Endovascular Treatment Of Distal Cerebral Health And Social Care Essay

1. ABSTRACT

Background and Purpose:

The aim of this retrospective study was to report the incidence, clinical presentation and imaging results of endovascular treatment of 20 cases of distal cerebral aneurysms.

Materials and Methods:

From January 2010 to end of December 2012, 1520 aneurysms were treated in our institution. Among them 389 were treated by endovascular procedure. 20 aneurysms were located on distal cerebral arteries (incidence, 1.3%). There were 8 men and 12 women, ranging from 6 to 58 years of age (mean 32years).sixteen patients presented with subarachnoid and four with intracranial hemorrhage and most patients were in poor clinical condition on admission. Aneurysm location were as follows : 7 middle cerebral artery , 4 anterior cerebral artery, 3 posterior cerebral artery , 3 anterior inferior cerebellar artery , and 3 posterior inferior cerebellar artery . All patients were undergone endovascular therapy.

Results:

Seventeen aneurysms were treated by parent artery occlusion and three without parent artery occlusion among them coiling was done in 6 cases, Onyx 500 on 1case, Onyx 18 on 11 cases and coiling & Onyx occlusion on 2 cases. Clinical follow-up was at a mean of 19 months (range, 2–36 months). 16 patients recovered completely without any neurological deficit.

Conclusion:

Distal cerebral artery aneurysms are rare. Most patients present with poor-grade hemorrhage. Endovascular parent vessel occlusion is effective in excluding the aneurysm. In most patients, adequate collateral circulation prevents infarction in the territory of the occluded vessel. Control of blood flow within the aneurysm is essential in order to preserve the parent artery and avoid reflux of glue into the feeding pedicle. Significant experience and skill in glue injection of brain is mandatory for obtaining perfect control of the procedure. Whatever their location, with glue can become an established therapeutic approach while with coils, detachable platinum coils are deployed through micro-catheter to fill the aneurysm and prevent it from further expansion and rupture.

Key Words: Aneurysm, distal, endovascular

2. INTRODUCTION

Aneurysms located on distal portions of the cerebral arteries are uncommon, and their underlying pathology, clinical presentation, natural history, and clinical management are poorly understood, they have unclear origin [1, 2]. The approach to treat distally located aneurysms is difficult [3]. Endovascular methods are minimally invasive therapeutic approach, which can less some of the danger in the patient associated with craniotomy and open surgical clipping [4]. Several approaches have been proposed to surgically treat these aneurysms, depending on their size and locations [1]. Although direct clipping is possible in some cases in post circulation, sophisticated surgical techniques such as hypothermic cardiac arrest and bypass construction are often needed. On the other hand, endovascular therapy, consisting of occlusion of the parent artery with coils or glue, is simple to perform and often effective [5]. However, this deconstructive approach may lead to infarctions in the territory of the occluded cerebral artery if collateral circulation is insufficient [6]. The aim of this retrospective study was to report the incidence, clinical presentation, and midterm clinical and imaging results of endovascular treatment of 20 cases of distal cerebral artery aneurysms.

METHODOLOGY

Patients Characteristics

Between January 2010 and December 2012, 1520 patients of aneurysm were treated in our institution. Among them surgery was performed in 1131 and endovascular treatment in 389 patients. 20 patient’s aneurysms were located on distal cerebral arteries, which were treated by endovascular techniques. There were 8 men and 12 women with a mean age of 32 years (range, 6-58 years). Seventeen patients presented with subarachnoid hemorrhage, and three patients with intracranial hemorrhage. Eight of 20 patients who presented with hemorrhage were in poor clinical. Locations of the aneurysms were as follows: 7 middle cerebral artery (MCA) , 4 anterior cerebral artery (ACA) ,3 posterior cerebral artery (PCA), 3 anterior inferior cerebellar artery (AICA) , 3 posterior inferior cerebellar artery (PICA) .

Technical Procedure

Endovascular procedure

Endovascular treatment was performed with the patient under general anesthesia on a (FD 20 Philips Medical System). On this unit, 3D angiography is available. The type of endovascular treatment depended on the anatomy of the aneurysm neck and parent vessel as well as on the location of the aneurysm. Endovascular procedure is a percutaneous approach to treat an intracranial aneurysm within the blood vessel without the need of a craniotomy, a microcatheter is inserted into the femoral artery near the groin and navigated to the site of the aneurysm .there are two procedure for endovascular treatment one with glue and other with coiling. Aneurysms were embolized with a flow guided microcatheter and glue is slowly injected into the aneurysm and next way with coils, detachable platinum coils are deployed through microcatheter to fill the aneurysm and prevent it from further expansion and rupture. Improvements in catheter technology have made distal aneurysms more accessible for endovascular procedure.

