Anomalies and normal variants of intracranial arteries: an approach to...

Translation of the presentation “Anomalies and normal variants of the intracranial arteries: proposed workflow for classification and significance.”

Congress:	ECR 2016
Poster No.:	C-0199
Authors:	A. Hakim1, J. Gralla1, C. Rozeik2, P. Mordasini1, F. Pult1, L. Leidolt1, E. Piechowiak1, K. Hsieh1, M. El-Koussy1; 1Bern/CH, 2Loerrach/DE
DOI:	10.1594/ecr2016/C-0199
DOI-Link:	https://dx.doi.org/10.1594/ecr2016/C-0199

Translation into Russian: Simanov V.A.

1.1. Variants of origin (discharge) of vessels

1.1.1. Common origin : two different vessels can have the same origin (discharge)

SCA/PCA: 2-22% Fig.3 :

The common trunk arises from the basilar artery, then branches into the posterior cerebral artery (PCA) and the superior cerebellar artery (SCA) [1].

Hypoplasia of the posterior communicating arteries of the brain

Hypoplasia is a fundamental term in pathological anatomy, denoting underdevelopment of the tissues of a particular organ or the entire organism, which is determined by defects during embryonic maturation. Any organ can succumb to hypoplasia: arteries, heart, brain, kidneys, testicles or knee joint.

Intrauterine underdevelopment of an organ refers to disorders of adaptation and adaptation of the body. This disease is an irreversible process. Related concepts:

Aplasia is an extreme degree of underdevelopment of an organ that appears in a newborn in its rudimentary form.
Dysplasia is the abnormal formation of an organ.

The disease does not always manifest itself from the moment the child is born. Underdevelopment of an organ, if it is paired, can be compensated by another organ. For example, each kidney is 10% loaded. If one organ is hypoplastic, the other kidney will be 30-50% loaded. Often, a malformation is discovered by chance during a routine examination.

Causes

The following reasons give rise to it:

Hereditary factors. For example, one of the parents may carry a recessive gene, which, due to consanguineous marriages, manifests itself in the child. Characteristic of closed communities where incest is permitted. A striking example is cerebellar hypoplasia due to disruption of the VLDLR gene, which manifests itself in cases of consanguineous blood mixing.
Teratogenic factors: physical, biological and chemical effects on the body of the mother and child. For example, neuroinfections, living in areas with high levels of radiation, drugs that have not passed the teratogenicity test.
Injuries during pregnancy.
Maternal toxicosis.
Smoking, alcoholism and drug addiction of parents.
Pathologically reduced amount of amniotic fluid.

Symptoms

The specificity of the signs is determined by the localization of hypoplasia.

Hypoplasia of the cerebral artery

Underdevelopment of the arteries of the brain leads to a decrease in its blood flow due to a narrowing of the lumen or the absence of a vessel altogether. Due to the fact that the unit volume of blood circulation decreases, the supply of oxygen and nutrients to the brain decreases, which leads to the following symptoms:

constant fatigue;
headaches and dizziness;
sudden changes in blood pressure;
disturbance of the emotional state: irritability, excitability, intolerance to bright light or sound;
deterioration of cognitive functions: decreased general intelligence, slow thinking, low short-term memory, impaired concentration;
hypoplasia of cerebral vessels can provoke oligophrenia - congenital mental retardation of the child, since during intrauterine development the fetal brain did not receive the proper amount of blood and oxygen.

Hypoplasia of the posterior communicating arteries

Vascular underdevelopment leads to:

dizziness and nausea;
paresthesia: numbness, tingling, feeling of heat in the extremities;
diplopia – double vision;
deterioration of coordination.

1.2. Change in the number of vessels

1.2.1. Reducing the number of vessels

ICA agenesis: 0.01% Fig.11 , Fig.47 :

Around day 24 of embryogenesis, the ICA develops from the dorsal aorta and third arch. Subsequently, at approximately the 5th - 6th week, the base of the skull begins to take its shape. Thus, absence of ICA will result in absence of the carotid canal, identification of which is the most practical method in identifying this anomaly in a clinical setting. Typically, patients with ICA agenesis are asymptomatic due to well-developed collateral circulation through the ECA and vertebrobasilar system [2].

Aplasia of the A1 segment: 1-2%. Fig.12 and Fig.15 :

In this situation, both A2 segments are supplied by the existing A1 segment [2].

Azygos ACA: less than 1% Fig. 13 :

Both A1 segments form a common A2 segment, which supplies blood to both hemispheres[2].

