The Anatomy of the Geniculate Ganglion

The geniculate ganglion is a collection of sensory neurons of the facial nerve, which is the seventh cranial nerve (CN VII). The ganglion is located in a bony structure that's called the facial canal. It receives fibers from several components of the facial nerve, then sends out fibers to multiple muscles, glands, the tongue, and other structures. It’s involved in taste, the secretion of tears and saliva, facial expression, and several other functions.

Anatomy

A nerve ganglion is a group of nerves enclosed by a capsule of connective tissue. Typically, all of the nerves in a ganglion will have similar or related functions. It may help to think of a ganglion as a relay station or intermediary connection between different structures of the nervous system. The plural of “ganglion” is “ganglia.”

You have 12 cranial nerve ganglia on each side of your brain. As with nerves, they’re generally referred to in the singular even though they exist in generally symmetrical pairs.

Cranial nerves originate in the back of your head and travel forward toward your face, supplying nerve function as they go. Some deal with motor function (movement), some deal with sensory information (touch, taste, smell, vision, hearing, temperature), and some deal with both. Those are called mixed nerves.

Four of your cranial nerve ganglia are parasympathetic and eight are sensory. The geniculate ganglion is one of the sensory ganglia, meaning that it helps gather information from your senses and transmit it to and from your brain. It's also connected to secretomotor fibers, which are the ones that help the glands to secrete their fluids.

Structure and Location

The geniculate ganglion is part of the facial nerve, which is one of the longest cranial nerves and has a complex anatomy. It has two roots that arise from the brainstem (the structure that connects the brain and spinal cord) in the back of your head. One root is motor and the other is sensory. Inside your skull, the two roots travel forward and pass near the inner ear. There, they enter a Z-shaped structure called the facial canal.

In the facial canal, the two roots fuse together. At the first bend of the Z, they form the geniculate ganglion.

The ganglion then sends out nerve fibers to several nerve branches, including:

• Tympanic (ear) segment of the facial nerve
• Greater superficial petrosal nerve
• Lesser petrosal nerve
• External petrosal nerve

Fibers from the geniculate ganglion also innervate (provide nerve function to):

• Glands: Lacrimal (tear), submandibular and sublingual (salivary)
• Muscles: Posterior belly of the diagastric (deals with anchoring structure of the tongue), stylohyoid (lifts the tongue), numerous muscles involving facial expression
• Other structures: Tongue, palate (roof of the mouth), pharynx (throat-area immediately behind the nose and mouth), external auditory meatus (ear canal)

The ganglion itself is pyramid-shaped and between 1 and 2 millimeters long.

Anatomical Variations

Discussions of anatomy generally focus on what’s typical, but not everyone's anatomy is exactly the same. Variations in nerve structures and routes exist, and they're important for doctors to know when it comes to diagnosis and treatment—especially when that treatment is surgery.

Studies have revealed a few abnormalities that involve the geniculate ganglion:

• In between 10% and 20% of people, the bone that forms the facial canal isn’t fully closed, which leaves the ganglion and some of its surrounding nerve structures exposed during surgery to the area around the ganglion, and therefore vulnerable to injury.
• The angle of the facial canal that contains the geniculate ganglion varies significantly from person to person, ranging from 19 degrees to 107 degrees.
• The distance from the geniculate ganglion to an opening in the canal called the hiatus fallopi can vary by up to 7.75 millimeters.

The size and shape of the ganglion itself are fairly consistent.

All of this information can help a surgeon determine the best approach to take during a procedure to minimize the risk of accidentally damaging the ganglion as well as the nerves and other structures around it.

Function

The geniculate ganglion contains special sensory cells for your sense of taste that receive information from:

• The front two-thirds of your tongue via the chorda tympani nerve
• Two areas of the palate via the greater petrosal nerve

In addition, it gets sensory input from the sensory branch of the facial nerve, which is sometimes called the intermediate nerve or nervus intermedius. This information comes from:

• The skin in a small area behind the ear
• The outer surface of the tympanic membrane (eardrum)

After these sensory signals come into the ganglion, it then relays them to the appropriate structures in the brainstem for processing.

Associated Conditions

The geniculate ganglion can be damaged by trauma or disease. Several medical conditions are associated with it, determined by the exact location and the nature of the damage.

Problems with the geniculate ganglion are associated with several forms of facial paralysis:

• Ramsay Hunt syndrome
• Bell’s palsy
• Geniculate ganglion schwannoma

Ramsay Hunt Syndrome

Herpes zoster oticus, which is the virus that causes chickenpox, can reactivate later in life as a highly painful condition called shingles. When shingles strikes near the geniculate ganglion, it causes Ramsay Hunt syndrome. This typically happens only on one side of the face at a time.

Primary symptoms of Ramsay Hunt syndrome, which occur only on the affected side, can include any combination of:

• Hearing loss
• A red, painful rash characterized by blisters around the ear or mouth
• Facial weakness or paralysis that may cause drooping of the eyelid and side of the mouth

Other symptoms may include:

• Ear pain
• Difficulty closing the eye on the affected side
• Dry mouth and eyes
• Changes in or loss of your sense of taste
• Nystagmus (jittery unintentional eye movements)
• Tinnitus (ringing of the ears)
• Vertigo (sensation of spinning)
• Nausea and vomiting

Early treatment is crucial for preventing long-term complications, so be sure to get medical help right away if you experience these symptoms.

Possible complications are:

• Permanent hearing loss
• Permanent facial weakness and drooping
• Damage to the eye that causes pain and blurry vision
• Postherpetic neuralgia (lingering nerve pain)

Treatment often involves antiviral medications and corticosteroids. Depending on your specific symptoms, the doctor may also prescribe standard pain medications (analgesics), anti-seizure drugs to help with nerve pain, and medications for vertigo. When the eye is involved, artificial tears and/or other lubricating products may be used to prevent damage to the cornea.

Vaccines for chickenpox and shingles are the best defense against Ramsay Hunt syndrome.

Bell’s Palsy

Bell’s palsy and Ramsay Hunt syndrome are often indistinguishable based on symptoms alone; the suspected causes and treatments, however, are different.

Bell’s palsy is due to inflammation of unknown origin involving the geniculate ganglion. That can compress the facial nerve inside the fallopian canal.

Symptoms of Bell’s palsy can vary. They occur only on one side of the face and may include:

• Weakness, from mild to total paralysis
• Twitching
• Drooping eyelid and corner of the mouth
• Drooling
• Dry eye or excessive tearing
• Dry mouth
• Impaired sense of taste
• Pain around the jaw and behind the ear
• Tinnitus
• Headache
• Hypersensitivity to sound
• Impaired speech
• Dizziness

Bell's Palsy usually takes 3 - 6 months to resolve with or without treatment. When treatment is necessary, it typically involves corticosteroids to reduce inflammation, antivirals in case of herpes infection, and common painkillers. The eye should be kept lubricated with drops or other lubricating products, and an eye patch is often recommended. Plastic surgery may be performed to correct facial deformities such as a crooked smile or an eyelid that won’t close properly.

Geniculate Ganglion Schwannoma

This ganglion may develop a rare tumor called a geniculate ganglion schwannoma. Schwannomas are tumors involving Schwann cells, which help conduct impulses in the cranial nerves and the peripheral nervous system.

Symptoms include:

• Facial paralysis
• Impaired flow of tears
• Hearing loss

Some cases of geniculate ganglion schwannoma don’t require treatment. In those that do, microsurgery may be done to repair the facial nerve. A procedure called stereotactic radiosurgery, a kind of radiation therapy used on small brain tumors, may also be recommended.