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 a tumor [129,130]. 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 do not need to be imaged unless the symptoms are atypical, recurrent, or persistent 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].
Cranial Neuropathy. 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 a tumor [129,130]. 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 do not need to be imaged unless the symptoms are atypical, recurrent, or persistent 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].