Lack of Acom: 5% Fig.14 [2]:

Typically, the absence of the anterior communicating artery (Acom) is not easy to detect on time-of-flight MR angiography because the artery may be present but the flow signal is too weak to be visualized.

Lack of Pcom: 0.6% Fig.15 :

The posterior communicating artery (Pcom) is usually smaller than the P1 segment. Complete absence is rare [2].

Artery of Percheron: 4-11.5% Fig. 16 :

The thalamo-mesencephalic arterial supply can be divided into 3 types: type 1 is the most common, with perforating arteries on both sides arising from the P1 segments; type 2 , known as the artery of Percheron, arising from one of the P1 segments, supplying both sides; type 3 is an arch that connects both P1 segments and from which the perforating arteries arise [5].

1.2.2. Increase in the number of vessels

Incremental MCA: 2.7% Fig. 17 :

Literary definitions of accessory middle cerebral artery (MCA) and MCA duplication are quite dichotomous. In this paper, we use the definition of Teal et al., who limited the term “accessory MCA” to the branch arising from the anterior cerebral artery (ACA) and the term “duplicate MCA” to the artery arising from the distal segment of the ICA [6]. To distinguish an accessory MCA from a duplex one, the dominant vessel must be identified by carefully searching for the MCA bifurcation. Comparison with the contralateral side is also useful to find the level of ICA bifurcation [1].

Duplication: refers to two separate arteries that do not exhibit distal fusion. For example:

MCA duplication: 0.2-2.9% Fig. 18 : MCA duplication is an artery that arises from the ICA and runs parallel to the main trunk of the MCA. This variant should not be confused with early branching of the MCA, in which a short single M1 segment is present. It should also not be confused with the anterior temporal branch, which often arises from the M1 segment.
Acom doubling: 18% Fig. 19 [1].
SCA doubling: 14% Fig. 12 [2].

Trifurcation:

ACA trifurcation: 2-13% Fig. 20 : trifurcation refers to the presence of three A2 segments and is described by various names such as pericallosal triplex, arteria mediana corporis callosi and persistent primitive median artery of the corpus callosum [2]. Early origin of a frontopolar branch, for example from Acom, may appear as a third A2 segment.

MCA trifurcation: 12% Fig. 21 : The horizontal segment of the MCA is divided into superior and inferior trunks in approximately 78%. In 12% there is an additional (middle) trunk, this situation is called trifurcation, and the presence of more than 3 trunks, for example, quadrifurcation, is observed in approximately 10% Fig. 22 [2].

Fig. 11 Agenesis of the left ICA. TOF MRA (a), no signal from the flow in the left ICA. MIP CTA (c), CCA continues as ECA with no ICA. Bone window CT (b), absence of bony carotid canal on the left side. The normal carotid duct on the right side is marked with a red arrow for comparison.

Fig. 12 3D MRA, absence of A1 segment of ACA, both A2 segments extend from the contralateral side. Note the partial fetal PCA (white arrow), duplication of the superior cerebellar artery (blue arrow), and hypoplastic vertebral artery (red arrow) that terminates as the PICA.

Fig. 13 3D MRA, fusion of both A1 segments to form a single A2 segment (azygos ACA) (arrow).

Fig.14 3D TOF MRA, no Acom.

Fig. 15 3D TOF, absence of Pcom and A1 segment on one side. The significance of this option is that if the ICA is occluded on that side, there will be no possibility of collateralization through the circle of Willis. Incidental finding: aneurysm of the terminal portion of the contralateral ICA (arrow).

Fig. 16 MIP (a) and 3D TOF (b), type 2 thalamo-mesencephalic arterial supply (artery of Percheron) with a single arterial trunk (arrow) arising from the P1 segment, the branches of which supply blood to both sides.

Fig. 17 3D TOF, additional MCA (arrow) extending from the A1 segment.

Fig. 18 3D TOF of a duplicated MCA (red arrow) extending from the distal ICA. This artery should not be confused with the anterior temporal branch (white arrow), which is a common finding.

Fig. 19 3D TOF, Acom duplication (white arrows), proximal A2 segment fenestration (red arrow), A1 segment aplasia and complete fetal PCA (blue arrow).

Fig. 20 3D TOF, ACA trifurcation with three A2 segments (arrows), the third branch arises from Acom

Fig.21 3D TOF, MCA trifurcation with additional middle trunk.

Fig.22 3D TOF, MCA quadrifurcation.

How common is vertebral vascular hypoplasia?

