Pediatric stroke. Revascularization and reconstructive surgery in children with cerebrovascular disease. E. V. Shevchenko
important property of a deformation is its hemodynamic significance determined by the growth degree of the linear blood flow rate (LBFR) in the deformation area due to its local contraction, thus reflecting the intensity of septal stenoses and twist of the artery without distal hypoplasia signs and decrease of volumetric blood flow in the deformed artery. The tortuosity is considered hemodynamically significant, when the increasing LBFR in the deformation area exceeds 170 cm/s (moderate significance). If the LBFR exceeds 250 cm/s, it is considered as evident hemodynamic significance, and when it exceeds 300—350 cm/s with the presence of a turbulent noise – as rough [26].
Fig. 3: Types of pathological deformations based on CAG: A – C-shaped tortuosity of ICA (arrow indicated); B – S-shaped tortuosity of ICA (arrow indicated); C – ICA loop (arrow indicated).
According to literature data, a forward course of major vessels is noted in 65—70% of persons, vascular deformations – in 23—40%, including the pathological, hemodynamically significant tortuosities – about 9—16% of cases. According to data of J. Weibel and W. Fields (1965), C- or S-shaped course of a vessel elongated approximately by 4 cm occurs twice more often unilaterally than bilaterally. Other types of pathological deformations are revealed equally often, regardless of the gender and the age, while unilateral pathological deformations occur also twice more often than bilateral [14; 20]. Hemodynamically significant, pathological tortuosities cause both acute cerebrovascular diseases and chronic cerebrovascular insufficiency. While a child grows, the pathological tortuosity of the ICA may be leveled completely or the artery may get «straightened», which is accompanied by a recovery or an improvement of the blood flow and the regression of neurologic disturbances [14].
Moyamoya is a rare disease [208] characterized by a progressive spontaneous stenosis or occlusion of a supraclinoid segment of an ICA (single or both) at the level of the siphon and the initial segments of the anterior cerebral artery (ACA) and the middle cerebral artery (MCA) with the subsequent involvement of the VBS. The specific feature of this disease is the secondary formation of a basilar, anastomotic capillary network, resembling a small cloud of smoke (Fig. 4) during the angiographic imaging, which is pronounced in Japanese as «moyamoya». This word has become an official name of the disease. In 40% of cases in the moyamoya disease a bilateral impairment of the ICA is noted; initially the ICA is involved only on one side [233; 285]. The «moyamoya syndrome» term is more often used for angiographic description of the pathology [266].
Fig. 4: MRA of a patient with the moyamoya disease. The secondary formation of anastomotic network resembling a cloud of smoke is indicated with an arrow.
According to data from various sources, the «moyamoya» term was first used by A. Takeuchi and J. Suzuki in 1969 [254]. According to other data, the discovery of this disease is related to an earlier period, when in 1937 K. Shimizu implemented the carotid angiography technique in Japan [205]. Shortly after the World War II, neurosurgeons started to apply this type of test actively, which permitted to diagnose and to study the moyamoya disease. It was found then that this pathology can be often seen in the countries of South-East Asia. The research works by A. Takeuchi, K. Shimizu (1957), N. Moriyasu (1964), T. Kudo (1968), J. Suzuki and A. Takaku (1969) have contributed a lot into the worldwide awareness and study of the disease.
It was shown that the highest morbidity rate of the moyamoya disease in the world is noted in Japan – 4—5 incidents per 100,000 population annually. By way of contrast, in 2005 in America the morbidity rate of the moyamoya disease was 0.086 incidents per 100,000 population [266]. R. Smith and J. Scott (2012) claim that in America the moyamoya disease rarely occurs in children – 1 incident per 1,000,000 – and becomes the cause of 6% of all pediatric strokes [243]. According to data of various European clinics, for the last 5—6 years the number of patients, especially children, with the moyamoya disease has increased in Europe, and it still continues growing [139]. Such a tendency might be connected with the improved diagnostics of cerebrovascular diseases, although this issue is studied little. Some prevalence of the morbidity is noticed in women (the ratio of female and male patients is 1.6:1). I. Ahn et al. (Korea, 2014) analyzed the statistical data for the period from 2007 till 2011. In 2011 the total number of patients with the moyamoya disease was 8,154 in Korea, during the period from 2007 till 2011 the morbidity was recorded on the level of 2.3 per 100,000 people, while in 2011 it was 16.1 per 100,000 people; the ratio of female and male patients was 1.8:1 [41].
In Russia there are singular publications about this disease [15; 18; 29].
The moyamoya disease has two age-related peaks of clinical manifestation: the first one comes on children at the age of 5—10 years old, while the second one – on the age of 30—40 years old [258; 266]. The pathologic process is most active approximately until the age of 10 years, and it gets stabilized approximately by the age of 20 years [208; 270].
The etiology of this disease is actively discussed, although it still remains unknown [208]. It is supposed that the moyamoya disease may be either congenital or acquired [133]. It is noticed to be associated with other systemic and non-systemic diseases (Down’s syndrome, neurofibromatosis type I, autoimmune diseases, tuberous sclerosis, atherosclerosis, fibro-muscular dysplasia, thalassemia and sickle-cell anemia, thyroid disorders) as well as with radiation therapy of basilar gliomas in children with a craniocerebral injury [135; 175; 224; 234; 270].
Hereditary factors play an important part in the moyamoya disease [196; 277]. There are some known familial cases of the disease. According to some data, this disease has a familial nature approximately in 15% of patients. Due to this, over the latest years the attempts have been made to find a genetic base of the disease. Some data were published on the detection of the locuses associated with the moyamoya disease on 3, 6, 8 and 17 chromosomes. In 2008 some data were published about the autosomal dominant inheritance (the gene was mapped to chromosome 17q25) of the moyamoya disease [119; 130; 197; 199; 225]. However, in the literature there is a description of the moyamoya disease in one of two twins, and this permitted the authors to conclude that this disease was not rigidly determined [256]. In one of their latest works J. Ma et al. report (China, 2013) that while studying the associative genetic predisposition, they have found the connection between the moyamoya disease and genic polymorphisms in RNF213 gene (p.R4859K and p.R4810K), which is more common in Japan and Korea, but less common in China [171].
Despite these studies, the genetic screening in the moyamoya disease has not become widely common, because its efficacy was not proved [233]. As of today, the researchers studying this problem think that this disease has a multi-factor nature [266].
As already stated above, the pathophysiology of the moyamoya disease consists in the gradual constriction of major stems of basilar intracranial arteries due to deposits of lipids in the intima in the absence of inflammation signs. The middle layer of arteries is thinned, the adventitia is not involved into the process. Similar changes in vessels may be observed in other organs, which shows that the vascular impairment has a systemic nature. The involvement of the immune system into the process is not ruled out [270]. In some authors’ opinion, inflammatory proteins participate in the development of the disease [287]. Anyway, intra- and extra-cranial vascular anastomoses are formed on the base of the brain during the progressive occlusion process in the vessels of the Willis’ circle [270; 277], which, to a certain degree, compensates for critical decrease of the regional cerebral blood flow, but leads to a gradual growth of chronic cerebral ischemia mostly in the cortical sections of big hemispheres [208; 266; 291]. The anastomotic capillary network is disappearing, while collaterals are developing from the ECA (meningeal collaterals are called «a magic network») [208; 291]. Arterial aneurysms frequently occur in the moyamoya disease. According to some data, the detection rate of VBS aneurysms reaches 62%, which several times exceeds the incidence of this pathology in the population