Posterior fossa revascularization by superficial temporal artery (STA)--superior cerebellar artery (SCA) anastomosis

Anatomic variations of the superficial temporal artery

The superficial temporal artery (STA) is a terminal branch of the external carotid artery. It is commonly described as coursing posterior to the mandibular condyle and over the posterior zygomatic root (PZR) and then dividing terminally into parietal and frontal branches. However, possible variations of the main trunk of the STA have seemingly been overlooked. This study retrospectively examined the archived head tomography angiograms of 43 patients to determine the morphology and topography of the STA prior to its terminal bifurcation. In 79% of patients, the STA topography related to the mandibular condyle was bilaterally symmetrical, either retrocondylar (65.1%) or laterocondylar (13.6%). The parietal branch was sometimes absent unilaterally (16.3%) or bilaterally (9.3%). In 2/43 cases, the frontal branch of the STA was unilaterally absent. When both terminal branches were present, the bifurcation was retrocondylar or immediately above the PZR when on the PZR, or the terminal division of the STA was high above the PZR. In 88.4% of the STAs, different patterns of kinking and coiling were documented, including retrocondylar kinks (27.9%), laterocondylar kinks (20.9%), kinks placed on the PZR (81.4%) and variably oriented suprazygomatic kinks (32.6%). Five of the 86 STAs were coiled, one retrocondylar, one laterocondylar, and three other placed on the PZR. Two cases showed unilateral pseudoaneurysms of the STA, one above the PZR and the other on the temporomandibular joint. The STA is surgically important; therefore, the number of anatomical studies of the STA should increase.

Revascularizing the upper basilar circulation with saphenous vein grafts: operative technique and lessons learned

BACKGROUND

The purpose of this study was to report our operative technique and lessons learned using saphenous vein conduits to revascularize the rostral basilar circulation (ie, bypass to the posterior cerebral or superior cerebellar arteries). We also review the evolution of this technique for the treatment of vertebrobasilar insufficiency (VBI) and complex posterior fossa aneurysms.

METHODS

Data were collected retrospectively for 8 consecutive patients undergoing rostral basilar circulation saphenous vein bypass grafts at our institution between 1989 and 2004 for the treatment of VBI or in conjunction with Hunterian ligation of complex posterior circulation aneurysms. The indications for treatment, pre- and postoperative neurologic status, angiographic results, operative complications, and long-term clinical outcomes were analyzed for each patient.

RESULTS

With clinical and angiographic follow-up ranging from 3 months to 15 years, 7 of 8 bypasses remained patent, 3 of 3 aneurysms remained obliterated, and 4 of 5 patients with VBI experienced resolution of their preoperative symptoms. There were no surgery-related deaths, but 2 patients did experience major neurologic morbidity. The outcomes for the 217 total patients reported in the literature were as follows: 135 excellent (62%), 26 good (12%), 30 poor (14%), and 26 dead (12%).

CONCLUSIONS

Despite the risk of serious neurologic complications with this procedure, when one considers the natural history of untreated patients, saphenous vein revascularization of the rostral basilar circulation remains an acceptable option. Although surgical technique has varied, patient selection criteria, graft patency, and patient outcomes have been relatively constant over the past 25 years.

Microsurgical anatomy of cerebral revascularization. Part II: Posterior circulation

Object. Revascularization is an important component of treatment for complex aneurysms, skull base tumors, and vertebrobasilar ischemia in the posterior circulation. In this study, the authors examined the microsurgical anatomy related to cerebral revascularization in the posterior circulation and demonstrate various procedures for bypass surgery.

Methods. The microsurgical anatomy of cerebral and cerebellar vessels as they relate to revascularization procedure and techniques, including extracranial-to-intracranial bypass grafting, arterial interposition grafting, and side-to-side anastomosis, were examined by performing stepwise dissections in 22 adult cadaveric specimens. The arteries and veins in the specimens were perfused with colored silicone.

Dominant cerebral and cerebellar revascularization procedures in the posterior circulations include superficial temporal artery (STA)—posterior cerebral artery (PCA), STA—superior cerebellar artery (SCA), occipital artery (OA)—anterior inferior cerebellar artery, OA—posterior inferior cerebellar artery (PICA), and PICA—PICA anastomoses. These procedures are effective in relatively small but critical areas including the brainstem and cerebellum. For revascularization of larger areas a saphenous vein graft is used to create a bypass between the PCA and the external carotid artery. Surgical procedures are generally difficult to perform in deep and narrow operative spaces near critical vital structures.

Conclusions. Although a clear guideline for cerebral revascularization procedures has not yet been established, it is important to understand various microsurgical techniques and their related anatomical structures. This will help surgeons consider surgical indications for treatment of patients with vertebrobasilar ischemia caused by aneurysms, tumors, or atherosclerotic diseases in the posterior circulation.

The extracranial-intracranial bypass study: how will the outcome affect us?

Extracranial-intracranial bypass is now a commonly performed procedure in centres with a high level of neurosurgical and vascular expertise. Bypass of surgically inaccessible stenoses or occlusions appears to be a logical technique to prevent future stroke but there is much uncertainty about the clinical indications for surgery and even the natural history of the lesions being bypassed. To answer these questions, the International EC/IC Bypass Study was set up in 1977 with relatively broad entry criteria. The data will be analysed in June 1985 and if the results support the use of bypass as a means of preventing subsequent stroke, the procedure should become firmly established. However, if the results are negative, or inconclusive, rather than discard the procedure, subsets of higher risk patients should be sought, in particular using newer methods of assessing cerebral perfusion and metabolism.

Ophthalmopneumoplethysmography (OPG-Gee) without and with bypass-compression for quantification of hemodynamic significance of superficial temporal artery-middle cerebral artery (STA-MCA) anastomosis

The Extracranial-Intracranial (EC/IC) Bypass Procedure is a new method in order to try to increase the Intracranial Perfusion Pressure (ICPP). Postoperative patency of the bypass can be shown by means of Seldinger angiography. By this method no information however is obtained on the hemodynamic function of the bypass. OPG-Gee measures the Ophthalmic Artery Pressure (OAP) which is related to the ICPP. In this study OPG-Gee is performed without and subsequently with compression of the bypass. Quantification of the hemodynamic significance of the bypass is obtained by measuring the pressure decay in the ophthalmic arteries during this procedure. The Rest Pressure Difference (RPD), i.e. the pressure difference between the two ophthalmic arteries without bypass compression is measured. By subtracting the RPD from the BCD the remaining pressure is called the Net Bypass Pressure (NBP), i.e. the pressure difference, which the EC/IC bypass contributes to the ICPP. If, however, at constant systemic arterial blood pressure (SABP) the OAP drops during bypass compression on both sides, we hypothesize that the NBP is the sum of both drops, because, as a result of the interhemispheric steal mechanism, the less perfused hemisphere steals from the better perfused hemisphere. In a group of 40 patients OPG-Gee without and subsequently with bypass compression was applied. Twenty two of 40 OPG-Gee's showed NBP's of 4 mm of mercury or more (55%). In the group of 29 patients with unilateral internal carotid artery occlusion in 21 patients (72%) an NBP of 4 mm of mercury or more was found (mean of 13 mm of mercury).(ABSTRACT TRUNCATED AT 250 WORDS)