Fig. 1.2–13a-d A 72-year-old patient with right-sided occlusion of the main trunk of the middle cerebral artery (a) and acute left-sided hemiparesis. The thrombus was passed with a microcatheter (b) and introduction of a Solitaire® stent (c; arrow: distal stent marker), with revascularization with the opened stent lumen. Removal of the stent and successful thrombus extraction from the main trunk of the middle cerebral artery (d). It was not possible in this case to reopen an M2 branch, despite supplementary rt-PA administration and attempts at mechanical thrombolysis.
If recanalization is successful and an underlying stenosis is identified (Fig. 1.2-12), it is beneficial due to the high rate of recurrent occlusion to treat the stenosis during the same session (with PTA alone or in combination with a stent). Unfortunately, the clinical outcome for the affected patients does not depend only on the recanalization of the vessels. The duration and location of the vascular occlusion, the collateral blood supply, the side of the affected brain area that has already suffered infarction, and concomitant diseases that the patient may have also play an important role.
Fig. 1.2–15a-c A 52-year-old patient with high-grade stenosis of the vertebral artery on the right side (a, arrow), with recurrent TIAs and occlusion of the vertebral artery on the left. A Pharos® stent was placed at the level of the stenoses, with an inflated balloon (b). Normalization of the vascular caliber following complication-free stenting (c).
In rare cases when there is persistent intermittent perfusion, recanalization treatment for non-acute, chronic vascular occlusion is indicated.
1.2.5.3 Surgical treatment
Surgical treatment for stenotic and occlusive processes in the region of the extracranial and intracranial circulation of the arteries supplying the brain represents a complementary strategy for preventing ischemia-related neurological deficits. In this approach, a further critical underperfusion event in circulation regions that are at risk for ischemia is avoided by carrying out surgical improvement in the exhausted cerebral collateral supply. This strategy is based on the results of studies in which symptomatic patients with signs of inadequate cerebral collateral supply—i.e., hemodynamic insufficiency or exhausted cerebral perfusion reserve—had a markedly higher annual risk of stroke, at 18–46%, in comparison with patients with an intact collateral supply. Patient selection—i.e., the choice of which patients should undergo targeted revascularization—therefore focuses on assessing what is known as the cerebral perfusion reserve. This can be measured using various functional examinations of regional cerebral blood flow (rCBF).
Determining cerebral perfusion reserve
This is based on carrying out paired examinations of the rCBF, with a baseline measurement being carried out in resting conditions. Following a vasodilatory stimulus—e.g., inhalation of carbon dioxide or administration of acetazolamide (15 mg/kg body weight i.v.)—the rCBF is measured again. After appropriate evaluation and application of various calculation algorithms, the perfusion reserve (cerebrovascular reserve capacity, CVRC, expressed as a percentage; also known as the vasomotor reserve) is calculated. For direct measurements of rCBF, methods that can be used include PET, stable Xe-CT, and quantitative SPECT; transcranial Doppler (TCD) ultrasonography only allows indirect estimates.
In physiological conditions, rCBF stimulation can be expected to produce at least a 30% increase in rCBF (CVRC > 30%—i.e., normal). Depending on the extent of hemodynamic restriction, there is then a reduction in reactive vasodilation, so that restricted CVRC is described as being present at a CVRC < 30%. At values < 10%, CVRC is regarded as having been eliminated. When there is a paradoxical reduction in rCBF (CVRC < –5%)—i.e., maximum vasodilation before stimulation and consequent nonreaction of the resistance vessels—it is assumed that an intracranial steal phenomenon is present. This is the most severe grade of hemodynamic impairment and is associated with the highest risk of secondary ischemia (Fig. 1.2-16).
Indications for revascularization
The following criteria generally arise:
With regard to the underlying pathology, there is considerable variability in the pathogenesis. In most cases, the patients have localized or systemic atherosclerosis. In a far smaller proportion of the patients, there is an indication for surgery due to inadequate collateral supply after carotid dissection or progressive tumor growth with resulting constriction or occlusion of the internal carotid artery, mostly in the area of the skull base. Patients with moyamoya disease or moyamoya syndrome represent a special case, which is discussed separately below.
Surgical technique
The aim of the surgical procedure is to normalize the CVRC and thus to “restore” physiological perfusion conditions. The technique used is a standard extracranial–intracranial (EC/IC) bypass. A donor vessel in an extracranial site, usually the superficial temporal artery (STA), is anastomosed with a cortically located branch of the middle cerebral artery (MCA) in the area of the lateral sulcus (sylvian fissure). The procedure is carried out with the patient under general anesthesia, with endotracheal intubation and neuroprotective measures to prevent ischemic complications. After preparation of the donor vessel (the STA), a craniotomy with a diameter of approximately 3 cm is carried out in the area of a defined target point over the lateral sulcus. After opening of the dura mater and exposure of a suitable recipient vessel (the middle cerebral artery in the M2/M3 segment), the standard bypass is placed using an end-to-side technique with 10–12 interrupted sutures (Fig. 1.2-17). The patency of the bypass that has been created can usually be immediately documented intraoperatively using indocyanine green (ICG) video angiography. Thanks to improved perioperative treatment, more sophisticated surgical techniques, and the ability to check the success of the procedure immediately, it is now possible to carry out this procedure with only minor surgical morbidity (< 5%). The operation is only carried out after adequate inhibition of platelet aggregation (100 or 325 mg ASA/d p.o.). Among other things, this makes it possible to achieve a bypass patency of > 98%. Platelet aggregation inhibition starts before the operation and continues on a lifelong basis.
Fig. 1.2–16a, b A standard extracranial–intracranial (EC/IC) bypass in a patient with atherosclerotic occlusion of the right internal carotid artery. (a) Conventional angiography reveals insufficient collateral supply to the right hemisphere. Angiographic demonstration of the STA-MCA bypass using the right superficial temporal artery (STA), which was anastomosed with a distal branch of the middle cerebral artery (MCA). (b) Anteroposterior view.
In addition, selective DSA and