In a retrospective review of the literature comparing test performance of MRI/MRA with CTA in the assessment of cervicocephalic arterial dissection with a reference standard of catheter angiography, the authors report MRI sensitivities and specificities of 50% to 79% and 67% to 99%, respectively, and CTA sensitivities and specificities of 51% to 98% and 67% to 100%, respectively (based on prospective studies) [188]. The authors concluded that the test characteristics of MRI/MRA and CTA for diagnosis of cervicocephalic arterial dissection were similar and study selection should be based on individual factors including urgency of imaging. Limitations of the literature assessing MRA and CTA for dissection include most studies evaluate test performance in the clinical setting of traumatic dissection rather than spontaneous dissection. CTA is often used as a primary screening tool when carotid dissection is suspected in the emergent setting [186]. Thin-cut heavily T2-weighted contrast-enhanced modified balanced SSFP sequences and contrast-enhanced MRA focused on the posterior skull provide detailed imaging of the lower nerves within the jugular foramen, and their relationship to the hypoglossal nerve as they exit the skull base, with 90% to 100% of imaged CN IX, CN X, and CN XII visible [24]. There is variable direct visualization of CN XI with the cranial segment identified in 88% of the sides and the spinal segment identified in 93% of the sides in one study [149]. Another study reported lower rates with the spinal root of CN XI visualized in only 51% of subjects using heavily T2-weighted contrast-enhanced modified balanced SSFP sequences [24]. Cranial Neuropathy DWI can be used to assess for acute brainstem infarction, cholesteatoma, and for characterizing tumor cellularity. False-negative DWI can occur in the setting of very small ischemic brainstem infarcts [137,138].
Cranial Neuropathy. In a retrospective review of the literature comparing test performance of MRI/MRA with CTA in the assessment of cervicocephalic arterial dissection with a reference standard of catheter angiography, the authors report MRI sensitivities and specificities of 50% to 79% and 67% to 99%, respectively, and CTA sensitivities and specificities of 51% to 98% and 67% to 100%, respectively (based on prospective studies) [188]. The authors concluded that the test characteristics of MRI/MRA and CTA for diagnosis of cervicocephalic arterial dissection were similar and study selection should be based on individual factors including urgency of imaging. Limitations of the literature assessing MRA and CTA for dissection include most studies evaluate test performance in the clinical setting of traumatic dissection rather than spontaneous dissection. CTA is often used as a primary screening tool when carotid dissection is suspected in the emergent setting [186]. Thin-cut heavily T2-weighted contrast-enhanced modified balanced SSFP sequences and contrast-enhanced MRA focused on the posterior skull provide detailed imaging of the lower nerves within the jugular foramen, and their relationship to the hypoglossal nerve as they exit the skull base, with 90% to 100% of imaged CN IX, CN X, and CN XII visible [24]. There is variable direct visualization of CN XI with the cranial segment identified in 88% of the sides and the spinal segment identified in 93% of the sides in one study [149]. Another study reported lower rates with the spinal root of CN XI visualized in only 51% of subjects using heavily T2-weighted contrast-enhanced modified balanced SSFP sequences [24]. Cranial Neuropathy DWI can be used to assess for acute brainstem infarction, cholesteatoma, and for characterizing tumor cellularity. False-negative DWI can occur in the setting of very small ischemic brainstem infarcts [137,138].