How Much Tongue Can Be Removed Without Affecting Function?
speech and swallow will be affected.
The answer to this question depends on 3 main factors.
• What orientation is the tongue removed?
• How much is removed?
• Will nerve function be preserved? The nerve is what makes the tongue move (specifically cranial nerve 12 called the hypoglossal nerve)
Regardless of how much or little of the tongue gets removed, if nerve function is lost, speech and swallow will be affected. As such, when tongue resection is performed, extreme care is taken to preserve nerve function and not to accidentally cut the hypoglossal nerve unless absolutely necessary (the nerve is invaded by cancer). As an FYI, this nerve is about 1.75cm off to the side of the tongue's midline.
When tongue removal is performed on the SIDE of the tongue, up to 1/3 of it can be removed without significant speech or swallow deficits ASSUMING nerve function remains intact and tongue tip is left alone. If more than 1/3 is removed, some degree of reconstruction will be required involving taking skin and muscle from the forearm to fill the space lost to the tongue resection (procedure is called radial forearm free flap).
If the tongue tip is removed, far less can be lost before it will start to affect speech. Why? Because the tongue tip is used to help articulate words. How much can be removed before it starts to affect speech depends on the tongue length and shape. Swallow is typically unaffected.
Typically tongue tip removal occurs through trauma when it may get bitten off during a seizure or bitten off by another individual as occurred to this man whose tongue tip was bitten off by his girlfriend when he tried to kiss her. [link]
Side of the tongue removal usually occurs through surgical excision due to cancer concerns.
As an aside, there is another type of tongue removal procedure used to address obstructive sleep apnea where the central back part of the tongue is removed. This procedure is performed when the tongue is large and causes obstruction while a person is sleeping. If properly performed, no speech or swallow deficits will occur.
Read more about this procedure here.