Clinical features and pathophysiological mechanism of the hemianoptic complication after the occipital transtentorial approach

Objective: To obtain detailed insight into neuro-ophthalmological characteristics and pathophysiology of hemianoptic complications after occipital transtentorial surgery. Methods: We reviewed the cases of 14 patients surgically treated by the occipital transtentorial approach. Treated lesions included 6 posterior third ventricle tumors, including pineal and tectal lesions, 3 falco-tentorial meningiomas, and 5 superior cerebellar lesions. The surgeries were performed by the unilateral occipital transtentorial approach with patients in the prone position. Results: Visual functions were preoperatively normal in all patients. After surgery, 11 patients (79%) showed hemianoptic complications detected by a confrontation test in the immediate postoperative period. The condition began to improve in the early postoperative days. The visual field recovered completely in 6 patients within 10 days, 2 patients recovered within 3 months, and 3 patients complained of permanent visual field defects. Optometric neuro-ophthalmic evaluation in the early postoperative period failed to detect complete homonymous hemianopsia, but homonymous inferior quadrantanopia and scotomatous defects were observed in 6 patients. These visual field defects were permanent in 3 patients. Postoperative MRI showed no morphological abnormality except these three patients. Atrophic change of the occipital lobe with preservation of striate cortex was associated with persistent visual field defects in two patients. Cerebral blood flow evaluation by single photon emission computed tomography suggested that temporary local hyperperfusion of the retracted occipital region when visual field defect was present. Conclusion: Hemianoptic visual field defects can recover via inferior quadrantanopia or scotomatous defect. All of these defects are attributable to injury to the optic radiation as well to the occipital lobe. Hyperperfusion of the retracted occipital region may underlie the pathophysiology of hemianoptic complications after the occipital transtentorial approach.