*Neuropsychology of Moyamoya Disease DOI: http://dx.doi.org/10.5772/intechopen.96558*

on brain MRI but no evidence of grey-matter damage. Significant cognitive impairment, defined as half of the test scores 1 S.D. below the average mean, was present in 7 patients (23%). Executive functioning, mental efficiency, and word- finding were the ability areas most frequently impaired, whereas memory was relatively intact [57]. Comparable cognitive findings were also observed in the subset of 10 patients (33%) with entirely normal static brain MRI, which lead the authors to conclude that cognitive impairment in MMD can occur in the absence of ischemic stroke as manifested on MRI. As the reader will note, executive dysfunction remains a consistent finding between studies, and Mogensen demonstrated that this impaired executive functioning in adults with MMD is most strongly associated with secondary damage to the brain parenchyma in the form of White Matter Disease (WMD) or cortical stroke [63]. They suggested that increases in global WMD burden were a good indicator of cognitive decline. They also showed that patients with higher baseline CBF tend to have better cognitive functioning.

The treatment for MMD usually consists of surgical revascularization techniques, involving dissecting and re-routing a branch of a superficial artery to a distal branch of another. Revascularization surgery augments cerebral blood flow, and such perfusion augmentation may engender cognitive and neurologic improvement even beyond focal regions of established ischemia. The influence of surgical revascularization treatment on the cognitive status of MMD patients is a subject of debate. This approach is favoured over medical management in children in most cases, but limited data are available regarding the effectiveness of an arterial bypass in adults, especially in terms of cognition improvement. Indeed, there are few published cases reporting neuropsychological status pre- and postrevascularization. Jefferson et al. [64] reported the first case of a 48-year old woman who underwent revascularization following a right hemisphere stroke, and showed a clear temporal relationship between the vascular effects of the bypass procedure and an improvement in neurocognitive status. Preoperative performance in tasks involving visuospatial perception, organization, and construction was generally impaired compared to her estimated premorbid abilities, while postoperative visuospatial performance improved to within a normal range. However, nonverbal visuospatial memory did not return to premorbid levels [64]. Some years after this study, a group of 33 adult patients was assessed pre- and post-surgery in Coutinho's report regarding speech, memory and intellectual processes, in which all the patients underwent stabilization or improvement of physiological symptoms together with significant cognitive improvement after surgery [65].

Another study evaluated a larger group of patients (84) in whom postoperative results were dissapointing: 14% showed significant decline and only 11% an improvement. The majority of patients (75%) displayed neither a significant decline nor an improvement in neurocognitive performance after EC-IC bypass surgery, and similar results were obtained when the analysis was confined to those who underwent unilateral or bilateral revascularization [66]. In light of the fact that adult MMD patients can either improve or decline cognitively after revascularization surgery, Yanagihara et al. [67] emphasized that the intervention boosts cerebral blood flow (CBF) and improves cerebral oxygen metabolism. This cerebral hyperperfusion, which is short-term, can induce a significant increase in ipsilateral CBF that greatly exceed the brain's metabolic needs, thus representing a complication. The authors noted that cerebral hyperperfusion can produce widespread, though minimal, injury to the ipsilateral white matter and cortical regions. In their study of 32 patients, neuropsychological assessments demonstrated cognitive improvement in 31%, no change in 25%, and a decline in 44%. Based on brain perfusion SPECT and symptoms, ten patients were considered to have cerebral hyperperfusion syndrome, and all of these patients exhibited a postoperative decline in cognition.

In summary, acute-stage cerebral hyperperfusion after arterial bypass surgery would seem to impair cognitive function.

On the other hand, an increase in CBF in the chronic stage of cerebral hyperperfusion improves cognitive function in adult patients with symptomatic ischemic MMD [67]. In Moyamoya angioplasty, increased apparent diffusion coefficient (ADC) in frontal white matter (WM) with a normal appearance has been associated with frontal hypoperfusion and executive dysfunction.

Multiple burr-hole surgery enables the revascularization of large frontal areas. In this sense, Calviere et al. recently assessed the effect of such surgery on the ADC and cognitive functions in fourteen adults treated with angioplasty before and six months after the intervention [68]. ADC was obtained from regions of interest located in frontal and posterior (temporo-occipital) normal-appearing WM. Ten patients underwent neuropsychological assessment of executive and attentional functions before and after surgery. The authors concluded that, in MMD adults treated with angioplasty, indirect revascularization by means of burr-hole is followed by a decrease of ADC in normal-appearing frontal WM and may improve some executive functions in the flexibility process. Alterations of ADC may reflect an improvement in cerebral perfusion after surgery. Therefore, the measuring of ADC may be a promising tool to explore potentially reversible microstructural WM damage related to hypoperfusion and cognitive change in aMMD.

In non-surgically treated adult MMD patients with onset of ischemia and stable hemodynamics, the cognitive course remains unclear. In the pool of 70 patients in the study by Miyoshi et al. [69] patients without recurrent ischemic events and no hemodynamic compromise displayed intact cognitive functions two years after the last event. Notably, due to controversy surrounding the surgical option, a large proportion of the patients chose conservative treatment, especially those with hemorrhagic MMD [69]. A study by Su et al. employed the MoCA test to assess cognitive function in 26 adult patients with hemorrhagic MMD who received no surgical revascularization, and observed Mild Cognitive Impairment (MCI) after two years in all 26 [70]. These patients obtained significant decreases in all MoCA subscores (P = 0.000) regarding delayed recall, visual space and executive function. However, in a longitudinal case series of adults who had suffered stroke secondary to MMD, stroke recovery was good providing the patient was treated transdisciplinary for 3-4 months (as well as being young and healthy and highly functional prior to the stroke) [71]. The functionality of the patients seems to be more critical than supposed. In Araki's [56] study, the ten patients, were divided into those without difficulties maintaining social independence, with higher educational background, better socioeconomic status, no need for public support, and those who had social independence issues and were socioeconomically disadvantaged. The study found subtle impairments in intelligence and working memory in all the sample. However, frontal lobe functions were primarily affected in adult MMD patients with a social independence problem, even if brain imaging techniques did not reveal noticeable abnormalities [56].

All the questions mentioned above were studied in the meta-analysies of cognitive functions performed by Kronenburg et al. [44], and which included 17 studies (11 studies reporting on 281 children, six on 153 adults). Regarding the adult samples, the median percentage with impaired cognition was as high as 31% (range, 0% to 69%), their median I.Q. scores were within the normal range (95; in a range of 94 to 99), and the median z-scores of cognitive domains were between –0.9 and –0.4, with many of them being affected. The highest median percentage of impaired function was detected for domain attention and executive functions. In a previous review, these authors had suggested that cognition is affected more frequently in children than in adults, reporting intelligence to be impaired in children,
