Surgical Treatment of Moyamoya Disease in Adults

Introduction

Moyamoya disease is a chronic, occlusive cerebrovascular disease with unknown etiology characterized by steno-occlusive changes at the terminal portion of the internal carotid artery (ICA) and an abnormal vascular network at the base of the brain. These vessels are called “moyamoya vessels” because the angiographic appearance of these vessels resembles the “cloud” or “puff” of cigarette smoke, which is described as “moya-moya” in the Japanese language; also, “moya-moya” is the Japanese word to describe a hazy appearance or an unclear idea about something.

In the 1950s, leading Japanese neurosurgeons began to notice a new clinical entity that came to be called moyamoya disease. Since its etiology was unknown, it was named in various ways. Takeuchi and Shimizu described it as a hypoplasia of bilateral internal carotid arteries. Later, Suzuki and Takaku described in detail the angiographic appearance and development of this disease,1 and gave it the name moyamoya disease. Kudo named it officially as the spontaneous occlusion of the circle of Willis.

Moyamoya disease is known to have unique and dynamic nature to convert the vascular supply for the brain from internal carotid (IC) system to the external carotid (EC) system. ^, Insufficiency of this “ IC-EC conversion system ” may result in cerebral ischemia, as well as in intracranial hemorrhage from inadequate collateral vascular network, both of which represent the clinical presentation of moyamoya disease.

Clinical Findings and Preoperative Assessment

Symptoms and signs of moyamoya disease include brain ischemia and hemorrhage. Initial symptoms in moyamoya disease, both juvenile (younger than age 15 years) and adult cases considered together, are most frequently motor disturbances. In the experience of Suzuki, these were found in 36% of patients, followed by intracranial hemorrhage in 25%, headache in 20%, and convulsions in 6%. This is similar to the experience reported by Yamaguchi et al., who reported motor disturbances in 62.7% of males and 53.8% of females, disturbances of consciousness in 28.1% of males and 34.6% of females, signs of meningeal irritation in 10.3% of males and 20.5% of females, and speech disturbances 16.7% of males and 14% of females.

However, when these symptoms are studied with regard to age, large differences between juvenile and adult cases become apparent.

Among the juvenile cases, motor disturbances, including monoparesis, paraparesis, and hemiparesis are found in 60%, and in these juvenile cases, some 20% show motor disturbances indicative of transient brain ischemia.

If we also included other symptoms thought to be due to brain ischemia, such as sensory disturbances and mental and psychic disorders, then 85% of these juvenile cases show symptoms of brain ischemia. Intracranial hemorrhage was seen in only 4% of juvenile cases.

In other Japanese reported experiences, ^, ^, the onset of adult cases was accompanied by intracranial hemorrhage in 43% of patients, and symptoms due to brain ischemia, ^, including motor, mental, and psychic disturbances, were seen in 20% of these adult cases.

Diagnostic Criteria and Neuroimaging

Diagnostic Criteria

Original diagnostic criteria of moyamoya disease required bilateral steno-occlusive change at ICA with abnormal vascular network formation for the definitive diagnosis. ^, While considering the increasing number of patients with unilateral involvement as well as the evidence that substantial number of unilateral cases could progress to the bilateral presentation, diagnostic criteria of the definitive moyamoya disease was revised to include patients with both bilateral and unilateral involvement of terminal ICA stenosis associated with abnormal vascular network at the base of the brain with unknown etiology, as stated by the Research Committee of Moyamoya Disease of the Japanese Ministry of Health, Labour, and Welfare in 2015. Diagnostic criteria also state that definitive diagnosis of moyamoya disease requires catheter angiography in unilateral cases while bilateral cases could be promptly diagnosed by either catheter angiography or magnetic resonance (MR) imaging/angiography. Representative angiographic feature of moyamoya disease is shown in Fig. 45.1A and B . Angiographic finding of the carotid fork narrowing as the early stage characteristic of moyamoya disease is also shown in Fig. 45.1C .

FIGURE 45.1, Catheter angiography of an adult patient with definitive moyamoya disease. Anteroposterior view (A) and lateral view (B) of stage-3 moyamoya disease. Right carotid angiography showing moyamoya vessels (asterisks) . Carotid fork narrowing (C) as the early characteristic of moyamoya disease (stage 1).

Significance of Suzuki’s Angiographic Staging

Suzuki and Takaku1 classified the development of moyamoya disease into six stages. This staging does not represent the severity of patients’ condition, but may indicate the natural pathophysiological course of moyamoya disease. Insufficiency of this physiological reorganization system occurs at stage 3 in most patients, when the abnormal vascular networks at the base of the brain are most prominent.

