The word "aneurysm" comes from the Greek word aneurysma (ana meaning across, and eurys meaning broad) and denotes an abnormal dilatation of an artery. Cerebral aneurysms involve both the anterior circulation and the posterior, or vertebrobasilar, circulation. Anterior circulation aneurysms arise from the internal carotid artery or any of its branches, whereas posterior circulation aneurysms arise from the vertebral artery, basilar artery, or any of their branches.
Intracranial aneurysms are named according to the artery and/or segment of origin; for example, anterior communicating aneurysms arise from the anterior communicating artery, and posterior communicating artery aneurysms arise from the internal carotid artery near the origin of the posterior communicating artery. Intracranial aneurysms are classified into saccular and nonsaccular types, according to their shape and etiology. Nonsaccular aneurysms include atherosclerotic, fusiform, traumatic, and mycotic types. Saccular, or berry, aneurysms have several anatomic characteristics that distinguish them from other types of intracranial aneurysms. Typically, saccular aneurysms arise at a bifurcation or along a curve of the parent vessel, or they point in the direction in which flow would proceed if the curve were not present
Several theories attempt to explain the origin of intracranial aneurysms. Initially, a defect in the internal elastic lamina of arterial walls was postulated as the mechanism responsible for the genesis of saccular, intracranial aneurysms; however, numerous histologic and experimental studies have failed to reveal evidence that supports this theory. Currently, the most important pathogenetic factor in aneurysmal formation is considered to be an area of mural degeneration in regions of hemodynamic stress.
Many risk factors are correlated with the development of intracranial aneurysms and related aneurysmal subarachnoid hemorrhage (SAH). These factors include arterial hypertension, cigarette smoking, female ***, use of analgesics, and a genetic predisposition. Patients with connective tissue disorders, such as Marfan syndrome, Ehlers-Danlos syndrome, polycystic kidney disease, coarctation of the aorta, and intracranial arteriovenous malformations, have an increased incidence of intracranial aneurysms.
The internal carotid artery enters the petrous portion of the temporal bone at the base of the skull through the carotid canal. Within the petrous bone, the carotid artery courses vertically and then turns horizontally at its genu to travel in an anteromedial direction, forming the carotid siphon. As the carotid artery passes above the foramen lacerum and under the gasserian ganglion, it penetrates the lateral dural ring and turns medially, forming the lateral carotid loop, to enter the cavernous sinus. In the cavernous sinus (ie, the cavernous segment), the carotid artery proceeds in a superomedial direction toward the posterior clinoid process. At the level of the posterior clinoid, the carotid artery turns forward, forming the medial loop. The meningohypophyseal trunk originates at this level. The carotid then exits the cavernous sinus and enters the subarachnoid space.
The ophthalmic segment of the internal carotid artery extends from the distal dural ring to the origin of the posterior communicating artery. This is the longest subarachnoid segment of the internal carotid artery, and it possesses 2 major bends that create areas of hemodynamic stress that predispose it to Aneurysm formation. The first bend, best depicted on lateral angiographic views, occurs as the carotid artery ascends and bends sharply in a posterior direction after it penetrates the dura. The second bend, best appreciated on a dorsal or anteroposterior angiographic view, is a gentler medial-to-lateral curve that occurs as the artery courses medial to the anterior clinoid process and laterally arcs to ascend toward the bifurcation.
The ophthalmic segment has 2 major branches: the ophthalmic artery and the superior hypophyseal artery. The ophthalmic artery usually arises immediately beneath the optic nerve, and the superior hypophyseal artery arises from the medial or ventromedial surface of the carotid, below the anterior clinoid process. Ophthalmic aneurysms typically arise along the first bend of the internal carotid artery, distal to the origin of the ophthalmic artery, and project either dorsally or dorsomedially toward the optic nerve. Superior hypophyseal artery aneurysms usually arise from the inferomedial surface of the internal carotid artery and project superomedially. The posterior communicating artery originates from the posteromedial surface of the internal carotid artery and penetrates the membrane of Liliequist to join the posterior cerebral artery inside the interpeduncular cistern.
Several perforators originate from the carotid or posterior communicating artery — namely, the anterior thalamoperforating arteries. Posterior communicating aneurysms project posteriorly and slightly inferiorly.
The choroidal segment of the internal carotid artery begins at the origin of the anterior choroidal artery and ends at the carotid bifurcation. The anterior choroidal artery arises distal and lateral to the posterior communicating artery. The internal carotid artery then bifurcates into the anterior and middle cerebral arteries.
