A line between the anterior superior iliac spine and the pubic tubercle marks the position of the inguinal ligament, which separates the anterior abdominal wall above from the thigh of the lower limb below.
The iliac crest separates the posterolateral abdominal wall from the gluteal region of the lower limb.
The upper part of the abdominal cavity projects above the costal margin to the diaphragm, and therefore abdominal viscera in this region of the abdomen are protected by the thoracic wall.
The level of the diaphragm varies during the breathing cycle. The dome of the diaphragm on the right can reach as high as the fourth costal cartilage during forced expiration.
How to find the superficial inguinal ring
The superficial inguinal ring is an elongate triangular defect in the aponeurosis of the external oblique (Fig. 4.177). It lies in the lower medial aspect of the anterior abdominal wall and is the external opening of the inguinal canal. The inguinal canal and superficial ring are larger in men than in women:
In men, structures that pass between the abdomen and the testis pass through the inguinal canal and superficial inguinal ring.
In women, the round ligament of the uterus passes through the inguinal canal and superficial inguinal ring to merge with connective tissue of the labium majus.
The superficial inguinal ring is superior to the pubic crest and tubercle and to the medial end of the inguinal ligament:
In men, the superficial inguinal ring can be easily located by following the spermatic cord superiorly to the lower abdominal wall—the external spermatic fascia of the spermatic cord is continuous with the margins of the superficial inguinal ring.
In women, the pubic tubercle can be palpated and the ring is superior and lateral to it.
The deep inguinal ring, which is the internal opening to the inguinal canal, lies superior to the inguinal ligament, midway between the anterior superior iliac spine and pubic symphysis. The pulse of the femoral artery can be felt in the same position but below the inguinal ligament.
Because the superficial inguinal ring is the site where inguinal hernias appear, particularly in men, the ring and related parts of the inguinal canal are often evaluated during physical examination.
How to determine lumbar vertebral levels
Lumbar vertebral levels are useful for visualizing the positions of viscera and major blood vessels. The approximate positions of the lumbar vertebrae can be established using palpable or visible landmarks (Fig. 4.178):
A horizontal plane passes through the medial ends of the ninth costal cartilages and the body of the LI vertebra—this transpyloric plane cuts through the body midway between the suprasternal (jugular) notch and the pubic symphysis.
A horizontal plane passes through the lower edge of the costal margin (tenth costal cartilage) and the body of the LIII vertebra—the umbilicus is normally on a horizontal plane that passes through the disc between the LIII and LIV vertebrae.
A horizontal plane (supracristal plane) through the highest point on the iliac crest passes through the spine and body of the LIV vertebra;
A plane through the tubercles of the crest of the ilium passes through the body of the LV vertebra.
Visualizing structures at the LI
The LI vertebral level is marked by the transpyloric plane, which cuts transversely through the body midway between the jugular notch and pubic symphysis, and through the ends of the ninth costal cartilages (Fig. 4.179). At this level are: the beginning and upper limit of the end of the duodenum, the hila of the kidneys, the neck of the pancreas, and the origin of the superior mesenteric artery from the aorta.
The left and right colic flexures also are close to this level.
Visualizing the position of major
Each of the vertebral levels in the abdomen is related to the origin of major blood vessels (Fig. 4.180):