of one or more of the three branches of the trigeminal nerve. This condition is treated with pain medications and skincare.

Rehabilitation

A relatively new treatment approach for the treatment of trigeminal pain involves neurostimulation of the trigeminal ganglion using implantable electrodes. This method is off-label as it has only been studied in small groups of participants, but the results are promising.