Diagnostic Approach for Combined 3rd and 6th Nerve Palsy with Pupil Sparing

Localization of the Lesion

Multiple ipsilateral cranial nerve palsies affecting cranial nerves III and VI suggest a lesion at the cavernous sinus or orbital apex, according to the American College of Radiology 1, 2
The combination of decreased vision with diplopia and cranial nerve palsies further supports localization to the cavernous sinus or orbital apex, as pathology in these locations can affect both ocular motility and visual function, as stated by Ophthalmology 3
Pupil-sparing in a third nerve palsy typically suggests a microvascular etiology, but when combined with 6th nerve palsy and vision loss, a compressive, infiltrative, or inflammatory lesion is more likely, according to Ophthalmology 3

MRI with contrast is the preferred imaging modality for this presentation as it provides superior evaluation of the cranial nerves, cavernous sinus, and orbital apex, recommended by the American College of Radiology 1, 5
High-resolution T2-weighted images focused on the cranial nerves should be included in the imaging protocol to better visualize the nuclear, cisternal, and skull-base cranial nerve segments, as suggested by the American College of Radiology 1

Vascular imaging with MRA should be considered as a complement to the contrast-enhanced MRI to evaluate for possible vascular compression, particularly if aneurysm is suspected, according to the American College of Radiology 1, 5
If a mass lesion is identified near the cavernous sinus, additional MRV (magnetic resonance venography) may be indicated to assess the integrity of the dural venous sinus, as recommended by the American College of Radiology 5

Cavernous sinus pathology: meningioma, schwannoma, metastatic lesions, inflammatory or infectious processes, as listed by Ophthalmology and the American College of Radiology 2, 3
Orbital apex syndrome: tumors, inflammatory disease, infection, according to the American College of Radiology 1, 5
Basilar subarachnoid space pathology: infectious meningitis or non-infectious causes, as stated by the American College of Radiology 2