Abdominal Aorta and Pelvic Arteries

Abdominal Aorta

The abdominal aorta begins at the level of the diaphragmatic crura and terminates at the bifurcation into the common iliac arteries. This bifurcation is usually in the vicinity of the L4-L5 disk interspace. The major blood supply to the abdominal viscera is derived from the aorta ( Fig. 10-1 ). The aorta is constant in location and presence, although there is extensive variability of the anatomy of the branch vessels. The average diameter of the abdominal aorta is 1.5-2 cm at the diaphragm and 1.5 cm below the renal arteries. The anterior branches of the abdominal aorta are the celiac, superior mesenteric (SMA), gonadal, phrenic, and inferior mesenteric arteries (IMA). The lateral branches are the renal and middle adrenal arteries ( Table 10-1 ). The posterior branches are the lumbar arteries (one pair for each lumbar vertebra) and the middle sacral artery (arising at the aortic bifurcation). Clinically, the abdominal aorta is divided into supra (above) and infra (below) renal artery segments. The impetus for this division is the higher incidence of atherosclerotic and aneurysmal disease in the infrarenal abdominal aorta, and the increased complexity of interventions that involve the suprarenal portion.

The anatomy of the testicular and ovarian arteries is similar in the abdomen, but divergent in the pelvis. In 70% of individuals, the gonadal arteries arise from the anterior surface of the abdominal aorta just below the renal arteries (see Fig. 10-1 ). The most common variant location for gonadal artery origins is the renal arteries (20%), followed by the adrenal, lumbar, or even iliac arteries. The gonadal arteries pass to the pelvis along the anterior surface of the psoas muscles, adjacent to the gonadal veins and the ureters, and anterior to the iliac vessels.

In the male pelvis, the testicular arteries have a lateral course, entering the spermatic cord to continue into the scrotum. These arteries are the sole blood supply to the testes. In the female pelvis, the ovarian arteries have a more medial path, through the suspensory ligament of the ovary. The ovarian artery provides branches to the ovary and fallopian tubes. The artery then continues medially to the uterus, where it anastomoses with the uterine artery in the broad ligament.

The lumbar arteries are paired vessels that arise from the posterior wall of the abdominal aorta at the levels of the lumbar vertebrae. The origins of the paired lumbar arteries may be separate, or conjoint. These vessels anastomose with the intercostal and other chest wall arteries superiorly, the epigastric arteries anteriorly, and the internal iliac arteries inferiorly. These anastomoses can form the basis of collateral supply to the lower extremities in cases of distal aortic occlusive disease. The lumbar arteries supply the musculature of the back and abdominal wall, as well as the branches to the vertebral bodies and the contents of the spinal canal. This is of paramount concern whenever embolization of a lumbar artery for a nonneurologic indication is contemplated. In a small percentage of patients, the lower anterior spinal artery (artery of Adamkiewicz) will arise from an L1 or L2 lumbar artery.

The median sacral artery arises from the posterior wall of the aorta just proximal to the aortic bifurcation or as a common trunk with the L5 lumbar arteries (see Fig. 10-1 ). Occasionally, the median sacral artery will arise from a common iliac artery. This artery maintains a midline course in the pelvis, providing branches to the sacrum and coccyx. The median sacral artery is distinguished angiographically from the superior hemorrhoidal branch of the IMA by its posterior location and lack of a terminal bifurcation. The median sacral artery branches often anastomose with iliolumbar and rectal arteries.

Iliac Arteries and Their Branches

The aorta usually bifurcates between the L3-4 and L4-5 disk space into the right and left common iliac arteries ( Fig. 10-2 ; see Fig. 10-1 ). In 2% of patients, the aorta divides over the L3 vertebral body, resulting in a steep bifurcation that is challenging to cross angiographically. The common iliac arteries are symmetric structures that usually have no major side-branches. In the adult, the average common iliac artery is 8-10 mm in diameter and 3-6 cm in length. The course of the artery is caudal, lateral, and slightly posterior into the pelvis. The right common iliac artery lies anterior and across the left common iliac vein. If seen, a small branch arising from a common iliac artery and taking a superior course into the abdomen will most likely be an accessory lower pole renal artery. Occasionally, a median sacral artery may arise from a common iliac artery.

The common iliac arteries terminate when they bifurcate into the internal and external iliac arteries. The bifurcation is a point of fixation of the iliac arteries in the pelvis. The internal iliac (also known as the hypogastric ) artery originates posterior and medial from the common iliac artery. This vessel is 1-4 cm in length, traveling in a posterior and inferior direction into the bony pelvis. The internal iliac artery then bifurcates into an anterior and posterior division (see Fig. 10-2 ). The divisional arteries then give rise to the major visceral and muscular arteries of the pelvis ( Box 10-1 ). There is great variation in the branching patterns of the pelvic arteries. When these variants are encountered, identification of vessels should be based on what they supply rather than their point of origin.

