Bifurcated optic radiation tractography using diffusion tensor imaging in a patient with traumatic brain injury: A case report.

RATIONALE

Visual field deficits can occur in up to 60% of traumatic brain injury (TBI) cases. The Humphrey visual fields test and visual-evoked potential studies (VEPs) are common diagnostic tools but rely on patient's participation and can be affected by external factors. Diffusion tensor imaging (DTI) and diffusion tensor tractography (DTT) can provide an objective alternative to evaluating optic radiation (OR) injury. Although previous studies have examined the OR by categorizing it into only left and right tracts, we demonstrate the feasibility of assessing OR injury by subdividing each side into upper and lower regions in a patient with visual field deficits following TBI using DTI and bifurcated DTT.

PATIENT CONCERNS

In June 2013, a 40-year-old man fell down the stairs, resulting in a large right frontotemporal epidural hemorrhage, a small contusional hemorrhage, and a left frontotemporoparietal subdural hemorrhage. He underwent an emergency decompressive craniectomy. Following the accident, he reported blurred peripheral vision in both eyes. Six years later, he visited the outpatient clinic due to continuous visual impairment.

DIAGNOSES

He had right upper and left lower quadrantanopsia resulting from OR injury secondary to TBI.

INTERVENTIONS

DTI data were acquired 6 years after TBI onset.

OUTCOMES

Four ORs from the patient and 8 healthy controls were reconstructed using DTI and DTT. We set the seed region of interest on the lateral geniculate nucleus, and the target region of interest on the occipital pole along the upper and lower lips of the calcarine fissure, bilaterally. As a result, we divided the ORs into 4 regions; upper right, lower right, upper left, and lower left. The patient's right upper and left lower ORs showed significantly higher mean diffusivity values and lower tract volume values compared to controls, as well as narrower neural fibers on DTT compared with healthy controls. This finding aligns with the Humphrey visual fields test results, which indicated right upper and left lower quadrantanopsia in the patient.

LESSONS

This case demonstrates that DTI and DTT provide an objective assessment of OR injury, independent of patient cooperation. A refined 4-tract OR analysis can allow for more precise assessment of OR injury, potentially enabling the identification of quadrantanopsia.