Aneurysm

A localized widening (dilatation) of an artery, vein, or the heart. At the area of an aneurysm, there is typically a bulge and the wall is weakened and may rupture. The word “aneurysm” comes from the Greek “aneurysma” meaning “a widening.”

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1. Circumscribed dilation of an artery or a cardiac chamber, a direct communication with the lumen, usually due to an acquired or congenital weakness of the wall of the artery or chamber. 2. Circumscribed dilation of a cardiac chamber usually due to an acquired or congenital weakness of the wall of the heart. [G. aneurysma (-mat-), a dilation, fr. eurys, wide]

- ampullary a. SYN: saccular a..

- a. by anastomosis a mass of dilated anastomosing vessels that produce a pulsating tumor usually in a superficial position.

- aortic a. diffuse or circumscribed dilation of a portion of the aorta ( e.g., abdominal aortic a., aortic arch a.. SEE ALSO: dissecting a..

- aortic sinus a. abnormal dilation of one or more of the three aortic sinuses situated behind the three aortic valve cusps.

- arteriosclerotic a. SYN: atherosclerotic a..

- arteriovenous a. 1. a dilated arteriovenous shunt; 2. communication between an artery and a vein, usually congenital or associated with atherosclerotic changes; more appropriately termed arteriovenous fistula or arteriovenous malformation.

- atherosclerotic a. the most common type of a., occurring in the abdominal aorta and other large arteries, primarily in the elderly. Often associated with atherosclerotic changes in blood vessel s in other parts of the body. SYN: arteriosclerotic a..

- axial a. an a. involving the entire circumference of a blood vessel.

- benign bone a. obsolete term for aneurysmal bone cyst.

- Bérard a. an arteriovenous a. in the tissues outside the injured vein.

- berry a. a small saccular a. of a cerebral artery that resembles a berry. Such aneurysms can rupture causing a subarachnoid hemorrhage.

- cardiac a. SYN: ventricular a..

- Charcot-Bouchard a. SYN: miliary a..

- cirsoid a. dilation of a group of blood vessel s owing to congenital malformation with arteriovenous shunting. SYN: cirsoid varix, racemose a., racemose hemangioma.

- compound a. an a. in which some of the coats of the artery are ruptured, others intact.

- congenital cerebral a. localized dilation of a cerebral vessel; usually a berry a..

- consecutive a. two or more aneurysms along the path of blood flow.

- coronary artery a. a. of the coronary artery, rarely congenital, usually due to atherosclerosis, inflammatory processes, or a coronary fistula.

- cylindroid a. SYN: tubular a..

- diffuse a. an a. that has enlarged and spread to the surrounding tissues as a consequence of rupture of its walls.

- dissecting a. condition resulting when blood passes from the true lumen of an artery into a false lumen within the arterial wall; layers of the wall are effectively split; most often due to necrosis of the medial layer, as in Marfan syndrome and with tear originating in the ascending (type A) or descending (type B) thoracic aorta or occasionally in smaller arteries such as the carotids; the false lumen may thrombose, rupture, re-enter the true lumen downstream, and/or shear off vital arterial branches; more properly termed aortic dissection rather than a. since the process is not transmural. SEE ALSO: aortic dissection.

- ductal a. a. of the patent ductus arteriosus, occurs either in infants or adults. SYN: ductus diverticulum.

- ectatic a. an a. in which all the coats of the artery, though stretched, are unruptured.

- false a. SYN: pseudoaneurysm.

- fusiform a. an elongated spindle-shaped dilation of an artery.

- hernial a. the protrusion of the stretched inner coats of an artery through a defect in the adventitia.

- infraclinoid a. an intracranial a. occurring below the level of the anterior clinoid process of the sphenoid bone.

- intracavernous a. an a. of the carotid artery within the cavernous sinus.

- intracranial a. any a. located within the cranium.

- miliary a. dilation in the diameter of small arteries and arterioles secondary to lipohyalinosis from long-standing hypertension; associated with intracerebral hematomas. SYN: Charcot-Bouchard a..

- mural a. SYN: ventricular a..

- mycotic a. an a. caused by the growth of fungi or bacteria within the vascular wall, usually following impaction of a septic embolus.

- Park a. an arteriovenous a. in which the brachial artery communicates with the brachial and median basilic veins.

- peripheral a. 1. a saclike a. springing from one side of an artery; 2. an a. of one of the smaller branches of an artery.

