A 9-year-old girl affected by neurofibromatosis type I presented with multiple transient ischemic attacks (TIAs) consisting either of diplegia of the legs or monoparesis of the left arm, combined with frequent headaches. Neurological examination showed no deficits. Neuroimaging (MRI, MRA and DSA) demonstrated bilateral occlusion of the terminal ICA and the M1 and A1 segments, with bilateral typical compensatory moyamoya vessels. The patient was diagnosed as having MMS. An [¹⁵O]H₂O-positron emission tomography ([¹⁵O]H₂O-PET) scan documented extensive decreased baseline CBF in the right MCA and frontal area as well as severely impaired cerebrovascular reserve (CVR) in almost the entire right hemisphere after the administration of acetazolamide. Moderately decreased baseline CBF was seen in the left hemisphere, especially the frontal area, with well-preserved CVR in the MCA and posterior cerebral artery territory, but decreased frontal CVR (Fig. 1a, c). Based on the symptomatic course of the disease and the hemodynamic insufficiency, surgical revascularization was indicated and aimed at increasing the blood supply to the right MCA and frontal territories.

After general anesthesia, the patient was placed in the supine position with the head mildly extended and rotated 30° to the left in a Mayfield headrest. The first procedure step consisted of a right-sided STA-MCA bypass along with EMS. A linear incision located behind the hairline over the course of the STA was performed, without shaving the hair. The classic technique of an STA-MCA bypass was followed [9]. The parietal branch of the STA was dissected and the small branches arising from the STA were coagulated and cut. The donor vessel was kept intact until the anastomotic procedure was started. The temporal muscle was dissected and cut along the skin incision and a craniotomy was performed along the Sylvian fissure. The dura mater was thereafter carefully opened in a star fashion to maintain the main branches of the middle meningeal artery; dural flaps were reflected over the brain surface underneath the bone window and EDS was obtained by creating contact between the external surface of the dura and the brain surface. Afterwards, the cortex was surveyed for the largest cortical recipient artery. After identification of the most suitable recipient vessel, it was dissected by means of an arachnoid opening. A temporary non-traumatic microvascular clip was placed across the proximal exposed STA. A fish-mouth cut was then executed at the distal STA to increase the donor vessel’s opening diameter. The STA was passed through a small cut performed in the temporal muscle (in order to allow its intracranial entrance, with no risk of compression). A blue dye was put onto the surface of the cutting edges of the donor and recipient vessels to visualize the edges clearly during the anastomotic procedure. Non-traumatic microvascular clips were applied on the recipient vessel and two silicon triangle-shaped background sheets inserted beneath, in order to simplify the construction of the anastomosis. Thereafter, a linear arteriotomy on the cortical recipient vessel was performed. Two 10-0 monofilament sutures were used to anchor the donor and recipient vessel at the toe and the heel of the anastomotic site. The anastomosis was then completed by means of interrupted microsutures to allow eventual anastomosis growth with time. First the distal and then the proximal temporary clips on the cortical MCA recipient artery, and subsequently the clip on the proximal STA were removed. Verification of the bypass patency was performed by Indocyanine Green Videoangiography (performed by using a commercially available surgical microscope, OPMI^® Pentero™, The Carl Zeiss Co., Oberkochen, Germany). Bidirectional flow through the MCA was assessed and all flows were quantified (18 ml/min) using a flow probe (Transonic system, Inc.^© Ithaca, NY, USA). After establishing the bypass, EMS was performed. The previously made burr hole was enlarged to permit the intracranial entrance of the bypass without risk of compression, and the bone was returned to its normal position and secured in place.