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Abdominal Aortic Coarctation and Hypoplasia
Focal developmental narrowings of the distal thoracic and abdominal aorta are rare anomalies accounting for less than 2% of all aortic coarctations. Most physicians have limited experience with the management of these unusual lesions. Abdominal aortic coarctations are categorized by the most superior extent of the aortic narrowing. Among these aortic coarctations, 69% are suprarenal ( Figure 1 ). Narrowings originating in the intrarenal aorta occur in 23% of patients ( Figure 2 ) and in the infrarenal aorta in 8% of patients ( Figure 3 ). Diffuse involvement of the entire abdominal aorta is usually classified in the suprarenal category ( Figure 4 ).
A, Suprarenal abdominal aortic coarctation (bracket) with superior mesenteric artery stenosis (arrow). B, Bilateral renal artery ostial stenosis (arrows). Note common trunk of lower lumbar artery (arrow). Preoperative computed tomography angiography, anterior and posterior projections, respectively.
(From Stanley JC, Criado E, Eliason JL, et al: Abdominal aortic coarctation: Surgical treatment of 53 patients with a thoracoabdominal bypass, patch aortoplasty, or interposition aortoaortic graft, J Vasc Surg 48:1073–1082, 2008).
Intrarenal abdominal aortic coarctation with bilateral artery stenosis ). Preoperative aortogram.
(From Stanley JC, Criado E, Eliason JL, et al: Abdominal aortic coarctation: Surgical treatment of 53 patients with a thoracoabdominal bypass, patch aortoplasty, or interposition aortoaortic graft, J Vasc Surg 48:1073–1082, 2008).
Infrarenal abdominal aortic coarctation (arrows).
(From Stanley JC, Wakefield TW: Arterial fibroplasia. In Rutherford RB (ed): Vascular surgery , 3rd ed, Philadelphia, 1989, WB Saunders, pp 245–265.)
Diffuse aortic hypoplasia extending from the level of the celiac artery to the infrarenal aorta. Severe renal arterial occlusive disease is most apparent, affecting the ostial of two left renal arteries.
(From Graham LM, Zelenock GB, Erlandson EE, et al: Abdominal aortic coarctation and segmental hypoplasia, Surgery 86:519–529, 1979; with permission).
Aortoiliac hypoplasia occurs in a distinct subgroup of patients, mostly younger women, with atherosclerosis often affecting the narrowed aorta and iliac arteries. In fact, approximately 2% of women with arteriosclerotic aortoiliac occlusive disease manifest this entity. Regardless of the particular nomenclature used, most evidence suggests that both aortic coarctation and aortoiliac hypoplasia represent a spectrum of developmental abnormalities. Variations in their clinical presentation relate more to different anatomic locations and secondary pathologic events than the underlying etiologic differences. An exception exists with aortic narrowings caused by an inflammatory aortoarteritis such as occurs in Takayasu’s syndrome, in which other systemic manifestations may be more prominent than the vascular symptoms.
Etiology
The most widely accepted hypothesis as to the cause of the developmental narrowings relates to abnormal fetal events, including faulty fusion of the two primitive dorsal aortas during intrauterine life. Indirect evidence in support of this is derived from the fact that multiple renal arteries occur in 70% of patients with narrowings of the midabdominal aorta. This is two to three times the expected incidence of multiple renal arteries in the general population. The basis for this is complex.
During normal development in most embryos, fusion of the paired dorsal aortas occurs simultaneously with regression of all but one dominant metanephric vessel to each kidney around day 25 of embryonic life. It is speculated that development of a single renal artery to each kidney occurs because of its obligate hemodynamic advantage over adjacent metanephric vessels. By creating local blood flow disturbances with an aortic fusion abnormality, this obligate hemodynamic advantage is lost and additional metanephric channels persist. Support for an overfusion of the two aortas comes from the finding of a single bifurcating distal lumbar artery in up to 55% of patients with abdominal aortic coarctations and aortoiliac hypoplasia (see Figure 1 ), compared to less than 5% in normal persons. Multiple renal arteries are less likely to develop when the aortic coarctation is distant from the central abdominal aorta.
Theoretically, any event that alters the normal transition or organization of fetal mesenchymal cells into vascular smooth muscle can result in narrowing of the aorta as well as splanchnic and renal arterial stenoses. This might explain the existence of aortic coarctation or hypoplasia following cytocidal viral infections such as gestational rubella. A genetic alteration in the growth and development of vascular smooth muscle has also been implicated in abdominal aortic coarctation and hypoplasia associated with neurofibromatosis 1 and Williams syndrome. Coincident with the aortic narrowings in patients with Williams syndrome are the common occurrence of renal and splanchnic arterial narrowings. These arteries at their aortic origins are truly diminutive. It is more than happenstance that among our patients with midabdominal aortic narrowings, renal arterial stenoses were seen in 87% and splanchnic arterial occlusive disease in 62%.
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