4. RESULTS

Aneurysms were treated by coil or glue and in some cases with both. Among 20 cases parent artery occlusion were done in 17 and 3 cases without parent artery occlusion. Sixteen patients presented with subarachnoid hemorrhage and four with intracranial hemorrhage, most patients were in poor clinical condition on admission. The aneurysms location were ;7 in the middle cerebral artery ,4 in the anterior cerebral artery ,3 in the posterior cerebral artery ,3 in the anterior inferior cerebellar artery , and 3 in the posterior inferior cerebellar artery

Follow up

Clinical follow up was carried out by neurologists, interventional neuroradiologists and or neurosurgeons. All 20 patients survived the hospital admission period. Clinical follow-up was at a mean of 19 months (range, 2–36 months). In 7 of 20 patients infarctions in the territory of the occluded cerebral artery (or the branch of the cerebellar artery) were apparent on follow-up MR imaging or CT; the remaining 13 patients had no infarctions. 3 of 7 patients with a partial or complete MCA occlusion developed a small clinically silent infarction. Two of 3 patients with a PICA occlusion developed partial PICA infarction. In 1 patient with a distal AICA aneurysm with facial and vestibule-cochlear nerve palsy accompanying hemorrhage. One of 4 patients with ACA developed clinically silent infraction (Table 1).

Representative Cases

Case I: A 10 years old Female presented with sudden terrible headache. On examination, no neurological deficit was found. CT showed the crack SAH of the right side. DSA ​​revealed right middle cerebral artery M3 segment aneurysm with neck measuring 1.5x2mm

Figure 1 Preoperative four vessel DSA of Case I (A and B), right Internal cerebral artery DSA shows the MCA M3 segment aneurysm

Figure2. Microcatheter angiography (C) and postoperative DSA (D and E) of Case I demonstrating right MCA M3 segment embolization in situ and embolized aneurysm with coil packing.

Case II: A 30 years old male non diabetic, non hypertensive, with disturbance of consciousness and motor aphasia was admitted in our hospital. Patient was non alcoholic and non smoker. On examination, DSA revealed a 2mm x 2mm Middle Cerebral Artery M5 segment Aneurysm

Figure 3 Preoperative four vessel DSA of Case II(A and B), Right ICA demonstrating MCA M5 segment aneurysm

Figure 4 microcathter angiography (C) and post operative (D) DSA showing embolized aneurysm with Onyx18 glue

Case III: A six years old female, presented with SAH. Neurological examination was within normal limit. The etiology of distal MCA aneurysm was uncertain the patient did not have a clear history of trauma DSA found middle cerebral artery M4 aneurysm

Figure 5 Preoperative four vessel DSA of Case III (A and B), Right ICA revealing M4 segment aneurysm

Figure 6 Per operative (C) and post operative (D) DSA of Case III showing embolized M4 segment aneurysm with Onyx18 glue

Case IV: A 37 years old male patient came after trauma in road traffic accident. Hematological and laboratory examination indicated no abnormalities. no cardiac diseases and bacterial infection .DSA revealed the right middle cerebral artery M3-segment aneurysm, managed by embolization with micro-coil.

Figure 7 Preoperative DSA of Case IV (A, B, C, D), right ICA showing MCA M3-4 segment aneurysm

Figure 8 Per-operative (E F) and post operative (G H I) DSA showing embolized M3-4 segment aneurysm with coil X2

Case V: Male, 20 years of age, whose CT scan showed left occipital brain hemorrhage and had been diagnosed as having left occipital lobe AVM, two years back. DSA shows a left side P3 segment pseudoaneurysm, which was managed by onyx 18 glue embolization.

Figure 9 Preoperative four vessels DSA of Case V (A, B), Left BA describing left P2 segment aneurysm

Figure Number 10 microcatheter angiography (C, D) and post operative (E) DSA showing embolized P2 segment aneurysm with Onyx18 glue.

