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The glossopharyngeal nerve is also called the ninth cranial nerve. Cranial nerves are vital nerves that arise from the brain that help the brain control muscles, process the five senses, and control glands in the body. As its name implies, the glossopharyngeal nerve originates in the brain near the base of the skull, exits the skull through a large hole called the jugular foramen, and terminates in the back of the mouth and throat. The glossopharyngeal nerve allows perception of taste on the hindmost portion of the tongue, delivers the sensations of pain and touch from the throat and tongue, and exerts control over the muscles used during swallowing.
It is difficult to evaluate the glossopharyngeal nerve alone, but physicians typically examine the gag reflex and taste on the posterior tongue to determine glossopharyngeal function. Isolated ninth nerve lesions are extremely rare. Tumors at the junction between the cerebellum and pons in the brain stem can damage the eighth nerve, which mediates balance and hearing, as well as the ninth nerve. Masses near the jugular foramen can compress the ninth, tenth, and eleventh nerves. Diphtheria can cause ninth nerve paralysis. Bouts of unconsciousness associated with swallowing, called swallow syncope, are rare complications of ninth and tenth nerve lesions.
Glossopharyngeal nerve abnormalities cause difficulty in swallowing. Affected patients will notice impaired taste of the posterior one-third of the tongue and palate. There may be reduced sensation to touch or pain over the posterior tongue, palate, and throat. The gag reflex is absent in these cases. Dysfunction of the parotid gland leads to decreased saliva production and dry mouth.
With bouts lasting from seconds to minutes, glossopharyngeal neuralgia is a condition in which recurring attacks of excruciating pain occur in the ear, throat, tonsils, and tongue. The cause of the neuralgia is irritation of the glossopharyngeal nerve due to pressure from nearby blood vessels, tumors, growths, or infections in the skull base, mouth, or throat. Triggering activities for the bouts of pain include swallowing, speaking, laughing, coughing, or chewing. Slow heart beat and fainting have occurred with severely painful episodes. When a surgical treatment is not obvious, anti-seizure medications, such as gabapentin, phenytoin, and carbamazepine, and some antidepressants, like amitriptyline, are effective in managing the symptoms.
In neurosurgical operations near the skull base, there is a risk of cranial nerve injuries, including the glossopharyngeal nerve, which can be avoided with monitoring during the case. Electrical stimulation of nerve trunks and electromyographic recordings facilitate the identification of the cranial nerves before the operation starts. These techniques also monitor the cranial nerves during the surgical removal of tumors located at the skull base. As removal of the tumor progresses, the surgeon can make sure that surgical trauma to the nerve does not happen by observing for changes regarding the magnitude, shape, and contour of the responses.