Hypoglossal nerve palsy can also be accompanied by variable palsies of the glossopharyngeal (CN IX), vagus (CN X), and accessory nerves (CN XI) in combined syndromes, particularly from lesions arising in the brainstem or jugular foramen, as discussed in Variant 9 [183]. CT Head There is no relevant literature to support the use of routine CT head alone in the initial evaluation of unilateral isolated CN XII palsy. CT Maxillofacial There is no relevant literature to support the use of maxillofacial CT in the initial evaluation of unilateral isolated CN XII palsy. CT Temporal Bone There is no relevant literature to support the use of temporal bone CT in the initial evaluation of unilateral isolated CN XII palsy. CT Neck Evaluation of the entire course of the hypoglossal nerve is required with a hypoglossal nerve palsy. MRI is useful for evaluating hypoglossal nerve palsy, directly imaging the brainstem, the intracranial and skull base segments of the hypoglossal nerve and assessing for possible lesions along the extracranial segments of the nerve while providing improved soft tissue contrast [5,13,181,183,189]. The extracranial segment of the hypoglossal nerve within the suprahyoid neck is difficult to see with MRI and CT and inferred by knowledge of the nerve course and surrounding anatomy. Neck CT provides complementary information to MRI, characterizing the osseous integrity of the hypoglossal canal and surrounding skull base [183]. Imaging protocols should include thin-cut high-resolution bone windows through the posterior skull base. Contrast should be administered, because tumors are the most common cause of isolated hypoglossal nerve palsy in this segment. Noncontrast CT may also be an alternate option for this clinical scenario. There is no relevant literature to support the use of combined pre- and postcontrast imaging.
Cranial Neuropathy. Hypoglossal nerve palsy can also be accompanied by variable palsies of the glossopharyngeal (CN IX), vagus (CN X), and accessory nerves (CN XI) in combined syndromes, particularly from lesions arising in the brainstem or jugular foramen, as discussed in Variant 9 [183]. CT Head There is no relevant literature to support the use of routine CT head alone in the initial evaluation of unilateral isolated CN XII palsy. CT Maxillofacial There is no relevant literature to support the use of maxillofacial CT in the initial evaluation of unilateral isolated CN XII palsy. CT Temporal Bone There is no relevant literature to support the use of temporal bone CT in the initial evaluation of unilateral isolated CN XII palsy. CT Neck Evaluation of the entire course of the hypoglossal nerve is required with a hypoglossal nerve palsy. MRI is useful for evaluating hypoglossal nerve palsy, directly imaging the brainstem, the intracranial and skull base segments of the hypoglossal nerve and assessing for possible lesions along the extracranial segments of the nerve while providing improved soft tissue contrast [5,13,181,183,189]. The extracranial segment of the hypoglossal nerve within the suprahyoid neck is difficult to see with MRI and CT and inferred by knowledge of the nerve course and surrounding anatomy. Neck CT provides complementary information to MRI, characterizing the osseous integrity of the hypoglossal canal and surrounding skull base [183]. Imaging protocols should include thin-cut high-resolution bone windows through the posterior skull base. Contrast should be administered, because tumors are the most common cause of isolated hypoglossal nerve palsy in this segment. Noncontrast CT may also be an alternate option for this clinical scenario. There is no relevant literature to support the use of combined pre- and postcontrast imaging.