- phantom a. a palpable pulsating aorta, mistaken by novices for an a..

- Pott a. SYN: aneurysmal varix.

- pulmonary artery a. a. of the pulmonary artery; may be secondary to congenital valvular or infundibular stenosis; some are mycotic aneurysms (q.v.).

- racemose a. SYN: cirsoid a..

- Rasmussen a. aneurysmal dilation of a branch of a pulmonary artery in a tuberculous cavity, rupture of which may cause serious hemoptysis.

- a. of the right ventricle or right ventricular outflow patch a. occurring after right ventriculotomy; the a. may either be a false or a true a..

- ruptured a. an a. that is hemorrhaging into its wall or surrounding tissues.

- saccular a., sacculated a. a saclike bulging on one side of an artery. SYN: ampullary a..

- serpentine a. dilation and tortuosity of an artery, sometimes affecting the temporal, splenic, or iliac arteries in the elderly.

- a. of sinus of Valsalva a congenital thin-walled out pouching with an entirely intracardiac course, usually in the right or noncoronary sinus, that may rupture into the right, or rarely, the left heart chambers to form an aortocardiac fistula.

- supraclinoid a. an intracranial a. located immediately above the anterior clinoid process of the sphenoid bone.

- syphilitic a. an a., usually involving the thoracic aorta, resulting from tertiary syphilitic aortitis.

- traumatic a. an a. resulting from physical damage to the wall of an artery; usually a false a. or arteriovenous a..

- true a. localized dilation of an artery with an expanded lumen lined by stretched remnants of the arterial wall.

- tubular a. the uniform dilation of an artery along a considerable distance. SYN: cylindroid a..

- varicose a. a blood-containing sac, communicating with both an artery and a vein.

- ventricular a. thinning, stretching, and bulging of a weakened ventricular wall, usually as a result of myocardial infarction; rarely postinflammatory or congenital. SYN: cardiac a., mural a..

- a. of the ventricular portion of the membranous septum an a. that bulges toward the right in systole, often consisting of the anterior leaflet of the tricuspid valve.

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an·eu·rysm also an·eu·rism 'an-yə-.riz-əm n an abnormal blood-filled dilatation of a blood vessel and esp. an artery resulting from disease of the vessel wall

an·eu·rys·mal also an·eu·ris·mal .an-yə-'riz-məl adj

an·eu·rys·mal·ly -ē adv

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n.

a balloon-like swelling in the wall of an artery. This may be due to degenerative disease or infection, which damages the muscular coats of the vessel, or it may be the result of congenital deficiency in the muscular wall. An aortic aneurysm most frequently occurs in the abdominal aorta, below the level of the renal arteries. Beyond a certain size it is prone to rupture, presenting as an acute surgical emergency with abdominal and back pain and haemorrhagic shock. A dissecting aneurysm usually affects the first part of the aorta and results from a degenerative condition of its muscular coat. This weakness predisposes to a tear in the lining of the aorta, which allows blood to enter the wall and track along (dissect) the muscular coat. A dissecting aneurysm may rupture or it may compress the blood vessels arising from the aorta and produce infarction (localized necrosis) in the organs they supply. The patient complains of severe chest pain that has a tearing quality and often spreads to the back or abdomen. Surgical repair may help in some cases. A ventricular aneurysm may develop in the wall of the left ventricle after myocardial infarction. A segment of myocardium becomes replaced by scar tissue, which expands to form an aneurysmal sac. Heart failure may result or thrombosis within the aneurysm may act as a source of embolism. See also arteriovenous aneurysm.

Most aneurysms within the brain are congenital: there is a risk that they may burst, causing a subarachnoid haemorrhage. Berry aneurysms are small saccular aneurysms most commonly occurring in the branches of the circle of Willis. Usually associated with congenital weakness of the vessels, these aneurysms are a cause of fatal intracranial haemorrhage in young adults. Charcot-Bouchard aneurysms are small aneurysms found on tiny arteries within the brain of elderly and hypertensive subjects. These aneurysms may rupture, causing cerebral haemorrhage. Options for treatment of cerebral aneurysms include surgical clipping of the aneurysm and placing metallic coils within the aneurysm to establish a clot within it (endovascular coiling).

• aneurysmal adj.

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an·eu·rysm (anґu-riz″əm) [Gr. aneurysma a widening] a sac formed by the dilatation of the wall of an artery, a vein, or the heart; it is filled with fluid or clotted blood, often forming a pulsating tumor.