Foramen Magnum Decompression of Chiari Malformation Using Minimally Invasive Tubular Retractors

43 Foramen Magnum Decompression of Chiari Malformation Using Minimally Invasive Tubular Retractors

Renée Kennedy, Mohammed Aref, Jetan Badhiwala, Brian Vinh, Saleh Almenawer, and Kesava (Kesh) Reddy

43.1 Clinical Case Example

A 50-year-old male presented with a 6-month history of occipital headaches and paresthesias affecting both hands. The headache was worsened by the Valsalva maneuver and had not been relieved by any medical therapy. CT demonstrated a 12-mm cerebellar tonsillar descent below the foramen magnum (Fig. 43.1). MRI of the brain and spine suggested impaired flow of CSF across the foramen magnum secondary to tonsillar herniation (Fig. 43.2), with no evidence of syringomyelia (Video 43.1).

Fig. 43.1 Head CT demonstrating cerebellar tonsillar descent.

Fig. 43.2 MRI of the brain confirming the diagnosis of Chiari I malformation.

Fig. 43.3 Fluoroscopic image demonstrating insertion of a K-wire onto the inferior aspect of the occipital bone.

43.2 Preoperative Plan

• The patient was selected to undergo foramen magnum decompression through a minimally invasive technique using the operative microscope and METRx (minimal exposure tubular retractor) tubular retractor system (Medtronic, Memphis, TN).

• Under general anesthesia and endotracheal intubation, the patient was positioned in the prone position with the head in a three-pin Mayfield frame and the cervical spine slightly flexed. Care was taken to ensure that ventilation was not compromised and that the endotracheal tube was accessible to the anesthesiologist.

• The hair was appropriately shaved, and the skin from the occipital protuberance to the spinous process of C2 was prepped and draped in the usual sterile fashion.

• Somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) were monitored throughout the procedure.

43.3 Surgical Procedure

• A small midline incision was made over the suboccipital region through the skin, subcutaneous tissue, and fascia.

• Under fluoroscopic guidance, a K-wire was introduced above the foramen magnum onto the inferior aspect of the occipital bone, with care taken to avoid entry into the occiput–C1 junction (Fig. 43.3). Once appropriate K-wire position was confirmed on fluoroscopic views, the skin and fascia incision was extended to accommodate the first tubular dilator. The first dilator was placed in position, and the K-wire was removed.

• Tubular dilators of progressively increasing diameter were sequentially placed to a depth appropriate for the thickness of the underlying tissue and muscle (Fig. 43.4). The goal was to gradually distract the soft tissues to provide a final viewing diameter of 22 mm prior to opening the two leaves of the Quadrant system.