Congenital changes in the location and size of the vertebral arteries are common: from asymmetry of both VAs to severe hypoplasia of one vertebral artery on cerebral angiography.

The absence of symptoms of vertebrobasilar insufficiency in people with hypoplasia indicates that even severe asymmetry of the vertebral artery is a normal variation and leads to an underestimation of the incidence of this anomaly. It is worth noting that hypoplasia of the right vertebral artery of the brain increases the risk of developing infarction of the inferior cerebellar arteries.

Variations of the cerebral arteries may be asymptomatic and cause no complications, although some of them increase the risk of developing an aneurysm and severe intracranial hemorrhage. The actual prevalence of these abnormalities in the general population remains unknown. Rapid technological advances in imaging and the availability of non-invasive angiographic studies will undoubtedly lead to an increase in the number of diagnosed anatomical variants among patients. The most common congenital variants deserve attention to avoid the complications they are associated with.

Advice! If a rare type of abnormality is detected on MRI or angiography, contact your doctor. In very rare cases, such congenital deformities require invasive intervention.

1.3. Change in morphology

1.3.1. Hypoplasia

ICA hypoplasia: 0.079% Fig. 23 :

In contrast to agenesis, the thin vessel is identifiable. Again, skull base tomography is useful in visualizing the bony carotid canal, which is thinner than normal in hypoplasia [2].

Hypoplasia A1: 10% Fig.24 :

Asymmetry of A1 segments is observed in 80% of cases. Hypoplasia is defined when the vessel diameter is less than 1.5 mm [2].

Hypoplasia A2 (bihemispheric ACA): 7% Fig. 24 :

One of the A2 segments is hypoplastic. In this variant, the blood supply to the ipsilateral hemisphere occurs mainly from the contralateral (dominant) A2 segment [2].

Hypoplasia Pcom: 34% Fig.25 :

but complete absence is a rare finding [2].

Hypoplasia of the vertebral artery:

50% on the right side (left dominant), 25% on the left side (right dominant), 25% codominant. In approximately 0.2%, the vertebral artery ends in the PICA Fig. 12 and Fig. 26 [7] [2]

1.3.2. Hyperplasia

Hyperplasia of the anterior choroidal artery: 2.3% Fig. 27 :

The anterior choriodal artery arises from the posterior surface of the terminal segment of the ICA, distal to the origin of the Pcom. This is usually a small branch. If it is enlarged (hyperplastic), then it supplies blood to part of the territory of the posterior cerebral artery (occipitotemporal branch) [1, 2].

1.3.3. Early bifurcation (early division):

Early MCA bifurcation: This is a common finding Fig.28 :

The horizontal segment of the MCA is usually 12 mm long, but may be shorter, with early branching (bi- or trifurcation) [1].

1.3.4. Fenestration: 0.7% including all intracranial vessels Fig. 6 , Fig. 19 and Fig. 29 . Fenestration is the division of the lumen of an artery into two separate channels. Each canal has its own endothelium and muscle layer and can separate the adventitia. These two canals merge distally. Fenestration is most often observed in the posterior circulation [1, 2].

Fenestration A1: 0-4% [1]
Fenestration A2: 2% Fig. 19 [1]
Acom fenestration: 12-21% [1]
Fenestration of the vertebral artery Fig. 29 : 0.3-2% [1].

Fenestration of the basilar artery Fig. 29 : 0.12-1.33%: the basilar artery is formed by the fusion of two longitudinal neural arteries. Incomplete fusion results in segmental fenestration, which is usually present in the proximal segment of the basilar artery [2].

Fig. 23 CTA (a), hypoplastic ICA (arrows). CT bone window (b) asymmetrical bony carotid canal

Fig. 24 3D TOF, hypoplasia of the A2 segment (white arrow) and the contralateral dominant A2 segment “bihemispheric ACA”. Note hypoplasia of the A1 segment (red arrow).

Fig. 25 MIP CTA, right Pcom hypoplasia (arrow). Note the pathological occlusion of the contralateral ICA.

Fig. 26 3D TOF, hypoplasia of the vertebral artery (white arrow) that ends as a PICA (green arrow).

Fig. 27 3D TOF, hyperplasia of the anterior choroidal artery (white arrow). The contralateral anterior choroidal artery is of normal caliber (green arrow). Red arrow points to fetal PCA, blue arrow to Pcom.

Fig. 28 3D MRA, early bifurcation with short prebifurcation segment M1 (arrow).

Fig. 29 Fenestration of the A1 segment (a), Acom (b), M1 segment (c), V4 segment (d) and the proximal part of the basilar artery (e).

