Ten pearls for improving your use of neuroimaging in neuro-ophthalmology

By Andrew G. Lee, MD

Professor of Ophthalmology, Neurology, and Neurosurgery
The H. Stanley Thompson Neuro-Ophthalmology Clinic

The University of Iowa Hospitals and Clinics

Iowa City, IA

1. Decide whether you need a computed tomography (CT) or magnetic resonance (MR) scan. The MR scan is superior to the CT scan for most neuro-ophthalmic indications but CT might still be the procedure of choice for the following ABCs: a. Acute study needed (e.g., subarachnoid or other bleed, trauma, hydrocephalus, emergent case); b. Bone (e.g., fracture, sinus disease, hyperostosis); or c. Calcification (e.g., meningioma, craniopharyngioma, retinoblastoma). In some patients (e.g., severe claustrophobia, metallic foreign body, aneurysm clip, pacemaker) an MR scan can not be performed and you will have to make do with a CT scan.

2. Decide if you need contrast or not. In general contrast material should be ordered for both CT and MR scans performed for neuro-ophthalmology. Contrast may not be absolutely necessary or even desirable in cases of acute hemorrhage (e.g., worst headache of my life, rule out subarachnoid hemorrhage), thyroid ophthalmopathy (i.e., “big muscles yes or no”), or in trauma cases. Although caution is necessary for iodinated contrast material in patients who might have worsening renal failure, screening renal function studies are necessary for patients with renal failure prior to gadolinium administration as well because of a rare side effect known as nephrogenic systemic dermatopathy. Consult your radiologist if questions.

3. Determine “where is the lesion” by topographically localize the lesion clinically, define the differential diagnosis (“what is the lesion”), establish the urgency of the imaging request, and then order the best study tailored to the lesion location (e.g. head, orbit, neck). You should communicate this information clearly and succinctly to the interpreting neuroradiologist on the order form.

4. Decide if you need specific imaging sequences to find what you are looking for (e.g. fat suppression and orbital post contrast study in optic neuropathy, fluid attenuation inversion recovery for white matter lesions of multiple sclerosis, gradient echo sequences for hemorrhage, diffusion weighted imaging for ischemic stroke) depending on clinical indication. Consult your radiologist in advance if you are unsure of the need for a special sequence or study.

5. Decide if you need to order any special imaging for specific vascular indications (e.g. MR angiography or CT angiography for third nerve palsy, MR venography for venous sinus thrombosis, or catheter angiography for aneurysm or AVM). It would be useful to establish your protocols in advance with the neuroradiologist rather than waiting until a live patient with the specific neuro-ophthalmic findings appears in your clinic emergently.

6. You should always consider picking up the phone and calling the radiologist if there is any doubt about localization, image study of choice, contrast selection or indications, or the final reading or report.

7. You should always go back to the patient if there is a mismatch between the clinical findings (e.g., bitemporal hemianopsia) and the imaging report. If the imaging shows either no abnormality or an abnormality that does not match the clinical localization then call up the radiologist or better yet, go down to the file room and review the films directly with the radiologist.

8. Ask questions of the radiologist if the quality of the imaging was sufficient, if the clinical area of interest was adequately imaged or not, if artifact might be obscuring the lesion, or if any additional studies might show the lesion.

9. If the clinical picture still suggests a specific lesion or localization and initial imaging report is “normal” then consider repeating the imaging with thinner slices and higher magnification of the area of interest especially if the clinical signs and symptoms are progressive. When in doubt throw away the report not the patient.

10. Always recognize that “clinical correlation required” is no joke and that the lack of an imaging abnormality does not exclude pathology in the patient. If in doubt consider referring to your local friendly neuro-ophthalmologist. In the words of a famous neuro-ophthalmologist, the field of neuro-ophthalmology has become the reinterpretation of supposedly “normal” imaging studies.

Reference
Modified from Lee AG, Brazis PW, Garrity J, White M. Imaging in orbital and neuro-ophthalmic disease. Am J Ophthalmol 2004; 138: 852-62.