Something Got Your Tongue? A Unique Cause of Hypoglossal Nerve Palsy

Introduction The authors report a rare cause of isolated hypoglossal nerve palsy caused by a high cervical osteophyte. This case increases clinical knowledge of an underreported condition and teaches the clinician radiologic pearls in making the diagnosis. To their knowledge, this is the first case report showing surgical remediation of this condition. Symptoms and Clinical Findings. A 73-year-old female presented with several months of occipital headache, progressive dysarthria, dysphagia, and tongue deviation to the right. Her neurologic exam was significant for atrophy of the right hemitongue with tongue fasciculations. On protrusion, her tongue deviated rightward. Diagnosis and Therapeutic Intervention. Careful review of her initial head computed tomography (CT) imaging revealed that a high cervical osteophyte caused unilateral, isolated hypoglossal nerve palsy. Neurosurgery performed a right, far lateral approach for decompression of this osteophyte and over the ensuing months her symptoms improved. Conclusion High cervical osteophyte is an underrecognized cause of isolated hypoglossal nerve palsy. The imaging investigation should be systematic and focus on the skull base with magnetic resonance imaging (MRI) or CT. This is a rare occasion when high resolution CT of the skull base can actually be the more helpful imaging modality. As shown in this case, an osteoarthritic cause can be surgically ameliorated.


Case
A 73-year-old woman with a history of osteoarthritis and hypertension complained of a chronic but progressive right occipital headache and was developing problems with her tongue. Six weeks prior to presentation, she noticed uncoordinated tongue movements, tongue deviating right on protrusion, and dysarthria. She had difculty manipulating a food bolus in her mouth and continually bit her right cheek and tongue. Subsequently she had lost ten pounds. She denied facial weakness, ptosis, diplopia, facial sensory changes, or taste perversion.
Her neurologic exam was signifcant for atrophy of the right hemitongue with tongue fasciculations. On protrusion, her tongue deviated rightward. Taste was preserved. Te remainder of her cranial nerve, facial motor, and peripheral motor exam, including muscle bulk and tone were normal. Tere were no peripheral fasciculations. Sensory exam and refexes were normal.
Without detailed history of tongue weakness, an initial noncontrast head CT was read as normal. MRI brain with and without contrast showed atrophy of the right tongue associated with subtle fatty infltration and T2 hyperintensity suggestive of denervation atrophy. Lumbar puncture and erythrocyte sedimentation rate were normal. Electromyography (EMG) with nerve conduction study was performed to evaluate for more difuse neuromuscular disease. Te only abnormal fnding on EMG was a subacute right hypoglossal neuropathy.
After reviewing the head CT and MRI with neuroradiology and including clear clinical information, degenerative osteophytes were seen projecting from the right atlanto-occipital joint laterally to the adjacent right carotid space, best seen on the CT (Figures 1(a)-1(c)). Te osteophyte could be seen at the exit of the right hypoglossal canal on axial MRI images but it was much more difcult to visualize ( Figure 2).
Based on our patient's workup, we concluded that she had an isolated hypoglossal nerve palsy from an atlanto-occipital osteophyte compressing the nerve as it exited the hypoglossal canal. Neurosurgery was consulted. To decompress the nerve and stabilize her condition, surgery was indicated.
Te patient was taken to the operating room for a right, far lateral approach for decompression of this osteophyte. Subperiosteal dissection was used to expose the suboccipital bone and the mastoid bone. Te high-speed drill was used to turn a suboccipital craniotomy and perform a partial mastoidectomy to decompress the sigmoid sinus and the jugular bulb. Te high cervical region was then dissected. Te occipital and C1 condyles were exposed and the drill was used to resect the condyle down to the level of the hypoglossal canal. Tis decompressed the hypoglossal nerve adequately without having to remove the osteophyte. Te dura was then closed in a water tight fashion. Te bone was replaced using the plating system. Te muscles were reapproximated. Te scalp was then closed in layers. Postoperative CT is shown in Figure 3.
She noticed improvement within months that has persisted over 3 years. Her tongue function including eating and swallowing was much improved. Te right half of her tongue was less atrophic. Te tongue now protruded midline. Her right occipital headache had resolved. Only some mild numbness around her surgical scar remained. From her   Case Reports in Neurological Medicine perspective, she was pleased with the surgical outcome. To the best of our knowledge, this is the frst described surgically ameliorated case of hypoglossal nerve palsy caused by high cervical osteophyte.

Discussion
Hypoglossal nerve injury is not uncommon when it occurs with other lower cranial nerve palsies [1], but isolated hypoglossal nerve palsy is rare. Isolated hypoglossal nerve palsy has been previously reviewed [2,3]. Te best way to ascertain the cause of hypoglossal nerve injury is to use an anatomical segmental approach. By subdividing the course of the hypoglossal nerve into fve sections (brain stem, premedullary cistern, skull base/hypoglossal canal, nasopharyngeal/carotid area, and sublingual area), the number of diferential causes in each area becomes more manageable and easier for the clinician to remember [3]. Te most common cause of isolated hypoglossal nerve palsy is skull base tumor (either metastasis or primitive malignant or benign tumor), accounting for up to 50% of cases [2,3]. Cranial trauma producing occipital condyle fracture is the second most common cause. Tis cranial trauma tends to occur in two ways-deceleration trauma from road accidents [4] or surgical trauma. Te most common surgical injury is neck surgery or prolonged cervical hyperextension during anesthesia [3]. Te third most common cause of isolated hypoglossal injury is internal carotid artery dissection. Cervical rheumatoid arthritis and cervical osteophytes from osteoarthritis have been more rarely implicated [5][6][7]. In children and adolescents, infectious mononucleosis should be investigated [2].
More modern case series are questioning if hypoglossal nerve palsy caused by craniocervical junction (CCJ) degenerative disease is an under-recognized entity because of provider unawareness compounded by difculty in identifying the ofending lesions on initial CT or MRI standard formats [7]. Tis was highlighted by our case. Alerting the radiologist to one's suspicion of this diagnosis is critical so they can dedicate attention to the skull base and perform CT reconstructions if necessary. A retrospective series from the Mayo Clinic of 18 patients with hypoglossal nerve palsy from CCJ degenerative disease concluded that a small feld of view; thin-section (≤2 mm) axial, coronal, and sagittal soft tissue; and bone reconstructions centered at the hypoglossal canal are more efective at identifying the ofending CCJ degenerative disease [7].
Te imaging investigation should be systematic and focus on the skull base with MRI or CT [1]. Tis is one of those rare occasions when high resolution CT of the skull base can actually be the more helpful imaging modality. Tis was the case with our patient. As shown in our case, an osteoarthritic cause can be surgically ameliorated. Te patient was pleased at the improvement in most neurologic symptoms and resolution of her right occipital headache. Since the osteophyte was left in place postoperatively, the headache was likely due to associated CCJ degenerative disease and improved after the surgery. Retrospective case series of 18 patients with hypoglossal nerve palsy from CCJ degenerative disease identifed major associated complaint of new or worsening headache or suboccipital pain in 13 of 18 patients [7]. Her timely presentation and surgery within two months of symptom onset likely contributed to the favorable outcome.

Data Availability
Te clinical data used to support the fndings of this study are included within the article. Case Reports in Neurological Medicine 3