Symptoms of circulatory disorders in the PCA

Clinical manifestations of impaired blood flow in the PCA depend on the location of the damage. These may be symptoms of damage to the midbrain, thalamus, occipital and parietal cortex.

Also, the clinic varies depending on the type of pathology. So, a stroke is an acute circulatory disorder, so symptoms develop suddenly and rapidly. And dyscirculatory encephalopathy, in turn, is a chronic disease. Consequently, the clinic progresses slowly, and for a long time no symptoms are observed at all.

The most specific disorder of blood flow in the posterior cerebral artery is ischemic stroke. This is a disease in which a vessel is blocked by a thrombus or embolus, which impedes blood circulation. As a result, necrosis (death) of a part of the brain occurs.

The following groups of symptoms are distinguished:

apical basilar artery syndrome;
visual disturbances;
mental disorders;
motor disorders.

Apex basilar artery syndrome occurs when blood flow is disrupted in the distal part of the vessel, before it divides into the right and left PCA. In this case, all brain structures that receive blood from the PCA are affected. The patient's consciousness is impaired, to the point of coma, his vision and psyche suffer. Motor function is often preserved.

1.4. Changing the course

1.4.1. Aberrant lateral pharyngeal ICA, tortuous ICA, and kissing carotid arteries:

During embryonic development, the ICA is thought to begin to unwind as the dorsal aortic root descends into the thorax, providing a direct pathway for the ICA. Failure in unwinding results in tortuosity of the ICA, which runs close to the midline of the posterior pharyngeal wall, called the aberrant lateral pharyngeal artery [6].

This morphology is more commonly seen in older patients or those with hypertension, but should not be confused with the fetal variant, although both have the same meaning (see below). The incidence of aberrant lateral pharyngeal ICA is approximately 5%, but the exact prevalence of the anomaly is unknown as it cannot be differentiated morphologically from tortuosity. Studies conducted by Ekici et al. showed that the least affected age group with ICA tortuosity was the younger age group [8].

The term "kissing carotid arteries" describes the elongated carotid arteries that meet at the midline; can be observed retropharyngeal or intrasphenoidal / intrasellar Fig. 30 [2].

1.4.2. Persistent primitive olfactory artery: 0,14%

The ACA is derived from the primitive olfactory artery, which regresses to form the recurrent artery of Heubner. Violation of regression leads to preservation of the primitive olfactory artery. This artery has an extreme anterior-inferior course in the A1 segment, which moves along the olfactory tract before the posterosuperior transition to the A2 segment, forming a hairpin-shaped configuration [9].

1.4.3. Persistent embryological anastomosis

+ persistent carotid-vertebrobasilar anastomosis:

During embryonic development, the anterior circulation supplies the hindbrain through several anastomoses, since the posterior circulation is not yet sufficiently developed. After the development of the vertebral arteries, these anastomoses regress. Impaired regression results in abnormal communication between the anterior and posterior circulation in the postnatal period. The most common form of these anastomoses is the fetal type PCA (see variants of origin/origin of vessels). Recognizing the course of these abnormal vessels, as well as the level of entry into the skull, is critical for their differentiation Table 1

persistent trigeminal artery (PTA): 0.1-0.2% Fig. 31 Fig. 48 : PTA originates from the cavernous segment of the ICA and communicates with the basilar artery. Proximal to the level of the anastomosis, the basilar artery is usually hypoplastic. On the angiogram, when viewed from the side, it has a characteristic “Trident of Neptune” or Tau sign configuration, reminiscent of the Greek letter “Tau” [1] [2]. There are two different classifications Table 2 Fig. 32 and Fig. 33 [10].

PTA variants (Saltzman III): 0.18-0.76%: Arteries that supply the posterior fossa, arising from the precavernous segment of the ICA and not communicating with the basilar artery [1].

Persistent auricular artery (otic artery): the rarest carotid-vertebrobasilar anastomosis. The existence of the auricular artery is controversial because it has not been identified in lower animals. It passes from the petrosal segment of the ICA to the basilar system through the internal auditory canal [2].

Persistent primitive hypoglossal artery (PPHA): 0.03-0.26% Fig. 34 Fig. 49 : This artery runs from the cervical segment of the ICA to the basilar artery through the hypoglossal canal. The vertebral artery is hypoplastic. CT scan of the skull base shows an enlarged bony hypoglossal canal [1, 2].

