Electroretinography during embolization of an ophthalmic arteriovenous fistula
A 17-year-old right handed male initially presented to his primary care physician with a 4-year history of a growing pulsatile midline scalp mass just behind the hairline. Initially suspected to be a cyst, it was biopsied resulting in significant bleeding. Subsequently, computed tomography angiography demonstrated a vascular scalp lesion and he was referred to the senior author. Digital subtraction angiography (DSA) showed a dural AVF supplied by bilateral superficial temporal, ophthalmic, and the right middle meningeal arteries. The AVF drained via the facial vein into the internal jugular vein. The pulsatile lesion was aesthetically displeasing to the patient and painful with palpation. After discussing the various treatment options including observation alone, it was decided that the AVF would be treated with transarterial embolization.\nAt the time of treatment, general anesthesia was standard care at our institution for AVF embolization. Using total intravenous anesthesia (TIVA, 150 mcg/ml/min propofol) with IONM, we monitored motor evoked potentials (MEPs), somatosenory evoked potentials (SSEPs), electroencephalography (EEG), auditory brainstem response (ABR), VEPs, and ERG signals. Monitoring was done to evaluate for all potential neurophysiologic changes both locally and distant from the site of the procedure due to blood flow changes during embolization. ERG electrodes were placed above the eye and responses were monitored after independent light emitting diode flash stimulation. Baseline ERG recording to flash stimulation yielded a polyphasic response with a 25.8 ms latency and an amplitude of 14 μV []. VEPs were also recorded concurrently with electrodes CZ, OZ, O1, and O2, for comparison. After baseline signals were acquired, the right femoral artery was accessed sterilely. A standard micropuncture access kit, 6F sheath, and 6F MPC Envoy were used to catheterize the left internal carotid artery. Cerebral DSA was performed [Figure –] and then a Marathon microcatheter (eV3/Covidien, Irvine, CA) and Mirage 0.008” microwire (eV3/Covidien, Irvine, CA) were used to selectively catheterize the left ophthalmic artery and superselective DSA was performed to confirm the position of the microcatheter tip within the arterial pedicle of the AVF. DSA showed no retinal blush confirming positioning of the microcatheter distal to the branching point of the central retinal artery from the ophthalmic artery. A total of 3 mg of methohexital sodium (Brevital) was injected into the AVF pedicle without changes in IONM signals. Subsequently, Onyx 18 (ev3/Covidien, Irvine, CA) was used to embolize the arterial pedicle without changes in IONM. However, 10 min later, as the second left ophthalmic pedicle was about to be accessed for potential embolization, we noted a significant change in ERG (10 ms increase in latency and 30% decrease in amplitude) compared with baseline and signals on the right [].\nPostembolization DSA showed a more prominent retinal blush suggesting increased flow through the central retinal artery [Figure –]. With no additional manipulations, the change in ERG signal subsequently returned to baseline within several minutes when blood pressure was decreased from a baseline systolic of approximately 90. A decision was made to stop the procedure after single pedicle occlusion due to a concern for possible retinal hyperemia and damage that may result in retinal damage if we performed additional embolizations. After awakening from general anesthesia, the patient had no deficits in visual acuity or field testing, but did complain of transient pain with eye movement that resolved the next day and worsened with episodes of blood pressure elevation.\nThe treatment was staged to minimize large acute hemodynamic changes in the retina that potentially could cause retinal damage. Staged embolization resulted in angiographic cure of the lesion without complication.