The branches of the posterior division are the iliolumbar, superior gluteal, and lateral sacral arteries. The iliolumbar artery is usually the first branch, although it may arise from the proximal internal iliac or, rarely, the common iliac artery. The iliolumbar artery courses superiorly along the sacroiliac joint. There is usually an anastomosis between this artery and the lowest lumbar artery. The superior gluteal artery is the largest component of the posterior division. This artery exits the bony pelvis through the greater sciatic foramen, superior to the piriformis muscle, to supply the muscles of the posterior pelvis. The lateral sacral arteries are named for their origins relative to the sacrum, rather than their course in the pelvis. These arteries are small in caliber and frequently multiple. They travel medially toward the sacrum, with anastomoses to the median sacral artery and the opposite lateral sacral vessels.

The anterior division of the hypogastric artery supplies the visceral and muscular contents of the pelvic cavity. The visceral branches are the internal pudendal, vesicle, middle rectal, and in females, the uterine and vaginal arteries ( Fig. 10-3 ; see Fig. 10-2 ). Discrete superior and inferior vesicle arteries are usually present. In females, the inferior vesicle artery becomes one of the vaginal arteries. The middle rectal artery, frequently a branch of the inferior vesicle artery, anastomoses with the IMA through the superior hemorrhoidal artery. The uterine artery courses medially in the broad ligament superior to the ureter. At the uterus the artery assumes a characteristic corkscrew configuration as it travels parallel to the uterine body. The uterus is a very vascular organ that stains or enhances intensely at angiography, particularly in premenopausal women. The uterine arteries anastomose with both the ovarian artery and the vaginal arteries. The internal pudendal artery supplies the external genitalia. Accessory pudendal branches may arise from other anterior division arteries or from external iliac artery branches. The internal pudendal artery exits the floor of the pelvis between the piriformis and coccygeus muscles, after which it travels anteriorly along the lateral border of the pelvis. The inferior rectal artery arises as a branch of the internal pudendal in this region. In males, the internal pudendal artery bifurcates into the perineal artery (to the scrotum) and a common penile artery ( Fig. 10-4 ). The common penile artery bifurcates into deep penile (in the center of the corpus cavernosum) and dorsal penile (along the dorsal surface of the corpus cavernosum) arteries as it travels beneath the pubic symphysis. The prostatic artery arises as branch of the internal pudendal artery in about 50% of men, as a discrete branch of the anterior division in approximately 25%, and as branches of the obturator or inferior gluteal artery in the remainder. The prostatic artery often gives rise to branches to the bladder and seminal vesicles. At the prostate the artery usually bifurcates into posterior and anterior capsular arteries. In 25% of males, the anterior capsular artery anastomoses with distal branches of the internal pudendal artery. In females, the internal pudendal artery supplies the labia and the clitoris.

The obturator and inferior gluteal arteries are the primary musculoskeletal branches of the anterior division of the internal iliac artery (see Fig. 10-2 ). Both vessels frequently provide branches to the bladder. The obturator artery arises from the anterior division in 50% of individuals. This vessel exits the pelvis through the obturator canal, where it has a characteristic bifurcation. In approximately 15% of people, the artery may take its origin from the inferior gluteal or the internal pudendal arteries. The obturator artery arises from the superior gluteal artery (a branch of the posterior division) in 20% of individuals and from the common femoral or inferior epigastric arteries in 20%. The inferior gluteal artery is a branch of the anterior division in 75% of individuals and of the posterior division in 25%. The artery exits the pelvis between the piriformis and the coccygeus muscles in the lower portion of the sciatic notch. The inferior gluteal artery accompanies the sciatic and posterior femoral cutaneous nerves, terminating in branches to the buttocks and posterior thigh.

The external iliac arteries provide blood supply to the lower extremities. The typical diameter of the external iliac artery is 5-7 mm. The artery angles anteriorly and laterally from the common iliac artery bifurcation, passing under the inguinal ligament to form the common femoral artery. The angulation between the common and external iliac arteries can become severe in patients with redundant atherosclerotic arteries. The only branches of the external iliac artery are usually the circumflex iliac arteries (deep and superficial) arising laterally, and the inferior epigastric artery medially (see Fig. 10-1 ). These branches demarcate the transition from the external iliac to common femoral arteries. As noted above, the obturator artery is replaced to the external iliac artery in 20% of individuals, usually arising from a common trunk with the inferior epigastric artery.