Proatlantal intersegmental artery: very rare. Connects the cervical segment of the ICA or external carotid artery (ECA) to the vertebrobasilar system. The artery enters the base of the skull through the foramen magnum, which allows it to be differentiated from the hypoglossal artery. There are two types:

Type I: joins the vertebral artery above the atlas.
Type II: enters the vertebral artery through the atlas [1, 2].

+ persistent internal-external carotid anastomosis

Aberrant intratympanic ICA: very rare. This variant is an anastomosis between the ICA and the ECA, as it is believed to arise from agenesis of the cervical segment of the ICA and the development of an anastomosis between the horizontal (petrosal) segment of the ICA and the enlarged inferior tympanic artery, which is a branch of the ECA. The ICA (or rather the enlarged inferior tympanic artery) in this case has a smaller diameter than the usual ICA, with the absence of the ascending part of the carotid canal as it enters the base of the skull, posterior and parallel to the jugular bulb, which resembles a mass in the hypotympanum; there is also no bone plate between the carotid canal and the tympanic cavity [1].

Persistent stapedial artery: 0.48%. This anomaly occurs due to the persistence of the anastomosis through the stapedial artery, which is usually present during development between the ECA and ICA. The artery arises from the petrosal segment of the ICA, passes through the obturator foramen, and ends as the MCA in the epidural space of the middle cranial fossa. A CT scan of the skull base may show a small canal near the carotid canal. Foramen spinosum, which contains MMA, will be absent. a persistent stapedial artery may be associated with an aberrant ICA [1, 2].

Table 3 shows the frequency of variants discussed, however, there are other rare variants that cannot be included in a single document. Finally, having a fully developed Circle of Willis can be considered an option since it is present in less than 50% of the population [2]

*NB: Frequency varies between authors depending on the type of study performed (CT, MRI, surgical or post-mortem). Frequency may also vary depending on geographic distribution; Published data may not always be applicable to other populations.

Table 1: Types of persistent carotid-vertebrobasilar anastomoses

Table 3: occurrence of anatomical variants

Fig. 30 Coronal MIP CTA of a patient with a history of hypertension shows elongated carotid arteries reaching the midline (“kissing” carotid arteries).

Fig. 31 3D TOF, lateral view (a) and dorsal view (b), persistent primitive trigeminal artery (red arrow) arising from the cavernous segment of the ICA and communicating with the basilar artery, which is hypoplastic to the level of the anastomosis (white arrow). In lateral view, the anomalous artery with ICA resembles Neptune's trident and the Greek letter "tau".

Fig. 32 MIP CTA of persistent primitive trigeminal artery (red arrow) in two different cases. According to Salas there are 2 types: medial sphenoidal or intrasellar (a), which extends into the sella turcica and perforates the dura mater or dorsum sella (green arrow), as in this case, and lateral petrosal or parasellar (b), in which the vessel goes with the sensory roots of the trigeminal nerve, on the side of the sella turcica.

Fig. 33 3D TOF showing two different cases of persistent primitive trigeminal artery (red arrow). Classification according to Saltzman: Type I (a), in which the PCA supplies the superior part of the basilar artery, including the posterior territory, and type II (b) with the fetal PCA (white arrow).

Fig. 34 3D CE MRA oblique (a) and posterior (b) views showing the persistent primitive hypoglossal artery (red arrow) which arises from the cervical segment of the ICA (green arrow) and continues as the vertebrobasilar artery (blue arrow). ECA is marked with a white arrow.

Instrumental diagnosis of stroke in the PCA

One of the methods of additional examination when diagnosing a stroke is computed tomography (CT). This is an x-ray method, the essence of which is the layer-by-layer imaging of organs and tissues due to the passage of x-rays through them. The disadvantage of this method is that it cannot detect ischemia of brain tissue in the first hours of a stroke. But early diagnosis is very important for effective therapy.

Sometimes computed tomography can be effective in the first hours. The radiologist may see a high signal intensity on the image, which is one of the earliest signs of ischemia.

A more advanced method is CT angiography. It can be used to determine the degree of blockage of the artery, the shape and size of the plaque. Variants of the anatomy of the posterior cerebral artery, its relationship to the surrounding brain tissue, and the development of collaterals are also assessed.

But the most informative method for diagnosing circulatory disorders is magnetic resonance imaging. This method does not involve passing x-rays through the human body. The image is obtained due to the presence of a magnetic field inside the tomograph, which detects the difference in the concentration of hydrogen ions in different tissues.