Case VI: Female, 8 years of age experienced a sudden onset of headache, nausea and vomiting followed by loss of consciousness and was referred to our center after a road traffic accident. CT shows SAH, DSA was suggested which revealed left P4 segment pseudoaneurysm, managed by onyx 18 embolization

Figure 11 Figure 9 Preoperative four vessel DSA of Case VI (A,B,), Left BA describing left P4 segment aneurysm

Figure 12 post operative (C, D, E, F) DSA showing embolized left P4 segment aneurysm with Onyx18 glue

Case VII: Male, 37 years of age, was admitted after sudden coma, after intubation CT scan revealed subarachnoid hemorrhage, suggested of aneurysm, DSA showed the left side of the P2, 3-segment fusiform aneurysm, managed by onyx embolization

Figure 13 Preoperative four vessels DSA of Case VII (A, B), Left BA describing left P2-3 segment fusiform aneurysm

Figure 14 microcathter angiography (C D E F) and post operative (G H I) DSA showing embolized left P2-3 segment fusiform aneurysm with coil and Onyx glue and good collateral.

5. DISCUSSION

Anatomic and Clinical Considerations of Cerebral Arteries

Anterior Cerebral Artery (ACA)

The anterior cerebral artery (ACA) is one of a pair of arteries on the brain that supplies oxygenated blood to most medial portions of the frontal lobes and superior medial parietal lobes [7]. The two anterior cerebral arteries arise from the internal carotid artery and are part of the Circle of Willis.The left and right anterior cerebral arteries are connected by the anterior communicating artery. The ACA is classified into 5 segments with the smaller branches from the ACA "callosal" arteries (supracallosal) considered as the A4 and A5 segments [8]. A1 segment originates from the internal carotid artery and extends to the anterior communicating artery (A Comm). The anteromedial central (medial lenticulostriate) arteries arise from this segment as well as the A Comm, which irrigate the caudate nucleus and the anterior limb of the internal capsule. A2 segment extends from the A Comm to the bifurcation forming the pericallosal and callosomarginal arteries. The recurrent artery of Heubner (distal medial striate artery), which irrigate the internal capsule, usually arises at the beginning of this segment near the AComm. 4 branches arise from this segment are orbito frontal artery (medial frontal basal) which arises first a small distance away from the AComm. The frontopolar artery (polar frontal), which arises after the orbitofrontal close to A2 when curves posteriorly over the corpus callosum which could also originate from the callosal marginal. A3 also termed the pericallosal artery this is one of (or the only) the main terminal branches of the ACA, which extends posteriorly in the pericallosal sulcus to form the internal parietal arteries (superior, inferior) and the precuneal artery. This artery may form an anastomosis with the posterior cerebral artery. Callosal marginal artery is commonly present terminal branch of the ACA, which bifurcates from the pericallosal artery. This artery in turn branches into the medial frontal arteries (Anterior, Intermediate, Posterior), and the paracentral artery, with the cingulate branches arising throughout its length. Depending on anatomical variation, the callosal marginal artery may be none discrete or not be visible. In the latter case, the branches mentioned will originate from the pericallosal artery [9, 10].

Posterior Fossa

In the posterior fossa, a wide variation in arterial distribution exists. Specific areas of the brain stem and cerebellum cannot always be predictably allotted to a particular cerebellar artery. The effects of occlusion of a cerebellar artery range from clinical silence to death, as a result of infarction of portions of brain stem or cerebellum [11]. Acute occlusion of any one of the cerebellar arteries is frequently associated with vomiting, dizziness, and inability to stand or walk. Recovery and survival of many patients after occlusion of a major cerebellar artery is attributed to adequacy of collateral circulation [12].In general, proximal occlusion of a cerebellar artery may result in a large ischemic area when collateral supply is insufficient, but with adequate collateral flow, no ischemia will occur at all. On the other hand, distal side brain occlusions have a higher probability of inducing ischemia, but the affected area will be limited.

POSTERIOR CEREBRAL ARTERY (PCA)

The posterior cerebral artery (PCA) is a branch of the internal carotid artery (ICA); the connection with the basilar artery (pars basilaris) develops later. The connection with the ICA (pars carotica) can completely regress or persist as a large or small vessel, becoming the posterior communicating artery (PComA) [13]. The PCA is divided into four segments: P1 is the segment proximal to the posterior communicating artery (PCoA); P2 extended from the PCoA to the posterior margin of the midbrain and is subdivided into an equal anterior (P2A) and posterior (P2P) half; P3 begins at the posterior midbrain, runs within the quadrigeminal cistern, and ends at the anterior limit of the calcarine fissure. The PCA had three types of branches: 1) cortical branches to the cerebrum; 2) central branches to the brain stem; and 3) ventricular branches to the choroid plexus. The largest branches reaching the lateral surface of the cerebrum can be located immediately anterior to the preoccipital notch, and in most can be seen in branches of the posterior temporal artery. The central branches are of two types: 1) direct perforating, and 2) circumferential. The direct perforating branches arise on P1 [13]. There are a series of small arteries arising from P2A and P2P rather than being a single vessel. The circumferential arteries usually arise from P1 and encircled the midbrain providing branches as far posteriorly as the colliculi. The branches to the choroid plexus are the medial and lateral posterior choroidal arteries; the former usually arises from P2A and enter the roof of the third ventricle, and the latter arises as a series of arteries from P2P and passes over the pulvinar to enter the lateral ventricle.

