Superficial Temporal Artery: Middle Cerebral Artery Bypass, Our Series of 20 Cases, Surgical Technique and Indications with Illustrative Cases

Evaluation of Preoperative Low-flow Areas in STA-MCA Bypass Surgery Using Vascular Fusion Map Image

BACKGROUND

The superficial temporal artery-middle cerebral artery (STA-MCA) bypass surgery requires an anastomosis of the STA to an MCA with diminished blood flow. However, identifying the precise location of the MCA with reduced flow preoperatively is challenging as it often remains nonvisualized. To address this issue, we developed a novel technique, the area target bypass (ATB) method, to infer the location of the responsible vessel for low-flow areas.

OBJECTIVE

The cornerstone of the ATB method lies in the utilization of the vascular fusion map (VFM). The VFM integrates 3D perfusion and 3D vascular images, enabling simultaneous evaluation of cerebral surface vessels and regions with reduced blood flow. This study aimed to assess the efficacy of the STA-MCA bypass surgery adopting the ATB method.

METHODS

Between August 2022 and March 2023, we conducted eight STA-MCA bypass surgeries using the ATB method. For each case, the VFM was generated using the MTT and DLY parameters, and blood flow improvement was evaluated based on the VFM score, determined by an average score from seven experts.

RESULTS

In all cases, the target vessel was identified either preoperatively or during craniotomy, with postoperative patency of the STA-MCA bypass confirmed. Out of the eight cases, seven demonstrated improved blood flow with a VFM score exceeding 1. No complications were reported.

CONCLUSION

The introduction of the ATB method has proven its potential in accurately pinpointing optimal anastomosis sites.

Constructing an Individualized Middle Cerebral Artery Model Using 3D Printing and Hydrogel for Bypass Training

The importance and complexity of cerebral bypass surgery (CBS) highlight the necessity for intense and dedicated training. Several available training models are yet to satisfy this need. In this technical note, we share the steps to construct a digital imaging and communications in medicine (DICOM)-based middle cerebral artery (MCA) model that is anatomically accurate, resembles handling properties of living tissue, and enables trainers to observe the cerebrovascular anatomy, improve and maintain microsurgical dexterity, and train in the essential steps of CBS. The internal and external molds were created from the geometry of DICOM-based MCA using Fusion 360 software (Autodesk, San Rafael, USA). They were then three-dimension (3D) printed using a polylactic acid filament. The 15% w/v solution of polyvinyl alcohol (PVA) was prepared and injected between the molds. Using five freeze-thaw cycles the solution was converted to tissue-mimicking cryo-gel. The model was then placed in a chloroform bath until the internal mold dissolved. To evaluate the accuracy of the MCA model, selected characteristics were measured and compared with the MCA mesh. The DICOM-based MCA model was produced using 3D printing that was available in the lab and the overall cost was less than $5 per model. The external mold required six and a half hours to be 3D printed, while the internal mold only required 23 minutes. Overall, the time required to 3D print the DICOM-based MCA model was just short of seven hours. The greatest statistically significant difference between the virtual MCA model and the DICOM-based MCA model was found in the length of the pre-bifurcation part of the M1 segment and the total length of the superior bifurcation trunk of M1 and superior branch of M2. The smallest statistically significant difference was found at the diameter of the inferior post-bifurcation trunk of the M1 segment and the diameter at the origin of the artery. This technical report aims to show the construction of a CBS training system involving the DICOM-based MCA model that demonstrates the shape of the vascular tree, resembles the handling/suturing properties of living tissue, and helps set up a homemade training station. We believe that our DICOM-based MCA model can serve as a valuable resource for CBS training throughout the world due to its cost-effectiveness and straightforward construction steps. Moreover, once the DICOM-based MCA model is used with our training station, it may offer an option for trainers to gain and maintain CBS skills despite limitations on time, cost, and space. This work was presented in February 2019 at the American Association of Neurological Surgeons/Congress of Neurological Surgeons (AANS/CNS) Cerebrovascular Section Annual Meeting held in Honolulu, Hawaii.

