Diplopia due to skew deviation following neurotologic procedures

Introduction: Diplopia following cerebellopontine angle (CPA) surgery is usually attributed to neuropathy of III, IV or VI cranial nerves. Diplopia in the absence of cranial neuropathy following CPA surgery is rare. We present a series of patients who developed vertical diplopia from skew deviation following resection of tumors in the CPA or labyrinthectomy. Primarily associated with brainstem lesions, this vertical misalignment of the visual axis is postulated to result from unilateral disruption of supranuclear input from the otolithic organs. Methods: Retrospective review of patients with complaints of diplopia following CPA surgery. Patients underwent neuroophthalmologic consultation and examination, including opticokinetic testing, confrontational visual field assessment, color plate, pupillary reflex, slit lamp examination and Head Tilt Test. Results: Four patients with residual hearing preoperatively developed skew deviation immediately following surgical intervention, including translabyrinthine(n=1) and retrosigmoid (n=2) approaches to the CPA and labyrinthectomy (n=1). Neuroophthalmologic exam demonstrated intact extraocular movements, and 2-14 mm prism diopter hypertropia on both primary gaze and Head Tilt Testing. In all cases, skew deviation resolved spontaneously with normalization of the neuroophthalmologic examination within 10 weeks. Conclusion: Patients undergoing CPA surgery or labyrinthectomy can develop postoperative diplopia due to skew deviation as a consequence of acute vestibular deafferentation. Patients with significant hearing preoperatively, a probable marker for residual vestibular function, may be specially at risk for developing skew deviation. As vestibular ablation occurs routinely with each of these procedures, skew deviation likely occurs more frequently than is currently diagnosed. Complaints of diplopia should prompt neuro-ophthalmologic consultation to reliably diagnose skew deviation and exclude cranial neuropathy. Patients can be reassured as spontaneous resolution typically occurs within 10 weeks.