Magnetic resonance imaging allows you to see ischemic changes already in the first hour after a vascular accident. Also, using this method, it is possible to more accurately determine the location and extent of the pathological focus. Different modes make it possible to distinguish between acute and chronic circulatory disorders.

Meaning

The list in Fig. 35 shows the values of the anatomical options.

2.1. Recognition of anatomical patterns and the ability to distinguish them from pathological changes:

2.1.1. Knowledge of normal variations is part of the anatomical knowledge that is important for every radiologist and surgeon. Knowledge of normal variants and their proximity to other structures facilitates the understanding and diagnosis of various diseases, such as:

Trigeminal neuralgia, which can be caused by the presence of a variant of PTA (less commonly PTA), due to the proximity of the vessel to the trigeminal nerve [11].
Glossopharyngeal neuralgia or hypoglossal nerve palsy, which can be caused by a persistent hypoglossal artery [1].
Pulsatile tinnitus in cases of persistent stapedial artery [1].

2.1.2. Option against pathology:

Infundibulum: The Pcom infundibulum should not be confused with an aneurysm Fig. 36 .
ICA hypoplasia may be confused with dissection or fibromuscular dysplasia, while ICA agenesis may be confused with occlusion. Visualization of the skull base aids differentiation, as the bony carotid canal will be narrow in cases of hypoplasia and absent in cases of agenesis, but will appear normal in other acquired diseases Fig. 11 and Fig. 23 .
Different patterns of perfusion abnormalities may occur with normal variations that can cause confusion, especially in the context of stroke:

Asymmetry of CT or MR perfusion in the occipital lobes, in the case of unilateral fetal PCA. The contralateral side may show delayed perfusion because it is supplied by the posterior circulation Fig. 37 .
Bilateral perfusion delay in the occipital lobes compared with the frontal and parietal lobes may be observed in the absence of bilateral Pcom Fig. 38 .
Relative hypoperfusion in the PICA territory in cases of vertebral artery hypoplasia. Hypoperfusion may present as prolonged time-to-peak, prolonged main transit time, or decreased cerebral blood flow, but it never affects cerebral blood volume ) Fig.39 [12].

2.2. Hemodynamic effect of normal variants and abnormalities:

2.2.1. Understanding collateral function: The presence of hypoplasia or aplasia of segment(s) in the circle of Willis can affect collateral function when one or more arteries are occluded Fig. 15 .

2.2.2. Explains unclear cases of stroke:

Vascular conditions that cause changes in unexpected vascular territories can be explained by normal variations such as:

Ischemia in the posterior territory may accompany ICA pathology due to the presence of fetal PCA Fig. 40 .
Bilateral ischemia and ischemia in certain areas may draw attention to the presence of pathology in one of the options, such as:

Bilateral anterior infarction in case of thromboembolism of azygos ACA or dominant bihemispheric ACA Fig. 41 .
Bilateral mesencephalothalamic infarction with Percheron's artery Fig. 42 .

2.3. Association with vascular and nonvascular congenital anomalies and other diseases:

2.3.1. Association with aneurysms: Changes in vascular anatomy may be a sign of lack of vascular maturity and vulnerability to aneurysm formation. In the work of Lazzaro et al., normal variants of the circle of Willis were more common in cases with ruptured aneurysms than in cases of unruptured aneurysms [13]. Based on a review of the literature, the following variants and abnormalities were associated with aneurysms: Table 4 Fig. 43

Fenestrations: The incidence of aneurysms (IoA) is approximately 7% of all fenestrations. A defect in the media of the fenestrated segment and turbulent flow at both ends of the fenestration can lead to aneurysm formation. Additionally, in the work of Hudák et al., fenestration was a common finding in patients with unexplained subarachnoid hemorrhage due to a weak arterial wall [1] [2] [14]
ICA agenesis and hypoplasia: IoA 67% [2].
A1 segment aplasia: IoA14% [15].
Azygos ACA: IoA 41%. Due to increased flow from both segments of A1 [2].
Persistent dorsal ophthalmic artery: IoA 45% [4].
Persistent primitive olfactory artery: In the work of Uchino et al, 2 intracranial artery aneurysms were found in 14 patients with PPOA (IoA about 14%); one of them is in the hairpin bend (7%) [9].
PTA: IoA 14% [1].
Persistent hypoglossal artery: IoA 26% [16].
Proatlantal intersegmental artery: IoA 10% [1, 2]
Other variants and anomalies associated with aneurysms whose cases have been reported but not available include infraoptic ACA, superior anterior communicating artery, accessory MCA, MCA aplasia, variant PTA, and asymmetry of the circle of Willis [1, 2].

