Aneurysm - aneurysm

A condition in which the arterial lumen expands in a localized manner, forming a lump. It is caused by partial weakness of the arterial wall and increased internal pressure. Based on their structure, they can be divided into true aneurysms, in which the entire thickness of the blood vessel wall is present in the aneurysm wall, and pseudoaneurysms, which lack the structure of the blood vessel wall due to a hematoma, and based on their shape, they can be divided into fusiform aneurysms and saccular aneurysms. When the media of the artery peels off in layers, blood enters between the layers through cracks in the intima, forming a two-cylinder aneurysm, this is called a dissecting aneurysm. Either type of aneurysm grows larger as it progresses, eventually rupturing and causing heavy bleeding.

Causes include congenital, syphilis, arteriosclerosis, cystic medial necrosis, bacterial infection, Behçet's disease, nonspecific vasculitis, and trauma. Aneurysms caused by congenital factors are common in intracranial arteries and can cause severe subarachnoid hemorrhage. Acquired aneurysms were once mostly caused by syphilis, but nowadays, arteriosclerosis is on the rise.

The most common site of aneurysm is the aorta, particularly the ascending thoracic aorta, the aortic arch, the descending thoracic aorta just below the origin of the left subclavian artery, and the abdominal aorta below the renal arteries. Dissecting aneurysms are overwhelmingly more common in the thoracic aorta, and are said to be caused by medial necrosis and arteriosclerosis associated with Marfan syndrome. Upper limb aneurysms, including the subclavian artery, are less common than lower limb aneurysms. In the lower limbs, popliteal artery aneurysms are more common. Carotid aneurysms are rare. Rarely, aneurysms are also seen in the coronary arteries, renal arteries, celiac arteries, and mesenteric arteries, but recently, coronary aneurysms caused by Kawasaki disease have been attracting attention. There have also been reports of infectious aneurysms secondary to sepsis and aneurysms associated with Behcet's disease.

Treatment varies depending on the location, but for intracranial aneurysms, the aneurysm wall is reinforced and the neck of the aneurysm is closed to prevent rupture. For aneurysms in other locations, surgery is performed to remove the affected area and replace it with a vascular graft, and the results of this surgery have improved significantly in recent years.

[Keiji Takeuchi]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

動脈内腔(ないくう)が限局性に瘤(こぶ)状に拡張した状態をいう。動脈壁の部分的脆弱(ぜいじゃく)と内圧の増加によって生じる。その構造からは、動脈瘤壁に血管壁の全層を有する真性動脈瘤と、血腫(けっしゅ)によるため血管壁の構造を欠く仮性動脈瘤に分けられ、その形状からは紡錘状動脈瘤や嚢(のう)状動脈瘤に分けられる。また、動脈の中膜が層状に剥離(はくり)して内膜の亀裂(きれつ)から血液が層間に入り二筒性になったものを、解離性動脈瘤という。いずれもその進展に伴い増大し、ついには破裂をきたし、大出血をもたらす。

　原因としては、先天性、梅毒、動脈硬化、嚢胞状中膜壊死(えし)、細菌感染、ベーチェット病、非特異性血管炎、外傷などがあげられる。先天性要因による動脈瘤は頭蓋(とうがい)内動脈に多く、重篤なくも膜下出血の原因となる。後天性のものは、かつては梅毒性のものが多かったが、現在では動脈硬化性のものが増加している。

　好発部位は大動脈で、とくに上行胸部大動脈、大動脈弓、左鎖骨下動脈起始部直下の下行胸部大動脈、腎(じん)動脈以下の腹部大動脈に多い。解離性動脈瘤は胸部の大動脈に圧倒的に多く、マルファン症候群に伴う中膜壊死や動脈硬化が原因といわれる。鎖骨下動脈を含む上肢動脈瘤は下肢動脈瘤に比べると頻度が少ない。下肢では膝窩(しっか)動脈瘤が多い。頸(けい)動脈瘤は少ない。まれに冠状動脈、腎動脈、腹腔動脈、腸間膜動脈などにもみられるが、最近、川崎病に起因した冠状動脈瘤が注目されている。また、敗血症に続発する感染性動脈瘤やベーチェット病に合併する動脈瘤の報告もある。

　治療は部位によって異なるが、頭蓋内動脈瘤では動脈瘤壁を補強したり動脈瘤の頸部を閉鎖して破裂を防ぐ。他部位の動脈瘤では患部を切除して代用血管と置換する手術が行われ、最近は手術成績が著しく向上している。

［竹内慶治］

出典　小学館　日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について　情報 | 凡例