9.1 History and Initial Description

Superficial temporal artery (STA) to middle cerebral artery (MCA) nowadays represents an established technique for flow augmentation in chronic cerebral ischemic diseases. Yasargil was the first who described this procedure after technical development of microvascular anastomosis in dogs. He performed the first STA–MCA bypass in a human in 1967 to treat a patient with complete MCA occlusion, ¹ carrying out an end-to-side anastomosis between a distal branch of STA and a cortical branch of MCA near the sylvian fissure. Variations of this procedure have been described, such as end-to-end anastomosis and double-limb STA–MCA grafts, but the original technique is still the most widespread.

One of the first applications in moyamoya disease was reported in 1980, by Holbach and coworkers, on a 41-year-old Libyan woman. ² The authors evaluated the usefulness of direct revascularization through postoperative EEG (electroencephalography), which showed an “increase in the electrical brain activity.” ² The effectiveness of this procedure has been afterward evaluated through flow measurement tools ³ and imaging, such as magnetic resonance (MR) angiography, ⁴ even if angiography provided the clearest evidence in terms of improvement of intracranial circulation following bypass.

The value of STA–MCA bypass in moyamoya disease has been unclear for a long time, due to the scarcity of large series with long-term follow-up and the presence of patients largely treated with indirect revascularization techniques. In 2009, Steinberg and coworkers ⁵ reported a large cohort of patients with moyamoya treated at Stanford University, describing the benefit of direct bypass in terms of prevention of ischemic events and improvement of life quality.

Several studies have subsequently confirmed these findings and at present, STA–MCA bypass is well recognized as a useful treatment approach for moyamoya patients.

9.2 Indications

STA–MCA bypass, compared to indirect revascularization techniques, provides a great advantage of immediately increasing the blood flow in chronic hypoperfused brain. Its protective effect has been demonstrated both for ischemic and hemorrhagic moyamoya disease ⁶ because it implies a double result: improvement of cerebral perfusion and reduction of hemodynamic stress on collateral fragile moyamoya vessels, usually very prone to rupture. Medium term follow-up studies showed that the incidence of both ischemic and hemorrhagic strokes decreases, making STA–MCA bypass a universal indication for moyamoya disease, when technically feasible. The size of the vessels represents, in fact, the most important feature in decision making because a diameter of less than 1 mm makes the anastomosis technically difficult or even impossible. It is therefore deductible that in pediatric patients, indirect revascularization is sometimes the sole practicable surgical option.

Preoperative digital subtraction angiography (DSA) is the gold standard in assessing the caliber of STA; nevertheless, the surgeon must keep in mind that, sometimes, the existent size of parietal and frontal branches observable during surgery is superior to the one expected according to imaging.

9.3 Key Principles

The classic and most widespread technique for STA–MCA bypass consists in performing a direct end-to-side anastomosis of one STA distal branch (parietal or frontal) with a cortical M3 branch, exposed through a small craniotomy ideally targeted on the distal portion of the sylvian fissure. The selection of the most prominent STA branch as well as an appropriate antiplatelet management are milestones for success.

9.4 SWOT Analysis

9.5 Contraindications

Contraindications are few but significant. First, the presence of acute stroke with large restricted signal in diffusion weighted imaging represents a major contraindication; performing the procedure at least 6 weeks after the stroke can be considered safe. Second, it is possible that none of STA branches is suitable as a donor vessel or the artery is absent for different reasons (i.e., previous surgery); in this situation, alternative techniques must be considered. Lastly, the presence of substantial contribution to collateralization from STA needs to be evaluated in each patient prior surgery, weighting risks and benefits of the procedure.

9.6 Special Considerations

9.7 Pitfalls, Risk Assessment, and Complications

STA–MCA bypass carries non-negligible risk of complications. Steinberg and coworkers, in their large cohort, experienced postprocedural hemorrhagic strokes in 1.8% of treated patients, as well as 3.5% of neurological deficits. Schubert et al ⁷ reported an incidence of 8.5% of perioperative ischemic strokes, and a revision rate of 3.1%. General risks (i.e., infections, cerebrospinal fluid leak) are comparable to other neurosurgical procedures.