The middle cerebral artery begins at the bifurcation of the internal carotid artery and courses along the sylvian fissure. It can be divided into the following 4 segments: (1) an M1 segment located between the carotid bifurcation and the genu, (2) an M2 segment that courses over the insular surface, (3) an M3 segment that traverses the opercular surface of the sylvian fissure to reach the cortical surface, and (4) a distal M4 segment consisting of its cortical branches.
The vertebral artery enters the subarachnoid space at the cranio-occipital junction. The first branch is the posterior spinal artery, which descends into the spinal cord. The vertebral artery then courses medially and superiorly around the medulla. The most important branch is the posterior inferior cerebellar artery, which travels in a posterolateral direction, just inferior to the oliva.
The basilar artery begins at the vertebrobasilar junction and courses superiorly toward the interpeduncular fossa. The first major branch of the basilar artery is the anterior inferior cerebellar artery, which courses laterally and posteriorly to supply the inferior surface of the cerebellum. The superior cerebellar artery originates just proximal to the basilar bifurcation and courses laterally to supply the superior cerebellar hemisphere. The basilar artery terminates in the interpeduncular fossa, where it bifurcates into the posterior cerebral arteries.
The posterior cerebral artery consists of 3 segments: (1) the P1 segment, which extends from its origin at the basilar bifurcation to its junction with the posterior communicating artery and contains several posterior thalamoperforating arteries; (2) the P2 segment, which courses through the crural and ambient cisterns, serving as the origin of the anterior temporal, hippocampal, medial posterior choroidal, peduncular perforating, middle temporal, posterior temporal, and lateral posterior choroidal arteries; and (3) the P3 segment, which courses through the quadrigeminal cistern toward the calcarine fissure, where it divides into calcarine and parieto-occipital arteries.
A strong clinical suspicion of aneurysm can be validated by using several diagnostic studies, including CT, lumbar puncture, magnetic resonance imaging (MRI), and cerebral angiography. CT is typically the first diagnostic test ordered when the possibility of SAH exists. Findings on a nonenhanced CT scan can confirm subarachnoid blood in more than 90% of patients with acute SAH. Diffuse, severe SAH is seldom helpful in suggesting the specific site of the aneurysm. Localized SAH, however, can be highly indicative of the site of aneurysm rupture, as in the case of blood in the sylvian fissure caused by a rupture of a middle cerebral artery (MCA) trifurcation aneurysm or in the presence of interhemispheric blood between the anterior part of the frontal lobes caused by the rupture of an aneurysm of the anterior communicating artery.
T1-weighted magnetic resonance image (MRI) of a middle-aged woman with progressive headaches, aphasia, and right-sided hemiparesis. A large intracerebral mass with a significant amount of surrounding edema is depicted. The lesion is a giant internal carotid artery aneurysm.
Left oblique cerebral angiogram in a patient with multiple intracranial aneurysms shows an anterior communicating aneurysm and a middle cerebral artery aneurysm. The patient underwent a frontotemporoparietal craniotomy, during which surgical clips were placed in both lesions in one setting.
Nonenhanced CT scan of a middle-aged man with headaches. The patient had a giant aneurysm of the left internal carotid artery in its intracavernous segment. This aneurysm is densely calcified and is easily depicted.
[align=justify][glow=FFFF00]مجهود رائع[/glow][/align] بس تمنيت يكون بالغه العربيه عشان الفائده تكون للجميع
thanks for you
I prefer this topic with arabic
to understanding all pepole[/align]
حبيت يكون الموضوع علمي بحت و بالغة الانجليزيه عشاان نستفيد اكثر من الموضوع ومن اللغة
لكن ولا يهمكم المره الجايه راح اجعل المواضيع مترجمه ولكن بالغة الانجليزيه
لو كان باللغة العربية لتعم الفائده
thanks for you
وتقبل تيحات محبكم بالله............. اخوكم سعد1010 [/align]
ان شااء الله
في المرات القادمه راح يكون بالغة العربيه
مشرف ملتقى التصوير الطبي ( الأشعة )
[[moveo=up]right]thankyou very much
specilist in radaiology/][/moveo]
حبيت اشارك بحالة سويتها عام 2007 بس محتفض بالصور الى الان
على جهاز GE 64 VCT
with and without bone
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