AICA

The AICA originates from the mid basilar artery, courses through the central part of the cerebellopontine angle, and encircles the pons near the abducent, facial, and vestibulocochlear nerves. After sending branches to the nerves entering the acoustic meatus and to the choroid plexus protruding from the foramen of Luschka, it passes around the flocculus on the middle cerebellar peduncle to supply the lips of the cerebellopontine fissure and the petrosal surface of the cerebellum. It commonly bifurcates near the facial-vestibulocochlear nerve complex to form a rostral and a caudal trunk. The AICA gives rise to perforating arteries to the brain stem, middle cerebellar peduncle, the choroid plexus, and arteries supplying the inner ear and the vestibulocochlear and facial nerves. Occlusion of the AICA results in syndromes related predominantly to the lateral portions of the brain stem and cerebellar peduncles, including palsies of the facial and vestibulocochlear nerves caused by involvement of the nerves and their nuclei. The most prominent symptom is vertigo, often associated with nausea and vomiting, followed by a facial paralysis, ipsilateral deafness, sensory loss, and cerebellar disorders. Patients can show nystagmus, ipsilateral loss of pain and temperature sensation on the face and corneal hypesthesia, Horner syndrome, cerebellar ataxia and asynergia, and an incomplete loss of pain and temperature sensation on the contralateral half of the body. All of the syndromes caused by its occlusion are not identical because of the variability of the AICA [12].

PICA

The PICA has the most variable course and area of supply of the cerebellar arteries. It arises from the vertebral artery near the inferior olive and passes posteriorly around the medulla. At the anterolateral margin of the medulla, it passes between the rootlets of the hypoglossal, glossopharyngeal, vagus, and accessory nerves. Then it courses around the cerebellar tonsil, enters the cerebellomedullary fissure (caudal loop), and passes posterior to the lower half of the roof of the fourth ventricle. On exiting the cerebellomedullary fissure (cranial loop), its branches are distributed to the vermis and to the suboccipital cerebellar surface. Most PICAs bifurcate into a medial and a lateral trunk. The medial trunk supplies the vermis and adjacent part of the hemisphere, and the lateral trunk supplies the cortical surface of the tonsil and the hemisphere. The proximal PICA gives off perforating medullary branches in its course around the medulla. The perforating arteries have numerous branches and anastomoses that create a plexiform pattern on the medullary surface. The consequences of a PICA occlusion vary and range from a clinically silent occlusion to infarction of portions of the brain stem or cerebellum, with swelling and tentorial herniation. The syndrome of occlusion of the PICA is referred to as the lateral medullary syndrome or Wallenberg syndrome and may include vomiting, dysphagia, dysarthria, hoarseness, ataxia, dizziness, vertigo, ipsilateral numbness of the face, loss of pain and temperature on the contra lateral half of the body, nystagmus, and ipsilateral Horner syndrome. Occlusion of the branches of the PICA distal to the medullary branches produces a syndrome resembling labyrinthitis and includes rotatorydizziness, nausea, vomiting, inability to stand or walk unaided, and nystagmus without appendicular dysmetria [12].

