Both false- positive and false-negative imaging studies occur when assessing for neurovascular contact in the setting of hemifacial spasm; consequently MRI is supportive rather than diagnostic in selecting candidates for microvascular decompression [78,100]. In patients with failed initial microvascular decompression surgery, heavily T2-weighted MRI may be helpful to delineate the cause [101]. DTI is an advanced imaging technique that may be useful in assessing the facial nerve. Several studies suggest that DTI is accurate for the preoperative localization of the cisternal facial nerve to avoid iatrogenic injury in patients with cerebellopontine angle tumors [107,126-128]. Research indicates that DTI may have future use localizing the intraparotid facial nerve and detecting perineural spread of tumor [129,130]. US Neck There is no relevant literature to support the use of US neck in the evaluation of isolated unilateral facial nerve palsy or hemifacial spasm. Variant 4: Multiple different middle cranial nerve palsies (CN V-VII). Initial imaging. Multiple CN nuclei are closely approximated within the brainstem, from which motor fibers originate and sensory fibers terminate. A small single brainstem lesion can produce severe and mixed neurologic deficits, including multiple cranial neuropathies, often times with some component of cerebellar, motor, or somatosensory deficit helping in clinically localizing the lesion. The pons connects the midbrain to the medulla. The dorsal pontine tegmentum contains white matter tracts and CN V through CN VIII nuclei, and the ventral pons contains corticospinal, corticobulbar, and corticopontine tracts [1,131]. After exiting the pons, the first and second divisions of the trigeminal nerve course along the lateral wall of the cavernous sinus, the abducens nerve courses through the cavernous sinus, and CNs VII and VIII extend through the cerebellopontine angle toward the porus acusticus. The third division of the trigeminal exits the skull base via foramen ovale.
Cranial Neuropathy. Both false- positive and false-negative imaging studies occur when assessing for neurovascular contact in the setting of hemifacial spasm; consequently MRI is supportive rather than diagnostic in selecting candidates for microvascular decompression [78,100]. In patients with failed initial microvascular decompression surgery, heavily T2-weighted MRI may be helpful to delineate the cause [101]. DTI is an advanced imaging technique that may be useful in assessing the facial nerve. Several studies suggest that DTI is accurate for the preoperative localization of the cisternal facial nerve to avoid iatrogenic injury in patients with cerebellopontine angle tumors [107,126-128]. Research indicates that DTI may have future use localizing the intraparotid facial nerve and detecting perineural spread of tumor [129,130]. US Neck There is no relevant literature to support the use of US neck in the evaluation of isolated unilateral facial nerve palsy or hemifacial spasm. Variant 4: Multiple different middle cranial nerve palsies (CN V-VII). Initial imaging. Multiple CN nuclei are closely approximated within the brainstem, from which motor fibers originate and sensory fibers terminate. A small single brainstem lesion can produce severe and mixed neurologic deficits, including multiple cranial neuropathies, often times with some component of cerebellar, motor, or somatosensory deficit helping in clinically localizing the lesion. The pons connects the midbrain to the medulla. The dorsal pontine tegmentum contains white matter tracts and CN V through CN VIII nuclei, and the ventral pons contains corticospinal, corticobulbar, and corticopontine tracts [1,131]. After exiting the pons, the first and second divisions of the trigeminal nerve course along the lateral wall of the cavernous sinus, the abducens nerve courses through the cavernous sinus, and CNs VII and VIII extend through the cerebellopontine angle toward the porus acusticus. The third division of the trigeminal exits the skull base via foramen ovale.