The cerebrovascular steno-occlusive disease can cause acute cerebral infarction or transient ischemic accident (TIA) symptoms. An unstable TIA can originate from decreased cerebral perfusion; therefore, immediate and adequate blood supply is the most crucial consideration in bypass surgery. STA-MCA bypass is a relatively simple and efficient surgical modality, especially for cerebrovascular occlusive diseases with a high patency rate during a short period. However, the STA is inaccessible for bypass in cases of previous operations, injuries, or atrophy. In this condition, interposition graft surgery is considered. The graft technique is more complex and requires additional anastomosis, increasing operation difficulty and requiring more time. However, there are disadvantages to this technique, such as donor site complications and size discrepancy-related graft failure. Moreover, there is a hyperperfusion syndrome risk if the donor artery is large.
Direct OA bypass can be an alternative to the interposition graft with the advantage of arterial graft use. In cases 1 and 2 presented here, the OA was selected as an alternative because the STA was too thin. Direct OA-MCA bypass for ischemic stroke has rarely been reported in literature[4-7]. OA is a frequently used donor artery for trapping and bypassing aneurysm surgeries arising from posterior circulation. Meanwhile, bypass from the OA to the MCA is not commonly performed because of its technical difficulties. The OA is more onerous to harvest than the STA because it passes through several tortuous layers.
Successful OA-MCA bypass techniques
In the three-quarter position, the retrosigmoid area was at the top, and the vertex was slightly raised to reduce venous pressure (Figure 3A). After marking the OA path, as confirmed through angiography and fingertip palpation, a microscopy-guided incision was made on the OA course (Figure 3A). The artery was located, and the soft tissue was bluntly dissected. Small OA branches were identified and cut after meticulous cauterization. The proximal part was secured through dissection to where the OA penetrated the splenius capitis muscle. The large branch in the main artery’s subgaleal portion was likely to be used for a second anastomosis and could be cleaned of the donor artery to ensure its preservation to the greatest extent. The splenius capitis muscle was incised along the OA. Free space was secured by dissecting and retracting the muscle, creating a vascular groove. The descending branch that supplies blood flow to the suboccipital muscle was preserved as much as possible; however, if OA’s full length was not long enough, it was selectively cut after ligation. A length sufficient for MCA bypass is approximately 7 cm above the proximal stump, which is just below the superior nuchal line (Figure 3B). However, this varies depending on OA functionality and condition.
Figure 3 Occipital artery-middle cerebral artery bypass surgical position and incision.
A: In the three-quarter position, the retrosigmoid area was at the top, and the vertex was slightly raised. The occipital artery (OA) course was confirmed through angiography with fingertip palpating. An incision was created consecutively at the craniotomy site for the recipient artery; B: The OA’s main artery had a very tortuous course (black arrows); therefore, the soft tissue was dissected along the bend to secure the stretched curve’s full length to the recipient site, at least 7 cm; C and D: To prevent donor artery compression in the supine position, a route between the craniotomy site and OA’s proximal part was cut to create a sough (black arrows).
The posterior Sylvian fissure area should be exposed to access the donor artery for MCA bypass. The incision was extended according to the recipient’s target craniotomy location. To achieve an MCA bypass, the skull was exposed enough to incise the skin by anteriorly turning it vertically along the superior temporal line. If the OA was bent superomedially, a separate incision was conducted in the temporal region for craniotomy of the recipient artery. Following this, the OA can be passed through the subcutaneous tunnel for an OA-MCA bypass. To prevent donor artery compression in the supine position, a route between the craniotomy site and the OA’s proximal part was cut to create a sough (Figure 3C and D). Particular caution was exercised on the secured OA when making the furrow. Small fabrics were not typically placed around the drill. An end-to-side anastomosis was performed with nylon 10-0 in the recipient artery, such as the angular artery. As the OA had a tortuous path, the surgeon did not point the anastomotic end in a direction that twisted the blood vessel. The recipient artery was a peripheral artery and thinner than the M4 used for STA-MCA bypass. Therefore, the arteriotomy must be slightly longer than the STA-MCA bypass to match the anastomosis length accurately. With these points in mind, the authors successfully performed a less invasive bypass surgery.
A particular postoperative wound necrosis risk is possible due to insufficient collateral superficial blood circulation if an ipsilateral bypass surgery has been performed previously. In patients who have undergone the indirect bypass alone, additional surgery might worsen the overlying scalp’s blood circulation, resulting in ischemia in the existing bypass area. Therefore, accurate confirmation is necessary for the donor artery course based on preoperative imaging tests, including angiography, and to minimize collateral blood vessel damage during skin incision and dissection.
The recipient artery choice is controversial. Bypassing at the best location is vital for improving the patient's symptoms; however, it might be preferred to select a nearby artery considering the OA’s available length. Hirano et al. have proposed two incision methods to approach the recipient artery regarding the OA’s travel direction and distance to the recipient artery: an extension of the OA incision and an additional incision, respectively. The recipient artery was accessed through a single incision in the cases presented here. When an OA of sufficient length is harvested, bypass surgery can be performed less invasively without additional incision. This is also advantageous from a cosmetic point of view.