General Discussion

Distal aneurysms in the cerebral arteries are defined as outside the circle of Willis, on or beyond the A2 anterior cerebral artery, M2 middle cerebral artery, or P2 posterior cerebral segments. Distal aneurysms in the cerebellar arteries are on or beyond the s2 superior cerebellar artery, a2 anterior inferior cerebellar artery, or p2 posterior inferior cerebellar artery segments. Aneurysms of the cerebral arteries are rare and represented 0.8% of 2349 single bleeding aneurysms in the series presented by Locksley [14].Symptoms of brain aneurysms can be separated as ruptured cerebral aneurysm symptoms and unruptured cerebral aneurysm symptoms. In ruptured cerebral aneurysm symptoms are seen after the aneurysm ruptures, so called subarachnoid hemorrhage, people often complain of "the worst headache of their life."  Other ruptured cerebral aneurysm symptoms includes nausea and vomiting, stiff neck or neck pain, blurred vision or double vision, pain above and behind the eye, dilated pupils, sensitivity to light and loss of sensation while in unruptured cerebral aneurysm most aneurysms are asymptomatic particularly those ones which are small. Occasionally, large aneurysms may cause the symptoms related to pressure on the adjacent brain or nerves which includes peripheral vision deficits, thinking or processing problems, speech complications, perceptual problems, sudden changes in behavior, loss of balance and coordination, decreased concentration, short-term memory difficulty and fatigue. Because the symptoms of brain aneurysms can also be associated with other medical condition, diagnostic neuroradiology is regularly used to identify both ruptured and unruptured brain aneurysms. Distal aneurysms of cerebral arteries are rare lesions of all treated aneurysms in our practice. Similar low incidences have been reported previously. Most of our aneurysms presented with severe subarachnoid and intraventricular hemorrhage, and most patients were in poor clinical condition on admission, needing emergent intubation. Additional clinical symptoms on presentation may be explained by the intimate relation of cerebral arteries with the cranial nerves. Most aneurysms involved the circumference of the parent vessel. Although surgical treatment in experienced hands is associated with good results, access to the distal cerebral arteries may be challenging, needing destructive far-lateral trans-cochlear or translabyrinthine approaches [15-19]. Because most distal cerebral artery aneurysms involve the circumference of the small parent vessel, clipping with sparing of the parent artery is mostly impossible; this problem leaves trapping (with risk of ischemia) the only surgical option. In addition, surgery is often complicated by cranial nerve dysfunction, in view of the intimate relationship of the cerebellar arteries with cranial nerves III–XI [20-21]. In some cases, sophisticated surgical techniques such as hypothermic cardiac arrest and bypass surgery on distal cerebral arteries might require [21]. These techniques are not available in most neurosurgical centers. Because distal cerebral artery aneurysms are rare, not many surgeons will gain experience in the treatment of these aneurysms. In addition, most patients are in poor clinical condition and are not good surgical candidates in the acute phase. Although surgery for distal cerebral artery aneurysms is often difficult, limited to good-grade patients and associated with substantial morbidity, endovascular parent vessel occlusion is technically easy and can also be performed in the acute phase of hemorrhage in poor-grade patients. A substantial portion of distal cerebral artery aneurysms is located on a distal branch and not on the main stem, thereby limiting the area of possible induced infarction. In cases in which collateral circulation is insufficient, the area of infarction usually remains relatively restricted. Possible acute symptoms may have been masked by decreased levels of consciousness or cranial nerve dysfunction from the onset in critically ill patients in intensive care. Additional 3D angiography was valuable in evaluating the anatomy of the aneurysm and its relation with the parent vessel and in determining a working projection for catheterization with glue or coil occlusion. Our endovascular approach was effective in excluding the aneurysms from the circulation. Our follow-up protocol after parent vessel occlusion did not include follow-up angiography in all patients. Despite the fact that most patients were in poor clinical condition on admission, in 1 of 3 patients with a distal AICA aneurysm, central nerve VII and VIII palsy accompanied acute hemorrhage. In the remaining 2 patients, AICA occlusion did not induce dysfunction of these nerves. 3 0f 7 patients with distal MCA developed partial infraction, 2 0f 3 patients of PICA developed partial infraction and 1 0f 4 patient with distal ACA developed partial infraction .functional status on last follow-up was mainly determined by either cranial nerve dysfunction from the onset or cognition and memory disturbances as a result of subarachnoid and intraventricular hemorrhage and by the presence or extent of therapy-induced infarctions. Similar good outcomes after endovascular treatment of distal cerebral arteries have been reported in previous studies.

6. CONCLUSION

Distal cerebellar artery aneurysms are rare vascular disorders with an incidence in our practice of 1.3%. Most patients present with severe subarachnoid and intraventricular hemorrhage. Endovascular parent vessel occlusion is simple to perform and is effective in excluding the aneurysm from the circulation. In most patients, adequate collateral circulation prevents infarction in the territory of the occluded vessel. In this series, when infarction did occur, the clinical consequences were limited. Thus we see that distal aneurysms can be potentially fatal if not addressed in time, and that newer modalities of diagnosing and managing these cases have been a promising venture till now. Rarity of these lesions poses a problem in terms of greater number of research subjects. However the advent and refinement of interventional techniques have given us another very strong tool to handle these complex lesions, which in the past could only be dealt with by open surgery, thus requiring a lot of time and risking the patients to the surgical complications.

