In patients with clinical features of hemifacial spasm, MRA can be complementary to 3-D heavily T2-weighted MRI sequences for characterizing the anatomy of vascular loops potentially compressing the centrally myelinated portion of the facial nerve with sensitivity and accuracy reported as >95% and a good correlation with surgical findings [76,109,110]. Volumetric and 3T imaging have been reported to provide improved visualization of the facial nerve and its surrounding perineural vascular plexus [7,19,111,113]. In general, Bell palsy patients need not be imaged unless the symptoms are atypical, recurrent, or persist for 2 to 4 months [102]. When imaging is considered, MRI is the method of choice. Variable abnormal enhancement patterns may be seen in the canalicular, labyrinthine, geniculate, tympanic, and mastoid portions of the nerve [106,117-122]. There is a lack of consensus regarding the prognostic value of MRI in Bell palsy [118-121], and MRI is most useful for excluding other causes of facial nerve palsy. High-resolution thin-cut contrast-enhanced MRI is an especially useful method to evaluate for perineural spread of a tumor, which can affect CN VII and is discussed in Variant 10. Sensitivities for MRI detection of perineural spread of a tumor range from 73% to 100% and vary according to the nerve evaluated and timing of imaging relative to tissue sampling [65,104,123-125]. In patients with clinical features of hemifacial spasm, 3-D heavily T2-weighted MRI sequences and MRA are noninvasive methods for characterizing the anatomy of vascular loops potentially compressing the centrally myelinated portion of the facial nerve and correlate well with surgical findings [76,78,100,101,110]. 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 Cranial Neuropathy decompression [78,100].
Cranial Neuropathy. In patients with clinical features of hemifacial spasm, MRA can be complementary to 3-D heavily T2-weighted MRI sequences for characterizing the anatomy of vascular loops potentially compressing the centrally myelinated portion of the facial nerve with sensitivity and accuracy reported as >95% and a good correlation with surgical findings [76,109,110]. Volumetric and 3T imaging have been reported to provide improved visualization of the facial nerve and its surrounding perineural vascular plexus [7,19,111,113]. In general, Bell palsy patients need not be imaged unless the symptoms are atypical, recurrent, or persist for 2 to 4 months [102]. When imaging is considered, MRI is the method of choice. Variable abnormal enhancement patterns may be seen in the canalicular, labyrinthine, geniculate, tympanic, and mastoid portions of the nerve [106,117-122]. There is a lack of consensus regarding the prognostic value of MRI in Bell palsy [118-121], and MRI is most useful for excluding other causes of facial nerve palsy. High-resolution thin-cut contrast-enhanced MRI is an especially useful method to evaluate for perineural spread of a tumor, which can affect CN VII and is discussed in Variant 10. Sensitivities for MRI detection of perineural spread of a tumor range from 73% to 100% and vary according to the nerve evaluated and timing of imaging relative to tissue sampling [65,104,123-125]. In patients with clinical features of hemifacial spasm, 3-D heavily T2-weighted MRI sequences and MRA are noninvasive methods for characterizing the anatomy of vascular loops potentially compressing the centrally myelinated portion of the facial nerve and correlate well with surgical findings [76,78,100,101,110]. 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 Cranial Neuropathy decompression [78,100].