2.3.2. Association with other vascular anomalies and diseases:

Fenestration of the vertebral artery is associated with arteriovenous malformation in 7% [6].
PTA is observed in vascular anomalies such as AVM, carotid-cavernous fistula, and Moyamoya disease in 25% of cases [17].
Proatlantal intersegmental artery: The incidence of cerebrovascular disorders such as AVM, vein of Galen malformation and aortic arch variants is 59% [18].
Spontaneous vertebral artery dissection was slightly more common in subjects with hypoplastic vertebral artery than in controls (30.4% vs. 17.4%). It was also found that spontaneous vertebral artery dissection occurs more often with hypoplastic vertebral arteries than with dominant vertebral arteries (68% versus 32%) [19].

2.3.3. Association with other congenital anomalies:

Azygos ACA may be associated with holoprosencephaly and migration abnormalities Fig. 44 [1].
ICA hypoplasia is associated with anencephaly and basal telangiectasia [2].
Fenestration of the vertebral artery may be associated with vertebral fusion [6].

2.3.4. Association with other disorders:

Pituitary dysfunction and acromegaly in intrasellar “kissing” carotid arteries[2].
It was found that migraine with aura is more common in patients with an open circle of Willis [20].

2.4. Preoperative planning for cranial surgery, head and neck surgery, and neurointerventional procedures:

The description of normal variations is very important for surgeons and interventional radiologists, as some of these variations must be considered to avoid catastrophic consequences during intervention.

2.4.1. The risk of catastrophic hemorrhage exists in the following cases:

Transsphenoidal pituitary surgery in cases of PTA or intrasellar “kissing” carotid arteries.
Middle ear surgery in cases of persistent stapedial artery and aberrant intratympanic ICA.
Pharyngeal surgeries such as otopharyngeal tumor resection, tonsillectomy, adenoidectomy and palatopharyngoplasty in cases of aberrant lateral pharyngeal artery.

2.4.2. Knowledge of normal variations is important in interventional procedures. This knowledge may help to gain vascular access, such as dominant versus hypoplastic vertebral or variant access, or avoid complications during procedures such as tumor embolization through ECA catheterization in cases of MMA arising from the ophthalmic artery, which can lead to blindness . Fig.45 Fig.50

2.4.3. The presence of persistent carotid-basilar anastomoses should be excluded before certain procedures, such as the Wada test: in this case, injection of amytal can lead to loss of consciousness and apnea [2]

Fig.35 Meaning of normal options

Table 4: Variants associated with aneurysms and their occurrence

Fig. 36 3D TOF MRA, funnel-shaped dilatation with origin of Pcom (white arrow), which should not be confused with an aneurysm. Note the small aneurysm at the origin of the contralateral Pcom (red arrow). Also note the trifurcation of the ACA.

Fig. 37 MR perfusion, TTP map (a) shows slow perfusion in the left occipital lobe; no abnormalities were found in other perfusion parameters. 3D TOF (b), showing fetal PCA on the contralateral side (arrow).

Fig. 38 TTP perfusion map (a) shows a symmetrical delay in the occipital lobes, no deviations in other perfusion parameters were noted. 3D TOF shows no Pcom on both sides.

Fig. 39 (same patient as in Fig. 12) with hypoplasia of the right vertebral artery, which ends as the PICA. TTP map shows perfusion delay in the territory of the right PICA. An examination performed 6 weeks later for other reasons (not shown) showed no pathology in this area.

Fig. 40 MRI of a 56-year-old patient complaining of headache shows dissection of the left ICA (red arrows) with intramural hematoma on T2 (a) and T1FS (b). DWI (c) and ADC (d) show subacute infarction in the territory of the left PCA, which is due to the presence of fetal PCA (TOF not shown).

Fig.41 72-year-old patient with hemiplegia, epilepsy and impaired consciousness. DWI (a) and ADC (b) show bilateral infarcts in the ACA territory. DSA (c), shows proximal occlusion of the azygos ACA (arrow).

Fig. 42 Bilateral acute thalamic infarctions on DWI (a). DSA shows occlusion of the P1 segment of the left PCA (b). Minimal recanalization after intra-arterial thrombolysis (c), with mild opacification of the artery of Percheron (arrows) arising from the left PCA.

Fig. 43 Aneurysms (arrows) associated with abnormalities; a) A1 aplasia with Acom aneurysm. b) Azygos ACA with pericallosal aneurysm. c) fenestration of the basilar artery with proximal basilar aneurysm after coiling.

