Trigeminal neuropathy secondary to a meningioma.

A 45-year-old man complained of weakness while chewing and decreased hearing. His hearing loss had been caused by serous otitis media, secondary to eustachian tube dysfunction that had been attributed to a malfunction of the tensor palatini muscle. Magnetic resonance imaging (MRI) revealed a homogeneously enhanced mass in the area of the right cavernous sinus. In addition, there was a marked atrophy of the muscles of mastication and a severe degree of fatty infiltrate on the ipsilateral side (figure).

Atrophy resulting from injury to the mandibular branch (V3) occurs in two distinct patterns, depending on whether the involvement is distant or proximal along the course of V3. The distal portion of branch V3 is located between the take-off of the masticator nerve from the main trunk of V3 and the origin of the mylohyoid nerve from the inferior alveolar nerve. When injury to the nerve is distal, only the muscles innervated by the mylohyoid nerve (anterior belly of the diagastric and mylohyoid muscles) are affected. [1] When an injury is proximal to the masticator nerve take-off, all muscles innervated by V3 will be affected, including the muscles of mastication, as was the case with our patient.

Reference

(1.) Harnsberger HR. The upper cranial nerves. In: Harnsberger HR. Handbook of Head and Neck Imaging. 2nd ed. St. Louis: Mosby, 1995:459-87.