综述

Cerebral Aneurysms: Medical Imaging and recent advancements

Srijana Bista 综述 谢晓东 审校

Objective:

The objective of the study was to review the current trends including the types on intracranial aneurysms treatment. The advancement of neuroimaging techniques mostly used for diagnosis of intracranial aneurysms as well as neuroendovascular therapeutic options available is reviewed throughout the study.

Conclusion:

The diagnosis and management of intracranial aneurysms have evolved dramatically in the past 10 years. MR angiography and CT angiography allow radiologists to reliably and noninvasively diagnose most intracranial aneurysms. Nonoperative endovascular techniques for treating intracranial aneurysms are now making treatment increasingly safer and more effective.

Introduction:

An aneurysm occurs when part of a blood vessel swells. It may be either the blood vessel is damaged or there is a weakness in the wall of the blood vessel. As blood pressure builds up it balloons out at its damaged point. The swelling can be quite small or very large. When the blood vessels walls became it tends to extend along the blood vessel. As the aneurysm grows there is a greater risk of rupture which ultimately can lead to severe hemorrhage, and other complications like embolism/thrombosis, including sudden death or emergency management. An aneurysm may be present from birth (congenital) or it may develop later in life, such as after a blood vessel is injured during trauma or during any surgical procedure [1]. An aneurysm can occur in any part of the body. They tend to most commonly occur on the wall of the aorta - the large trunk artery that carries blood from the left ventricle of the heart to branch arteries. The aorta goes down through the chest and into the abdomen, where it divides into the iliac arteries (two branches). There are two main types of aneurysms:

1. Aortic aneurysm - occurs in the aorta. Can be abdominal or thoracic (higher up).

2. Cerebral aneurysm - occurs in an artery in the brain.

People of any age and either sex can have an aneurysm, although they are more common in men and people over 65 years of age. [2]

Classification of Aneurysms

True and false aneurysms

A true aneurysm is one that involves all three layers of the wall of an artery (intima, media and adventitia). True aneurysms include atherosclerotic, syphilitic, and congenital aneurysms, as well as ventricular aneurysms that follow transmural myocardial infarctions (aneurysms that involve all layers of the attenuated wall of the heart are also considered true aneurysms).[3] A false aneurysm or pseudo-aneurysm does not primarily involve such distortion of the vessel. It is a collection of blood leaking completely out of an artery or vein, but confined next to the vessel by the surrounding tissue. This blood-filled cavity wills eventually either thrombose (clot) enough to seal the leak or rupture out of the tougher tissue enclosing it and flow freely between layers of other tissues or into looser tissues. Pseudoaneurysms can be caused by trauma that punctures the artery and are a known complication of percutaneous arterial procedures, such as arteriography, arterial grafting, or use of an artery for injection. Like true aneurysms, they may be felt as an abnormal pulsatile mass on palpation.

Morphology of the Aneurysms

Aneurysms are classified by their macroscopic shape and size and are described as either saccular or fusiform. Saccular aneurysms are spherical in shape and involve only a portion of the vessel wall; they vary in size from 5 to 20 cm (8 in) in diameter, and are often filled, either partially or fully, by thrombus. Fusiform ("spindle-shaped") aneurysms are variable in both their diameter and length; their diameters can extend

up to 20 cm (8 in). They often involve large portions of the ascending and transverse aortic arch, the abdominal aorta, or less frequently the iliac arteries. The shape of an aneurysm is not pathognomonic for a specific disease.[4]

 Cerebral Aneurysms

A cerebral aneurysm is an abnormal bulging or ballooning of an intercerebral artery. The prevalence of cerebral aneurysms is in the range of 1-5%[5]。According to the National Institute of Neurological Disorders and Stroke (NINDS) of NIH, the incidence of reported ruptured aneurysms is about 10 per 100,000 persons per year (about 27,000 per year in the U.S.) [6] The vast majority of cerebral aneurysms form in the junction of arteries known as the Circle of Willis where arteries come together and from which these arteries send branches to different areas of the brain(Figure 1). Brain aneurysms can rupture and cause bleeding into your brain. This usually occurs in the area between your brain and the surrounding membrane (the arachnoid), called the subarachnoid space, causing a subarachnoid hemorrhage. Many small brain aneurysms, especially those located on the arteries in the front part of your brain, have a low risk of rupture. However, ruptured brain aneurysms can lead to stroke and other complications that can lead to severe disability and death. Hence early management is mandatory for good prognosis and treatment.

