Spectrum of Magnetic Resonance Imaging Features in Unilateral Optic Tract Dysfunction

Optic tract dysfunction may be the predominant or only clinical manifestation of an intracranial disorder including mass legion, ischemic infarct, inflammatory disease, and trauma. Documentation of the neuroimaging features of these lesions is limited to reports mostly published before the availability of MRI. This study was undertaken to document the spectrum of MRI features in patients presenting with optic tract dysfunction.

A retrospective study from 2004 to 2015 at a single tertiary care neuro-ophthalmology service of 24 patients who had unilateral optic tract dysfunction defined by a homonymous hemianopia and a relative afferent pupil defect that could not be attributed to optic neuropathy or retinopathy. Two institutional neuroradiologists, who were privy to the presence of optic tract dysfunction but not to its side or cause, independently documented the MRI abnormalities on a standard data collection form and then convened for a consensus review of the imaging abnormalities with the 2 clinician authors.

The clinical diagnoses were 6 ischemic strokes, 5 malignant brain tumors, 5 postoperative neurosurgical cases, 4 intracranial hemorrhages, 2 traumatic brain injuries, 1 midbrain/optic tract primary demyelination, and 1 temporal lobe herpes simplex encephalitis. In their independent review, both neuroradiologists identified MRI abnormalities in 20 (83%) cases that were extrinsic to the optic tract in the neighboring temporal lobe, midbrain, thalamus, basal ganglia, or suprasellar space. In 5 of those cases, the extrinsic abnormality included features suggesting compression of the optic tract, but these compressive features were not appreciated by either neuroradiologist until the consensus conference. In 15 cases, MRI abnormalities intrinsic to the optic tract itself were eventually identified, including T2 or fluid-attenuated inversion recovery image (FLAIR) hyperintensity (9 cases) or hypointensity (1 case), thinning (6 cases), thickening (2 cases), and contrast enhancement (1 case). However, none of these intrinsic MRI abnormalities was identified during the independent review, being detected only in the consensus conference.

Neuroradiologists aware of unilateral optic tract dysfunction but not of its side detected extrinsic (neighborhood) MRI abnormalities in most cases but did not appreciate that these extrinsic features sometimes included compression of the optic tract. MRI abnormalities intrinsic to the optic tract were entirely overlooked during independent review, being recognized only in a consensus conference with clinician authors. Neuroradiologists are more likely to detect MRI abnormalities pertinent to optic tract dysfunction once they have more complete clinical information and with higher resolution imaging, especially T1 postcontrast axial and coronal sequences and T2 or FLAIR coronal scans.