STA-MCA Microanastomosis: Surgical Technique

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8 STA-MCA Microanastomosis

Surgical Technique

Introduction

The purpose of extracranial to intracranial bypass is always to improve the cerebral blood flow (CBF) by diverting blood flow from the extracranial carotid artery circulation to the intracranial cerebral circulation. There are two main indications for cerebral revascularization procedures: (1) flow augmentation to increase CBF in patients with chronic compromised CBF (chronic cerebral ischemia), and (2) flow preservation to maintain CBF in patients undergoing acute vessel sacrifice (complex aneurysms, skull base tumors). Revascularization procedures can be divided into direct (connecting the donor and recipient vessel directly by microanastomosis) and indirect techniques (laying vascularized tissue in contact with the brain to develop delayed collateralization).

The first successful direct extracranial-intracranial (EC-IC) bypass surgery was performed by Yasargil in 1967.1 Since then, many operative techniques for direct cerebral revascularization have been described (see chapters 7 through 14). The most commonly used EC-IC procedure to revascularize the anterior circulation is the superficial temporay artery (STA)–middle cerebral artery (MCA) bypass between one branch of the STA and a cortical MCA branch (M4). It has the advantage of being a safe, simple, and readily available technique, and the disadvantage of supplying low flow rates. In this chapter we will describe the technical aspects of the STA-MCA bypass as well as the pitfalls and lessons learned by the authors based on their longstanding experience.

Perioperative considerations and surgical technique

The preoperative as well as the postoperative period and special anesthetic considerations are important general steps of the STA-MCA procedures. The surgical technique of the STA-MCA bypass can be divided into four fundamental steps:

Surgical Technique

Preparation of the STA

The patient is placed supine and the head is fixed in a three-point Mayfield fixation frame. The head should be elevated above the heart, turned to the contralateral side, keeping the operative field horizontal to the floor. Depending on the suppleness of the cervical spine, a shoulder roll may or may not be required.

The STA and its branches are mapped with a Doppler ultrasound probe and serve as a guideline for the skin incision (Figure 8–1). Using the operative microscope, a linear skin incision is made directly over the course of the parietal branch of the STA all the way to the zygoma and an 8-cm length of the STA is dissected out. In the event that the frontal branch of the STA is to be used, a curvilinear frontotemporal skin flap behind the hairline allows for a clean dissection of the frontal branch from the underside of the scalp flap. This can be tedious since the dissection from under the flap may require additional skin retraction and dissection through the fat plane.

The STA is then dissected out from the galeal tissue, ensuring that a small cuff (2 to 3 mm) of soft tissue surrounding it remains. Bipolar electrocoagulation of the arterial side branches is performed at a distance of several millimeters to avoid thermal injury to the STA. The isolated STA must be long enough so that no traction occurs during the bypass. The distal end of the artery can then be clipped and divided after temporary clamping at the proximal end, or left intact until after the craniotomy and just prior to the anastomosis (Figure 8–2

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