Medical Imaging Study

Imaging studies obtained in patients with cerebral aneurysms are becoming increasingly sophisticated. As a result, radiologists interpreting these studies are now in a unique position to better report relevant findings and make recommendations that may have significant impact on patient care. [7] It is important that radiologists interpreting such imaging studies become familiar with issues such as comparative specificity of imaging techniques, risk of aneurysm rupture, identification of high-risk populations and screening recommendations, and new endovascular methods used to treat aneurysms.

Most of the intracranial aneurysms are saccular (or so called berry) aneurysms and they may occur at predictable sites mostly around the circle of Willis. Unusual types of aneurysms are occasionally encountered, including dissecting, fusiform, serpentine, blood blister type, traumatic, mycotic (or infectious), atheromatous, and giant aneurysms, all of which may manifest with hemorrhage, thromboembolic events, or mass effect [8]

Approximately 85% of intracranial aneurysms are located around the ACA (anterior communicating artery),30–35%;, the PCA( posterior communicating artery),30–35%; the MCA( middle cerebral artery) bifurcation 20%;, the basilar artery (5%), the internal carotid artery (ICA) terminus or posterior wall, the superior cerebellar artery (SCA), or the posterior inferior cerebellar artery (PICA) [8]. Aneurysm size is traditionally reported as being small (< 15 mm), large (15–25 mm), giant (25–50 mm), and supergiant (> 50 mm). Most aneurysms encountered in practice belong in the first category, which has been further divided into the small (< 5 mm) and medium-sized (5–15 mm) subcategories [9]

The most serious presentation of intracranial aneurysms is subarachnoid hemorrhage (SAH). Despite improvements in diagnostic and therapeutic techniques, the mortality rate for SAH is relatively unchanged at approximately 50%. Fewer than 60% of survivors return to functional independent living [10] . The management of SAH relies heavily on sequential imaging to assess initial patient grade and follow patients through the approximately 2-week critical period when several complications may occur, e.g., re-hemorrhage, hydrocephalus, vasospasm, cerebral edema, and treatment complications.

Medical Imaging Techniques for assessing Cerebral Aneurysms

Computer Axial Tomography:Diagnosis of a ruptured cerebral aneurysm is commonly made by finding signs of subarachnoid hemorrhage(SAH)on a computed tomography (CT) scan. In ruptured aneurysms, CT reliably shows SAH because it relies on differences in electronic attenuation (Hounsfield Unit) between hyperdense acute hemorrhage and surrounding parenchyma

CTA (ComputerdTomography Angiography):

Computed tomography angiography (CTA) is an alternative to traditional angiography and can be performed without the need for arterial catheterization. This test combines a regular CT scan with a contrast dye injected into a vein. Once the dye is injected into a vein, it travels to the cerebral arteries, and images are created using a CT scan. These images show exactly how blood flows into the brain arteries. CT angiography (CTA) is performed on multi-detector row scanners using helical technology. Currently, 64-MDCT angiography has the ability to detect most intracranial aneurysms 3 mm or larger and allows evaluation of the osseous anatomy and 3D rendering of vessels, which most neurosurgeons find very helpful [11,12] Three basic techniques are available for the display of 3D CTA models: maximum intensity projection (MIP), which depicts the highest pixel value along the selected plane; surface shaded display (SSD), which shows the outer contour of the contrast column as an opaque surface; and the ray-sum projection, which displays the sum of pixel values along vectors projected through the model. SSD has been replaced by the volume-rendering technique in recent years[13]

When compared with digital subtraction angiography (DSA) as the reference standard, CTA has average reported specificity rates of 96–98% (90–94% for aneurysms smaller than 3 mm and up to 100% for aneurysms larger than 4 mm) and sensitivity rates of 96–98%[14] . With the advent of MDCT scanners with very high numbers of detectors (e.g., 256- and 320-MDCT scanners), further improvements in spatial resolution and accuracy are expected. CTA may also show ongoing extravasation of contrast material, indicating hemorrhage or rehemorrhage[15] (Fig.3). The limitations of CTA include lack of sensitivity for lesions involving the carotid artery at the skull base or within the contrast-filled cavernous sinuses. In addition, substantial concern has recently been raised regarding the high levels of radiation doses delivered to patients with CT, which is of concern in patients who need repeated imaging [16].

Magnetic Resonance Imaging and Magnetic Resonance Angiography

Similar to a CTA, MRA uses a magnetic field and pulses of radio wave energy to provide pictures of blood vessels inside the body. As with CTA and cerebral angiography, a dye is often used during MRA to make blood vessels show up more clearly. It has been used in recent few decades as a technique to detect aneurysms in patients (usually in the non-acute setting) with clinical features suspicious for the presence of an aneurysm or a family history of aneurysms [17] . Three-dimensional time-of-flight (TOF) MRA is the most widely accepted technique because it provides good spatial resolution, is relatively insensitive to signal loss caused by turbulent flow, and can be performed within a time span that allows anatomic MRI during the same imaging session. The spatial resolution of MRA at 1.5 T is on the order of 1 mm [18].

