How to: Positioning for Middle Cranial Fossa Repair of Superior Semicircular Canal Dehiscence

by Nicholas S. Andresen, MD, Pavan S. Krishnan, BA, Brian M. Lin, MD, Eric Formeister, MD, and John P. Carey, MD •

INTRODUCTION

Superior semicircular canal dehiscence syndrome (SCDS) is characterized by sound- and pressure-induced vertigo that is associated with dehiscence of the temporal bone over the superior semicircular canal (Arch Otolaryngol Head Neck Surg. 1998;124:249–258). SCDS may be surgically treated with plugging or resurfacing of the superior semicircular canal dehiscence (SCD) via a middle cranial fossa (MCF) or transmastoid approach (Curr Opin Otolaryngol Head Neck Surg. 2020;28:340–345; Laryngoscope. 2016;126:1218–1224). The MCF approach for SCD repair is traditionally performed with the patient in the supine position.

In the supine position, the patient’s head is turned to the contralateral side and secured with surgical pins, placed on a horseshoe head holder, or supported on a flat head plate on the bed. The park bench position involves placing the patient on their side and provides for further head rotation. However, the park bench position requires extensive manipulation of the patient, which is time-consuming, and increases the risk of endotracheal tube dislodgement and shoulder or arm injury (J Neurosurg Anesthesiol. 2011;23:264; Br J Neurosurg. 2007;21:522–524). Moreover, the trajectory provided by the park bench position better serves a retro-sigmoid, posterior fossa approach. Furthermore, the geometry of the superior canal does not require such a severe head turn towards the floor. Instead, a lateral approach to the arc of the superior canal requires 70° to 90° of head rotation: 45° to account for the angle of the canal from the sagittal plane and an additional 20° to 40° to allow the surgeon to access the arc of the canal from its lateral aspect. This amount of head rotation can only be achieved in a minority of patients with their bodies in the supine position. Even then, such a head-on-neck position risks compression of the ipsilateral jugular vein, which could lead to excess intracranial pressure.

Figure 1. After placement of the surgical navigation post, the patient’s head is turned to the contralateral side and the incision is marked. Auditory brainstem neuromonitoring probes are then placed.

Here we present a novel method of positioning the patient for SCD repair that allows for optimal rotation of the head in a semi-supine position, requires less set-up and patient manipulation than the park bench position, and does not require the use of surgical pins. The proposed method also allows the surgeon to maintain an ergonomically ideal posture during microdissection, avoiding tilting of the surgeon’s head on the torso.

METHOD

A review of patients who were scheduled to undergo SCD surgery via a MCF approach by the senior author was performed. A case was selected to demonstrate the novel positioning during SCD surgery using an MCF approach.

Technique

The patient is brought to the operating room and general anesthesia is induced. Following endotracheal intubation, the bed is rotated 180° away from anesthesia and the head is marked for placement of the surgical navigation post on the side of the patient’s head closest to the navigation tower. The scalp is prepped in a sterile fashion, and the navigation post is placed. The head is then placed on a horseshoe headrest, and the head is turned to the contralateral side. The skin incision is marked, the patient is injected with local anesthesia, and auditory brainstem neuromonitoring probes are placed (Figure 1). Facial nerve monitors are placed.

The patient is initially positioned supine on the operating table with a drawsheet beneath them. The drawsheet must be of sufficient length on either side to wrap the patient with their arms at their sides. The upper edge of the drawsheet reaches the axillae, and the torso is positioned such that the rib cage is aligned with the contralateral edge of the bed; this accounts for any tendency of the body to shift when the operating table is tilted in that direction. Padding is placed across the patient’s chest, and the patient is secured to the operating table with a circumferential wrap using three-inch silk tape around the bed and the chest. The arms are not taped within this circumferential chest wrap because doing so might increase the risk of brachial plexus injury from compression should the torso shift toward the arm with bed rotation. Instead, the arms are first wrapped in foam or gel padding at the levels of the wrists and elbows and then cradled in place by tying the drawsheet across the patient’s body at the level of their chest and hips. The arms should be positioned slightly anterior to the body when secured with the bedsheet. This avoids both brachial plexus injury from scapular retraction and hyperextension of the elbows. Foam pads should be placed beneath the knots used to tie the bedsheet. Additional safety straps are placed across the hips and legs to secure the patient to the bed.

The horseshoe headrest is positioned so that the patient’s head is turned as far as possible to the contralateral side without placing undue stress on the patient’s neck.

The operating table is then tilted towards the contralateral side to bring the patient’s temporal cranium to a plane parallel to the operating room floor (Figure 2). The surgical site is then prepped and draped. This positioning technique is further demonstrated in the supplemental video.

A retrospective chart review was performed for the last 100 individuals who underwent MCF SCD repair by the senior author and were positioned using this technique to evaluate its efficacy. All cases occurred between the years 2019–2022. Medical records were reviewed for the incidence of intra-operative endotracheal tube dislodgement, adequacy of surgical exposure to complete SCD repair without patient repositioning, and post-operative patient neck or shoulder discomfort.

RESULTS

Assessment of Positioning Technique.

One hundred patients were identified who underwent MCF SCD repair by the senior author between 2019 and 2022 and were positioned using the technique described above. There were no episodes of intraoperative endotracheal tube dislodgement and adequate surgical exposure was achieved in every case without patient repositioning. One individual (38-year-old male) noted postoperative shoulder soreness on the night of surgery. This patient was examined by the orthopedics service and was not found to have any fracture or neurological deficit. His shoulder soreness improved significantly before discharge from the hospital on postoperative day three and he remained happy with his surgical outcome. No other patients reported neck or shoulder soreness post-operatively.