There are many types of normal variations of intracranial blood vessels, and some types of variations such as quantitative variation (increase or decrease of blood vessels), morphological variation (window opening, early bifurcation, stunted development), path variation (perpetual intranocular-extraneous artery anastomosis, perpetual common carotid-basal artery anastomosis) are often seen in daily work, and origin variation (two different blood vessels share the same origin) and other types of variation. Due to the large number of intracranial artery variants, some variants are rare and cannot be described in detail, so some of the more common cases of MRA variants are shared below.
1. Repetitive deformity
Repetitive middle cerebral arteries, either bilateral or unilateral, need to be distinguished from earlier middle cerebral artery bifurcation (usually less than 1.5 cm at the fork).
Cerebral artery duplication (eg, repeating middle cerebral artery, triple anterior cerebral artery, etc.) and odd cerebral arteries (such as odd anterior cerebral artery) are less common.
Second, the window opening deformity
Evalioring malformations: vascular localization repeats. Commonly found at the beginning of the basilar artery and in the M1 segment of the middle cerebral artery.
According to the pattern and size of the typing:
1. Fissure type, the windowing vessel is short (3-5mm), and it is fissured.
2. Convex lens type, the windowing vessel is slightly larger (5-10mm), and it is convex lens-like change.
3. Repetitive type, the range of open-windowed blood vessels is large (> 10 mm), and it is a lateral branch-like change.
A2 segment windowing malformation of the anterior cerebral artery needs to be distinguished from the double anterior communication artery and the anterior communication artery windowing malformation variant
Third, slender, absent, undeveloped
The A1 segment of the anterior cerebral artery is delicately developed
Anterior cerebral artery A1 segment deletion is not developed
The blood vessels in the lateral fissure of the middle cerebral artery are slender and narrow
Stenosis occlusion of the beginning of the left middle cerebral artery with open lateral branch circulation
The proximal posterior cerebral artery is slender and may present bilaterally or unilaterally
Localized stenosis of the middle of the posterior cerebral artery
Embryonic posterior cerebral arteries can be bilateral or unilateral, and are divided into complete (all blood supply comes from the internal carotid artery) and partial (blood supply comes partially from the internal carotid artery).
4. Permanent arteries
In the process of human embryonic development, there are 4 temporary pathways connecting the internal carotid artery and the basal artery, namely the primitive trigeminal artery, the primitive sublingual artery, the primitive atlantoaxial artery, and the primitive internal auditory artery, which are called perpetual intra-carotid-basal artery anastomosis if these pathways have not degenerated by adults, which is a rare congenital variation of intracranial vascularity.
The perpetual primordial trigeminal artery is a perpetual embryonic residual blood vessel that persists between the internal carotid artery and the vertebro-basal artery, and is a rare cerebrovascular variant with an incidence of 0. 1% ~ 0. 6% 。
5. Willis mutation deformity
A typical Willis ring consists of 10 blood vessels, including the bifurcation of the bilateral internal carotid artery (ICA), the A1 segment of the anterior communication artery (ACoA), the bilateral posterior artery (ACoA), the P1 segment of the bilateral posterior cerebral artery (PCA), and the basal artery (BA), in a hexagonal form. The Willis ring is divided into two parts: the pre-loop and the post-loop. The precircle includes the A1 segments of the bilateral ICA, ACOA, and bilateral ACA; the post-cycle includes the bilateral PCOA, the P1 segment of the bilateral PCA, and the BA. Only 42% to 52% of people can show a complete willis ring, and the willis ring variation includes the absence of blood vessels that make up them and changes in diameter, which are defined as dysplasia < l mm.
There are many typing methods for willi ring variations, so the types of variations are not discussed here, and relevant literature can be consulted for interest.
bibliography:
Fu Wenjun, DeMiao, Zhu Hui, et al. Willis ring variation and white matter lesions[J]. International Journal of Cerebrovascular Diseases, 2017(12).
Bai Tianjun,Zhou Hongjing,Pang Shanjun,et al. Application of 3DTOFMRA in the Diagnosis of Permanent Primitive Trigeminal Artery[J]. Journal of Medical Imaging, 2018(3).
Liang Yi, Tao Jingxiong, Li Zhen, et al. Characteristics of perpetual intrannocular-basal artery anastomosis of vascular lesions[J]. Journal of Clinical Neurology, 2017(1).
MAO Yipu, MA Longbai, HUANG Tao. Manifestations and clinical significance of CTA and MRA of perpetual endocular-basal artery anastomosis vessels[J]. Journal of Practical Radiology, 2015(6).
WANG Li;; Value of 3D-TOF MRA technique in the diagnosis of brain Willis ring variation[J]; Imaging research and medical applications; 2018（20）.
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Source: House of Magnetic Resonance
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