Digital Subtraction Angiography

During this investigation, a catheter is inserted through a blood vessel in the groin or arm and moved up through the vessel into the brain. A dye is then injected into the cerebral artery. As with the above tests, the dye allows any problems in the artery, including aneurysms, to be seen on the screen. Although this test is more invasive and carries more risk than the above tests, it is the best way to locate small (less than 5 mm) brain aneurysms.

In this procedure, iodinated contrast material (with the attendant risks of nephrotoxicity) and ionizing radiation is in use. It may also introduce the risk of complications related to the use of an arterial catheter, including stroke. Most experts continue to consider DSA the reference standard for evaluation of the intracranial circulation in general and for cerebral aneurysms (Figs. 4A and Fig 4B). In practice, if CTA is obtained as the initial study, the 3D rendering technique may prove useful in assisting with treatment planning [19,20]. One word of caution is that small intimal flaps (i.e., dissecting aneurysms or associated arterial dissections) may be missed, which is why the final analysis should rely on DSA. Novel developments in angiography equipment and postprocessing have provided additional capabilities that further enhance the role of DSA. For instance, 3D rotational angiography has increased the diagnostic capability of DSA.

Effective performance of DSA requires obtaining adequate planar projections to permit the most precise possible aneurysm measurements (neck-to-dome ratio, neck-to-artery ratio, and maximum dimensions). Analysis of aneurysm features, such as the relationship of aneurysms to surrounding structures, including perforating arteries, osseous structures, and the dural ring, is very important for facilitating surgical or endovascular treatment planning and allowing reliable follow-up comparison studies.

Cerebral aneurysm treatment: 

Surgical clipping:

In this treatment the aneurysm is closed off. The surgeon removes a section of the skull to get to the aneurysm and finds the blood vessel that feeds it. A tiny metal clip is placed on the neck of the aneurysm to block off the blood flow to it.

During the past three decades, there has been a general trend away from surgical clipping and toward less-invasive endovascular methods of treating aneurysms.  Also, there has been evolution in the less-invasive endovascular methods, from balloons in the aneurysm, to coils in the aneurysm, to stents in the parent vessel before insertion of coils into the aneurysm (sometimes called "stent-assisted coiling" or "jailing"), to specialized neurological stents that reconstruct the parent vessel to address the hemodynamic conditions that contributed to formation of the aneurysm in the first place. 

However, the most common methods of treating aneurysms are still surgical clipping (placing a clamp on the aneurysm from outside the vessel) and endovascular coiling (inserting flexible coils into the aneurysm from inside the vessel).  Limitations of clipping include: risks of invasive surgery; difficulty accessing aneurysms in some areas; difficulty clipping fusiform or wide-neck aneurysms; and failure to address parent vessel hemodynamics.  Limitations of coiling include: filling only a limited percentage of the aneurysm volume; coil compaction and recanalization over time; difficulty coiling fusiform or wide-neck aneurysms; prolapse of coils into the parent vessel; difficulty clipping later if needed; and failure to address parent vessel hemodynamics [21-26]. For these reasons, and as confirmed by the literature, there remains a significant unmet clinical need for development of new options to treat cerebral aneurysms.

Endovascular Coiling:

In this procedure, Endovascular coiling, a catheter is inserted, usually in the groin, and is threaded through the body to the brain where the aneurysm is located. A guide wire is used to push a soft platinum wire through the catheter and into the aneurysm. The wire coils up inside the aneurysm and disrupts the blood flow, making it clot. The clotting of the blood effectively seals off the aneurysm from the artery (Figure 5). Patients whose aneurysms are coiled instead of clipped have a better survival rate over five years, according to a long-term study of the International Subarachnoid Aneurysm Trial (ISAT). However, another study found that over time outcomes are similar.

Conclusion:

This review has highlighted the cranial aneurysms and the advances of medical imaging for assessment and treatment anticipating in the management of patients, treatment, and follow-up imaging. An understanding of current treatment regimens is important for radiologists because it provides familiarity with the types of devices they are likely to see on follow-up studies and enhances understanding of the goals of post-therapy imaging studies. DSA and cross-sectional imaging studies both play an important role in aneurysm detection for assessment of SAH as well as for screening purposes.