13.1 History and Initial Description

The first description of “moyamoya” disease was by Suzuki and Takaku in 1969. ¹ Three years later, professor Yasargil performed the first surgical intervention for moyamoya with a superficial temporal artery (STA) to middle cerebral artery (MCA) bypass, ² marking the beginning of an evolution in the surgical treatment of the disease. Over the next several decades and into the 21st century, novel surgical strategies have been developed to treat moyamoya disease, and operative techniques have been continually refined. Currently, various operations for both direct and indirect bypass are described to augment blood flow to multiple vascular territories, including the anterior cerebral artery, MCA, and posterior cerebral artery territories. ³

While double-barrel bypass techniques with both the parietal and frontal STA branches have been described, ⁴ the single-vessel double anastomosis (SVDA) technique is a novel strategy that involves utilizing one donor branch for both a side-to-side, and end-to-side anastomosis, provided the donor artery has sufficient flow to supply multiple bypasses. This technique can be an important addition to the bypass armamentarium in selected patients with moyamoya disease, particularly when a single anastomosis is unlikely to supply sufficient flow to multiple ischemic territories, or in cases where there is mismatch between the available flow from the donor graft exceeding the sink capacity of a single recipient bed.

13.2 Indications

Potential candidates for flow augmentation bypass surgery include patients with symptomatic moyamoya disease with poor cerebrovascular reserve as diagnosed on preoperative studies. We prefer to use a vasodilatory challenge paired with imaging studies to assess cerebrovascular reserve and identify areas at risk with impaired autoregulation stemming from a chronic oligemic state. Vasodilatory challenge normally causes a resultant increase in cerebral blood flow, though in instances of hemodynamic compromise, this response will be either dampened or absent in an impaired vascular territory compared to the normal circulation. ⁵ The studies we utilize include quantitative MRA with use of Noninvasive Optimal Vessel Analysis (NOVA) software, with a Diamox challenge, and functional MRI (regional and global blood oxygen level dependent [BOLD] imaging) with CO₂ challenge. Adequate donor and recipient vessels should be available as noted on digital subtraction angiography. The SVDA bypass configuration, in particular, can be selected as an option during preoperative work up if only a single robust usable STA branch is noted on the angiogram and more than one territory requires flow augmentation (such as with superior and inferior MCA division territories). On the other hand, the decision to proceed with SVDA bypass configuration may be taken intraoperatively based on flow measurements of potential donor and recipient vessels. If the cut flow (i.e., free-flowing carrying capacity) of the STA donor vessel is substantial enough to augment two vascular beds, an initial side-to-side anastomosis is performed. The cut-flow index (CFI) is then measured and calculated; if CFI ≤ 0.5, the second anastomosis is completed in an attempt to get the CFI closer to 1, therefore maximizing the graft potential and minimizing type 2c error and bypass failure. ^{6 ,​ 7}

13.3 Key Principles

Once the vascular territories in need of flow augmentation are identified based on patient symptoms (including left vs. right in bilateral disease), imaging findings, and cerebrovascular reserve testing, the skin incision and craniotomy must be carefully planned. Excessive supragaleal dissection and devascularization of the scalp can be spared if only a single branch of the STA is needed. The skin incision is tailored according to the targeted STA branch. If the parietal branch is being dissected, the skin incision will be made following its path; it can then be reflected anteriorly, distal to the superior temporal line, if a larger skin flap is needed. If the frontal branch is harvested, the incision is made to accommodate for an adequate size craniotomy while minimizing the amount of skin reflected anteriorly. The frontal STA will then be dissected from the underside of the skin flap through the galea. When performing the craniotomy and opening the dura, great care should be exercised in preserving the middle meningeal artery (MMA), as it may already provide critical extracranial-to-intracranial (EC-IC) collaterals, as often seen on preoperative angiography. Various donor/recipient vessels should be identified and different direct bypass configurations planned and selected; the surgeon should be ready to adapt and reconfigure the surgical plan based on intraoperative flow measurements. Flow-assisted surgical technique (FAST) is utilized, ⁷ which involves the following: performing flow measurement for the STA cut flow; calculating CFI to predict bypass patency rate ⁶ ; optimizing type 2c error (further described in Chapter 13.4.4); optimizing CFI at 1 by performing more than one anastomosis if needed; maximizing donor capacity.

13.4 SWOT Analysis

13.5 Contraindications

Contraindications to the SVDA technique encompass the usual contraindications to bypass for moyamoya in general, including preserved hemodynamic reserve, poor quality donor vessels, and poor quality recipient vessels. Inadequate vessel length or orientation may also prevent a successful SVDA. Finally, unless the cut flow from the single STA branch is sufficient to supply two separate vascular territories, an alternative technique (double barrel, for example) must be employed.