12.1.2\ Indirect Extracranial-

Intracranial Revascularization

12.1.2.1\ Discussion

Indirect surgical revascularization can be performed as part of complex aneurysm obliteration and moyamoya disease primarily in adults. There are several methods for establishing indirect revascularization, including multiple burr holes, encephaloduromyosynangiosis, and encephaloduroarteriosynangiosis/pial synangiosis, among others.

Creating burr multiple holes (Fig. 12.6) can promote neovascularization to the brain surface. On post-contrast images, enhancement across the burr holes can be appreciated and ADC maps can show increased diffusivity. Depending on the particular technique, favorable results are achieved in nearly 90% of cases. However, in some cases, the delicate anastomoses may not provide sufficient revascularization, and cerebral infarction may result as the underlying disease process ensues.

Encephaloduroarteriomyosynangiosis(EDAMS) consists of creating a linear craniotomy, narrow dural opening, and placing temporalis muscle flaps directly upon the exposed pial surface to stimulate collateral development (Fig. 12.7). The superficial temporal artery and attached flap are then sutured to the dura. Alternatively, encephalomyosynangiosis (EMS) can be performed for increasing both intracranial and extracranial collateral circulation by

inserting the temporal muscle deep to the craniotomy flap directly upon surface of the brain. During the early postoperative period, the swollen muscle can exert mild mass effect upon the underlying brain parenchyma (Fig. 12.8). Postoperative angiography reveals good revascularization in the majority of cases.

Encephaloduroarteriosynangiosis (EDAS)/ pial synangiosis consists of creating a defect in the dura and arachnoid to enable direct suturing of the superficial temporal artery to the pia (Fig. 12.9). Following successful synangiosis, angiography shows progressive reduced flow in the moyamoya vessels and increase in size of the superficial temporal artery.

Angiography is well suited for monitoring the effects of synangiosis. Indeed, the angiographic findings of synangiosis are characteristic and include early filling of the middle cerebral artery branches via ECA injection, enlargement of the superficial temporal artery and middle meningeal artery, and the presence of transpial or transdural collateral vessels. Progression of proximal MCA or ICA stenosis is often apparent despite a successful surgical and clinical outcome, presumably due to diverted blood flow through the ECA circulation. In fact, the lack of MCA or ICA stenosis is associated with a relatively poor outcome. CT and MRI can be used to assess for complications, which include recurrence of ischemic events and chronic subdural hematomas.

Fig. 12.7  Encephaloduromyosynangiosis. The patient has a history of left MCA occlusion as well as right MCA and ACA stenosis. The patient was managed medically but recently developed repeated episodes of transient ischemic attacks to the left hemisphere. Consequently, an onlay external to internal carotid artery bypass with myosynangiosis was performed. Specifically, a direct anastomosis was not feasible due to lack of adequately patent cortical branches. Rather, the superficial temporal artery branch was placed over the brain surface along with its fascial cuff. This was done after multiple openings were made in the arachnoid to allow for percolation of cerebrospinal fluid. In addition, the temporalis muscle flaps were

placed on the exposed brain surface to allow for additional synangiosis. Axial CTA image (a) performed shortly after surgery shows a left temporal microcraniotomy and temporalis muscle flap with a superficial temporal artery branch and fascial cuff (arrow) juxtaposed against the brain surface. Lateral digital subtraction angiography imaged obtained by injection through the left common carotid artery 3 months after surgery (b) demonstrates small collateral vessels (encircled) communicating between the intracranial and extracranial arteries. Axial CTA obtained 9 months after surgery (c) also shows formation of small collateral vessels (encircled) that bridge the temporal lobe cortex and temporalis muscle

Fig. 12.9  Encephaloduroarteriosynangiosis/pial synangiosis. Axial CTA image (a) and coronal (c) contrast-­ enhanced MRA image (b) show the left superficial temporal artery (arrows) passing through the small craniotomy defect

to contact the pial surface of the brain. The prominent left superficial temporal artery (arrow) supplying the pial surface of the brain is also well depicted on the digital subtraction angiogram (c) from an external carotid artery injection

12.1.3\ Intracranial Aneurysm

Wrapping

12.1.3.1\ Discussion

The concept of wrapping aneurysms with strips of muscle tissue was first introduced by Cushing as a treatment of ruptured aneurysms. The temporalis muscle is an accessible source of the necessary tissue. Alternatively, muslin has also been used as a wrapping material. Since the 1980s, the practice of wrapping aneurysms has declined in popularity. Nevertheless, muscle wrapping is still used as a last resort for treatment of aneurysms when endovascular stenting/embolization or surgical clipping is not feasible.

Following aneurysm wrapping surgery, the aneurysm will typically appear about the same size or perhaps slightly smaller, since the main goal of the procedure is to prevent further expansion. Although the muscle wrap itself is often inconspicuous, it should not be confused with tumor or other abnormalities, such as hemorrhage, on imaging (Fig. 12.10). However, the wrap can resorb and allow aneurysm expansion and bleeding. Other complications include infection or foreign body reaction, if synthetic materials are used. Thus, the role of imaging following aneurysm wrapping is to evaluate for integrity of the wrap, aneurysm expansion or hemorrhage, and abscess or muslinoma formation.

Fig. 12.10  Muscle wrap. The patient had a history of a growing left P1 segment aneurysm. Although aneurysm clipping was planned, muscle wrap was instead performed because clipping posed significant risk of occlusion of the thalamic perforator or constriction of the left P1 segment. Temporalis muscle was harvested. Preoperative axial CT (a) and CTA (b) images demonstrate an aneurysm arising from the posterosuperior aspect of the left P1 segment

(encircled). Postoperative axial CT (c) and CTA (d) images show left temporal craniotomy and interval placement of the muscle wrap, which appears as soft tissue attenuation material surrounding the aneurysm and partially filling the left quadrigeminal plate cistern (arrows). The aneurysm is slightly less prominent than before surgery