Angle of Louis Landmarks

The angle of louis is the angle formed at the sternomanubrial joint between the manubrium and the sternum.  It is found at the 2nd costal cartilage level and denotes the level of the:

• aortic arch
• carina (trachea bifurcation)
• t4/t5 disc

Falciform Ligament

The falciform ligament is a ligament that attaches the liver to the anterior body wall.

It is composed of 2 layers of peritoneum attached closely together.

Retroperitoneal Space

The retroperitoneal space is the anatomical space behind the peritoneum. Organs are retroperitoneal if only their anterior surface has peritoneum.

A useful mnemonic to aid recollection of the abdominal retroperitoneal viscera is SAD PUCKER:

• S = Suprarenal glands (aka the adrenal glands)
• A = Aorta/IVC
• D = Duodenum (second and third segments [some also include the fourth segment] )
• P = Pancreas (tail is intraperitoneal)
• U = Ureters
• C = Colon (only the ascending and descending parts)
• K = Kidneys
• E = Esophagus
• R = Rectum

Peritoneum

The peritoneum is a serous membrane that forms the lining of the abdominal cavity. It supports the organs and serves as a conduit for their blood and lymph vessels and nerves.

The anterior layer of the peritoneum (on the abdominal wall) is the parietal peritoneum. The inside layer of peritoneum that surrounds the organs is the visceral peritoneum. Between these 2 layers is the peritoneal cavity.

Extended Branching of the Abdominal Aorta

1. inferior phrenic a.
2. celiac a.
   1. left gastric a.
   2. splenic a.
      1. short gastric arteries (6)
      2. splenic arteries (6)
      3. left gastroepiploic a.
   3. hepatic a.
      1. cystic a.
      2. right gastric a.
      3. gastroduodenal a.
         1. right gastroepiploic a.
         2. superior pancreaticoduodenal a.
      4. right hepatic a.
      5. left hepatic a.

1. superior mesenteric a.
   1. jejunal and ileal arteries
   2. inferior pancreaticoduodenal a.
   3. middle colic a.
   4. right colic a.
   5. ileocolic a
      1. anterior cecal a.
      2. posterior cecal a. – appendicular a.
      3. ileal a.
      4. colic a.

1. middle suprarenal a.
2. renal a.
3. testicular or ovarian a.

1. four lumbar arteries

1. inferior mesenteric a.
   1. left colic a.
   2. sigmoid arteries (2 or 3)
   3. superior rectal a.

1. median sacral a.

1. 1. external iliac a.
   2. internal iliac a.

Abdominal Aorta

The abdominal aorta is a direct continuation of the descending aorta. It is just medial to the IVC. The AA has 10 branches:

1. inferior phrenic
2. celiac
3. superior mesenteric
4. middle suprarenal
5. renal
6. gonadal
7. lumbar
8. inferior mesenteric
9. median sacral
10. common iliac

Arcuate Line

The arcuate line marks the lower limit of the posterior layer of the rectus sheath. Superior to the line, the rectus sheath splits into a anterior and posterior section, with the rectus abdominus muscles lying between the 2 sections.

Rectus Sheath

The rectus sheath is formed by the aponeuroses of the internal and external abdominal oblique muscles and the transverse oblique muscle. It contains the rectus abdominus and pyrimidalis muscles. It can be divided into the anterior and posterior laminae. The arrangement of the layers of the rectus sheath is different at different points in the body. This difference is illustrated in the image below:

Blood Supply of the Abdominal Wall

The abdominal wall is supplied by the follow arteries:

1. superior epigastric artery
2. inferior epigastric artery
3. lumbar arteries
4. deep circumflex iliac

Note: the inferior epigastric artery runs superiorly on the transversalis fascia and enters the arcuate line to gain the rectus sheath. 

Note: the superior epigastric artery enters the rectus sheath superiorly just inferior to the 7th costal cartilage.

Thoracoabdominal Nerves

These nerves are the ventral rami of the thoracic spinal nerves T7-T11 and subcostal nerves T12. They supply the anterolateral muscles and overlying skin. These nerves are supplemented by the anterior terminal branches of the subcostal nerves and by a branch of the iliohypogastric nerve (L1) of the lumbar plexus after passing through the muscles, they are sensory nerves of the skin.