Conditions: lingual nerve dysfunction
Alteration in sense of touch of the tongue and/or taste
The lingual nerve, shown in yellow, transmits taste and touch sensation from the tongue to the brain, and it also controls saliva production from the submandibular and (not shown) sublingual salivary glands. Click to enlarge.
A posterior view demonstrating the lingual nerve, submandibular and sublingual glands, and floor of mouth muscles. From: Netter FH. Atlas of Human Anatomy. Click to enlarge.
The lingual nerve, shown in yellow, is shown coursing along the underside (ventral aspect) of the tongue. Source: Henry Vandyke Carter, Public domain, via Wikimedia Commons. Click to enlarge.
What is the Lingual nerve?
The left and right lingual nerves, each a branch of the trigeminal (fifth) cranial nerve, provide taste and general sensation (touch and temperature) to each half of the tongue. A lingual nerve also controls the rate of secretion of saliva from the submandibular and the sublingual salivary glands on its side. Taste consists of sweet, salty, sour, bitter, and umami sensations. Umami is a taste reminiscent of chicken broth. Flavor, the overall sensation of a food, is a combination of taste and smell, and smell information is transmitted to the brain separately through the olfactory nerve. The taste fibers of the nerve travel toward the brain within the lingual nerve proper until the taste fibers branch away from this nerve to form the chorda tympani nerve, which courses through the middle ear before joining the main trunk of the facial (seventh) cranial nerve and traveling to the brainstem. The lingual nerve serves only the front (anterior) 2/3rds of the tongue, as touch and the lesser taste functions of the back (posterior) 1/3 of the tongue are governed by other nerves, such as cranial nerves 9, and 10.
Why is the lingual nerve affected by surgery?
Several surgical operations require dissection in proximity to the lingual nerve. Similarly, the chorda tympani nerve, which runs with the facial (seventh) cranial nerve before branching and joining the trigeminal (fifth) cranial nerve, is anatomically where specific operations require dissection. Submandibular and sublingual gland surgery, for example, involve dissection of this nerve. Mandible surgery, especially at the angle of the mandible, involves instrumentation close to this nerve. Surgery of the ear, such as middle ear and mastoid surgery, also include close contact with the chorda tympani nerve. Cancer operations may require sacrifice (cutting) of the nerve for the purpose of removing a cancer entirely.
Additionally, several surgical operations require that pressure be placed on the tongue in order to retract it for adequate access and exposure to the surgical site, such as the tonsils or other sites in the throat, larynx, esophagus, or trachea. Despite efforts to use only the required degree of pressure on the tongue and to intermittently remove pressure on the tongue to allow for blood flow, lingual nerve dysfunction may still occur as a result of such surgical maneuvers.
What are the symptoms of lingual nerve dysfunction?
Dysfunction of a lingual nerve (or the fibers of the chorda tympani nerve) can cause an alteration of taste. Since the tongue has a left and right lingual nerve, complete loss of one lingual nerve does not cause complete loss of taste. Often, shortly after a lingual nerve is injured, an individual may experience a metallic taste, but fortunately this sensation tends to fade and taste may return to near normal after some months. The general sensation function of the lingual nerve, informing the brain of touch and temperature, can lead to numbness of the affected side of the tongue in its front (anterior) portion. Over time, the degree of numbness often decreases, as nerve fibers from the injured nerve or from the opposite lingual nerve grow into the affected side and provide some touch and temperature sensation again. Since the lingual nerve also affects the rate of saliva production from the same side submandibular and sublingual nerves, an injury of the nerve fibers going to these glands may decrease saliva production. Fortunately, with six major salivary glands and thousands of minor salivary glands, an individual typically would not experience a drier mouth in this situation.
What precautions are necessary with lingual nerve dysfunction?
Unintentional biting of the tongue with consequent trauma is a risk with tongue numbness, as a numb tongue might feel to the teeth like food. If a severe alteration in taste were to occur, extra care to avoid eating potentially spoiled foods may be necessary.
HOw is lingual nerve injury prevented?
While the course of an individual’s lingual nerve is unique, surgeons know the anatomy and make every effort to avoid any injury to the nerve during dissection. Some procedures require pressure on the tongue, which also may cause dysfunction of the lingual nerve. Despite all efforts, sometimes injury to the lingual nerve is unavoidable.
How much will lingual nerve dysfunction bother someone?
Lingual nerve dysfunction may resolve after a period of time (sometimes up to a year), but even when it does not resolve, the degree of bother to an individual tends to become less over time as compensation develops.