Unfortunately, if you notice acute atrophy over only one side of the head, it’s most likely a trigeminal nerve sheath tumor. The trigeminal nerve (cranial nerve V) has three major branches. It supplies a mainly sensory input to a lot of places on the face- like the eyes, upper and lower jaw via the ophthalmic and the maxillary and mandibular branches. But it also provides motor input to the muscles of mastication: temporalis, masseter, and pterygoids. When motor input is cut, muscles...