Fig. 44 Axial (a) and sagittal (b) MRI images of a child with holoprosencephaly, anterior cingulate fusion, and abnormal beak and genu corpus callosum. Note the empty flow of the anterior cerebral artery (arrow), which is single (azygos) and displaced anteriorly.

Fig. 45 55-year-old patient involved in an accident. Initial CT scan (a) shows a fracture of the left temporal bone. She later complained of pulsating tinnitus. DSA (c) with flat panel CT angiography (b and d) was performed. Reconstructed images showed the middle meningeal artery (yellow arrows) arising from the ophthalmic artery (blue arrow) and the traumatic AVM (red arrows) draining into the external jugular vein to form an aneurysm (orange arrow). Knowledge of this option is important when planning therapy.

Features of visual, mental and motor disorders

Visual impairment occurs when the occipital zone of the cerebral cortex, optic radiance and geniculate body are damaged. In this case, there is a complete loss of the field of vision on the opposite side. For example, if the occipital cortex on the right is affected, a person is unable to see the left half with both eyes. The right visual field remains unaffected. Sometimes not half, but a square of the field of view falls out.

If the occipital region is affected on both sides, the visual impairment may be more complex. Visual hallucinations occur, the patient does not recognize familiar faces or colors. A rare pathology with circulatory disorders in the posterior cerebral artery is Anton's syndrome. In this condition, a person does not realize that he is completely blind.

Psychological disorders occur when the corpus callosum and occipital lobe are damaged. The person is unable to read, but the ability to write is preserved. If a person is right-handed, such changes are possible if the blood circulation in the left PCA is impaired. When a large area of the cortex is damaged, amnesia and psychiatric disorders (delirium) occur. If extensive necrosis of the thalamus occurs, the patient may develop Dejerine-Roussy syndrome. It manifests itself with the following symptoms:

disturbance of sensitivity (tactile, temperature, pain);
severe pain on the entire half of the body opposite the localization of the lesion in the thalamus;
lack of movement on the opposite half of the body;
involuntary spontaneous movements in the limbs;
sensation of goosebumps, flies crawling across the skin on half of the body.

Motor disorders in the form of weakness of the upper and lower limbs on one side are observed in 25% of patients. This symptom is called hemiparesis, and occurs on the side opposite to the location of the blockage.

The most common cause of motor disorders is a violation of the blood supply to the cerebral peduncles. However, it is possible to develop paresis without damaging this structure. In such patients, movements are impaired due to compression of the internal capsule by the edematous thalamus.

In 25% of patients, a stroke in the vertebrobasilar area imitates blockage of the vessels of the sinocarotid area. Sometimes it is difficult to distinguish them from each other due to the patient’s speech disorders, sensory and motor disorders. Therefore, when diagnosing blood flow disorders in the posterior cerebral artery, it is so important to use additional examination methods.

Abbreviations:

A1: Horizontal segment of ACA
A2: Vertical segment of ACA
ACA: Anterior cerebral artery
Acom: Anterior communicating artery
AICA: Anterior inferior cerebellar artery
AVM: Arteriovenous malformation
BA: Basilar artery
CBF: Cerebral blood flow
CBV: Cerebral blood volume
CoW: Circle of Willis
DSA: Digital subtraction angiograph
ECA: External carotid artery
ICA: Internal carotid artery
IoA: Incidence of aneurysms
M1: Sphenoidal segment of MCA
MCA: Middle cerebral artery
MMA: Middle meningeal artery
MTT: Mean transit time
PCA: Posterior cerebral artery
Pcom: Posterior communicating artery
PDOA: Persistent dorsal ophthalmic artery
PICA: Posterior inferior cerebellar artery
PPHA: Persistent primitive hypoglossal artery
PPOA: Persistent primitive olfactory artery
PTA: Persistent trigeminal artery
SCA: Superior cerebellar artery
sVAD: Spontaneous vertebral artery dissection

Results

The posterior cerebral artery and its branches supply almost the entire posterior part of the brain. The cortex and underlying structures receive blood from its pool: thalmus, midbrain, internal capsule, corpus callosum and others. It is thanks to the normal blood flow in these vessels that we can see, move, and think. Therefore, it is so important to know the symptoms of impaired blood flow in the posterior cerebral artery. Timely seeking medical help will allow effective treatment to be prescribed as early as possible.

Time plays an extremely important role in acute cerebral circulatory disorders. Early therapy increases the chances of successful rehabilitation of the patient.