Superficial Temporal Artery to Middle Cerebral Artery Cranial Bypass for Nonmoyamoya Steno-Occlusive Disease in Patients Who Failed Optimal Medical Treatment: A Case Series

BACKGROUND

In the post-Carotid Occlusion Surgery Study (COSS) era, multiple reviews suggested subset groups of patients as potential candidates for superficial temporal artery to middle cerebral artery (STA-MCA) bypass. Among them are patients with recurrent strokes despite optimal medical therapy. There is a paucity of data on the outcome of bypass in these specific patients.

OBJECTIVE

To examine the safety and efficacy of direct STA-MCA bypass in patients with nonmoyamoya, symptomatic steno-occlusive disease with impaired distal perfusion, who failed optimal medical management or endovascular treatment.

METHODS

A retrospective review was performed to identify patients with cerebrovascular steno-occlusive disease who underwent bypass after symptomatic recurrent or rapidly progressive strokes, despite optimal conservative or endovascular treatment.

RESULTS

A total of 8 patients (mean age 60 ± 6 yr) underwent direct or combined direct/indirect STA-MCA bypass between 2016 and 2019. All anastomoses were patent. One bypass carried slow flow. There were no procedure-related permanent deficits. One patient developed seizures which were controlled by medications. A total of 7 out of 8 patients were stable or improved clinically at last follow-up (mean 27.3 ± 13.8 mo) without recurrent strokes. One patient did not recover from their presenting stroke, experienced severe bilateral strokes 4 mo postoperatively, and subsequently expired. Modified Rankin Scale (mRS) improved in 6 patients (75%), remained stable in 1 patient (12.5%), and deteriorated in 1 (12.5%). Good long-term functional outcome was achieved in 5 patients (63%, mRS ≤ 2).

CONCLUSION

Patients with symptomatic, hypoperfused steno-occlusive disease who fail optimal medical or endovascular treatment may benefit from cerebral revascularization. Direct or combined STA-MCA bypass was safe and provided favorable outcomes in this small series.

Long-Term Patency and Final Structure After Superficial Temporal Artery-Middle Cerebral Artery Bypass Surgery: A Retrospective Study

OBJECTIVE

To investigate long-term bypass patency and final structure for patients who underwent superficial temporal artery (STA)-middle cerebral artery (MCA) bypass.

METHODS

This study retrospectively evaluated 20 patients who underwent STA-MCA bypass and had 2-year follow-up with cerebral angiography. Patients were divided into internal carotid artery occlusion (n = 11) and MCA occlusion or stenosis (n = 9) groups, and diagnosis was either arteriosclerotic (n = 14) or nonarteriosclerotic (n = 6) disease. Final bypass formation was examined with cerebral angiography at 2 years postoperatively. Diameters of the STA, middle meningeal artery (MMA), and deep temporal artery (DTA) were measured at preoperative angiography and at 2-year follow-up.

RESULTS

No significant differences in STA, MMA, and DTA diameters were reported between the internal carotid artery versus MCA group. For patients with arteriosclerotic disease, thicker STA diameters were noted on preoperative angiography. For patients with nonarteriosclerotic disease, MMA and DTA dilatation was noted on 2-year follow-up imaging. For patients with arteriosclerotic disease, all direct bypasses were patent at 2 years. For patients with nonarteriosclerotic disease, remarkable angiogenesis was demonstrated.

CONCLUSIONS

Long-term patency of a direct bypass may be correlated with arteriosclerotic or nonarteriosclerotic etiology. An indirect bypass route may develop in patients with nonarteriosclerotic disease; therefore, it is important to create a foundation for an indirect bypass with MMA and DTA preservation during craniotomy. In 2 patients with nonarteriosclerotic disease, STA remained the primary bypass foundation; however, the technique resembled novel angiogenesis after encephaloduroarteriosynangiosis and not direct STA-MCA bypass. Therefore, final bypass structure might be affected by disease etiology.