3D Gadolinium-Enhanced CISS for the Diagnosis of Ischemic Third Nerve Palsy.

BACKGROUND AND PURPOSE: Microvascular ischemic neuropathy is a common cause of third nerve palsy (TNP) in adults. Gadolinium enhancement of the intracavernous segment of the third cranial nerve (CNIII) has been previously reported in this context. Given the high spatial resolution of the 3D CISS sequence for analyzing the cavernous sinus, our objective was to evaluate the diagnostic accuracy of intracavernous third nerve changes on 3D contrast-enhanced CISS in differentiating microvascular ischemic TNP from other etiologies. MATERIALS AND METHODS: We conducted a single-center retrospective case-control study involving patients presenting with isolated TNP at the emergency department between 2018 and 2022, where all of whom underwent 3T MRI, including a 3D contrast-enhanced CISS sequence. Based on clinical examination and paraclinical investigations, a neurologist and an ophthalmologist jointly established the etiology of TNP during the initial patient care. Patients diagnosed with microvascular ischemic TNP were matched with a control group of TNP from other etiologies. Two radiologists independently assessed contrast enhancement and thickening of the intracavernous third nerve on the 3D contrast-enhanced CISS without knowledge of the etiological diagnosis. Sensitivity and specificity for diagnosing microvascular ischemic TNP were calculated. RESULTS: Fifty-four patients were included: 27 with microvascular ischemic TNP and 27 controls (59% men, mean age 72 years). The control group comprised TNP of inflammatory (18%), infectious (18%), aneurysmal (16%), tumoral (11%), stroke-related (22%), and undetermined (15%) origins. Contrast enhancement and thickening of the intracavernous third nerve were more frequent in microischemic TNP compared with the control group (78% versus 52%, P = .046, and 67% versus 27%, P = .003, respectively). The combination of contrast enhancement and nerve thickening demonstrated a sensitivity of 67% and a specificity of 74% for diagnosing microvascular ischemic TNP. CONCLUSIONS: Detection of contrast enhancement and thickening of the intracavernous third nerve by using the 3D contrast-enhanced CISS sequence on 3T MRI is significantly more frequent in microvascular ischemic TNP than in TNP from other etiologies. Though not specific, these findings may support this diagnosis when accompanied by supportive clinical features.