Cranial Nerve V: Trigeminal

A 58-year-old retired town clerk presented with a 2-week history of numbness over her left chin and adjacent lower lip as well as vague pain in the left jaw. She explained that the area feels “Novacaine-like,” exactly like the sensation she had experienced numerous times recently because of extensive “dental work” requiring mandibular blocks. She reported a 5-year history of lichen planus of her left mandibular gingival mucosa, which was biopsied two or three times over the preceding several years. Two months earlier, she noted swelling and bleeding in the vicinity of one of the left lower molars. She was referred to an endodontist, who extracted the seemingly involved tooth. Because the bleeding and uncomfortable sensation in the area persisted, a biopsy was performed by an oral surgeon; this revealed a well-differentiated squamous cell carcinoma. Computed tomography (CT) of head and neck was requested by the surgeon, but the patient missed her appointments because of her husband's health issues. She otherwise enjoys good health.

Her exam revealed a 2-cm exophytic, ulcerated lesion in the left lower jaw area where the molar had been extracted. Examination of the cranial nerves demonstrated a quarter-sized area of numbness in the left chin and adjacent left lower lip. CT revealed a gingival mass invading the left mandible. Avid uptake in the mandible was noted on the positron emission tomography (PET) and bone scan images, which were obtained for staging purposes ( Fig. 7.1 ).

Comment: Although seemingly harmless, the complaint of numb chin requires careful evaluation as it is often a harbinger of malignancy. In a patient with known cancer of the facial skin or oral mucosa, as in this vignette, one has to consider invasion of the tumor into the mandible, causing bone destruction and involving the mental or inferior alveolar nerves. Naturally other branches of the trigeminal nerve can be affected by the same locally destructive process, causing numbness in the distribution of the implicated nerves. CT of the facial bones is usually diagnostic.