Stage 1: Narrowing of carotid fork (see Fig. 45.1C ).
Stage 2: Initiation of the “moyamoya vessels”; dilatation of the intracerebral main arteries.
Stage 3: Intensification of the “moyamoya vessels”; nonfilling of the anterior and middle cerebral arteries (see Fig. 45.1A and B ).
Stage 4: Minimization of the “moyamoya vessels”; disappearance of the posterior cerebral artery.
Stage 5: Reduction of the “moyamoya vessels”; the main arteries arising from the ICA disappear.
Stage 6: Disappearance of the “moyamoya vessels”; the original moyamoya vessels at the base of the brain are completely missing and only the collateral circulation from the EC artery is seen ( Fig. 45.2 ).

This staging again represents the gradual conversion of the vascular supply for the brain from IC system to the external EC system; so called “ IC-EC conversion system .” ^, Initially, angiographic stage progression had been believed to be relatively rare in adult patients, but a recent multicenter observational study revealed that adult patients also had substantial risk of stage progression during the follow-up period.

Modern Supportive Diagnostic Tools

Definitive diagnosis of moyamoya disease is not always easy, especially in adult patients with early stage of Suzuki’s angiographic grading, when abnormal vascular network is not yet evident. To resolve this critical issue, it is important to understand the diagnostic value of high-resolution MR imaging focusing on vascular wall anatomy in moyamoya disease. Kaku et al. proposed the constrictive remodeling theory that outer diameter narrowing of the affected intracranial vessels was the early characteristic change of moyamoya disease as demonstrated by three-dimensional (3D) constructive interference in steady-state (CIISS) MR image. Ryoo and colleagues reported that moyamoya disease was characterized by concentric enhancement on distal ICA and shrinkage of middle cerebral artery (MCA), while atherosclerosis represented focal eccentric enhancement at the symptomatic segment of intracranial arteries. Alternatively, genetic analysis on the susceptibility gene, such as ring finger protein (RNF) 213 gene ( RNF213 ) in the 17q25-ter region, would also provide supportive information for the diagnosis of moyamoya disease among the East Asian population, although the exact function of RNF213 is undetermined. Further investigation of the functional role of the RNF213 is necessary to address the diagnostic value of the genetic analysis in patients with moyamoya disease.

Emergency Treatment

In the acute stage, the treatment is the same as for brain infarction or spontaneous intracerebral hemorrhage (ICH) due to other etiologies. In the event of ventricular hemorrhage, an external ventricular drainage operation is performed if the patient presents in acute evolution with signs of intracranial hypertension. ^,

In the case of ICH, initial medical treatment is indicated if the hemorrhage totals less than 25 cc in volume. If the hemorrhagic volume totals more than 25 cc, is associated with a lobar topography, and demonstrates mass effect over the midline structures, then surgical evacuation is indicated. In patients with ICH, infusion of osmotic agents is frequently used to control the intracerebral pressure and edema, and administration of anticonvulsants to control seizures is also required.

Bypass surgery in the acute stage of the disease is not indicated in light of the higher risk for perioperative complications. ^, ^,

Treatment in the Chronic Stage

Surgical Indication

Surgical revascularization prevents cerebral ischemic attack by improving cerebral blood flow (CBF) in adult patients with moyamoya disease. Direct revascularization surgery such as superficial temporal artery (STA)-MCA anastomosis is considered as a preferred procedure for the adult patients with moyamoya disease, providing long-term favorable outcomes. ^, Based on the guidelines for diagnosis and treatment of moyamoya disease, revascularization surgery is recommended for the patients with moyamoya disease manifesting as cerebral ischemic symptoms (Recommendation grade B). Regarding hemorrhagic-onset patients, STA-MCA anastomosis was also shown to reduce the risk of re-bleeding by a Japan Adult Moyamoya (JAM) trial, a multicenter randomized control trial to compare the incidence of re-bleeding rate between surgical and non-surgical groups of hemorrhagic-onset moyamoya disease. It was also reported that patients with hemorrhage at the posterior circulation territory demonstrated high re-bleeding rate (17.1% per year) while direct revascularization surgery significantly reduced the re-bleeding rate, indicating that patients with hemorrhage at posterior circulation territory should have apparent benefit from direct revascularization surgery. Finally, revascularization surgery for asymptomatic patients with moyamoya disease is currently not attempted because the natural history of asymptomatic patients is undetermined.

For the accurate preoperative hemodynamic evaluation, positron emission tomography (PET), single-photon emission computed tomography (SPECT), perfusion-weighted MRI, Xe ¹³³ -CT scan, and perfusion CT were used to confirm hemodynamic compromise on the symptomatic hemisphere. ^, Diminished cortical blood flow can also be inferred from fluid-attenuated inversion recovery (FLAIR) sequences showing linear high signals that follow a sulcal pattern, which is called the “ivy sign.”

Categories of Revascularization Procedure and Intra-Operative Care

There is no consensus on medical treatment with aspirin, other antiplatelet agents, anticoagulants, vasodilators, or corticosteroids to prevent future ischemic attacks in patients with chronic disease.

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