Spleen

I. ANATOMY AND FUNCTION (Figure 11-1)

A. Anatomy. The spleen is located in the left hypochondriac region, anterior to ribs 9, 10, and 11. This location puts the spleen in jeopardy in the case of rib fractures. The spleen does not extend below the costal margin, so it is not easily palpable unless splenomegaly (i.e., an enlarged spleen) is present. The spleen is palpated with the patient in a right lateral decubitus position with the leg flexed. It is attached to the stomach by the gastrosplenic ligament, which contains the short gastric arteries and veins and the left gastroepiploic artery and vein. It is attached to the kidney by the splenorenal ligament, which contains the five terminal branches of the splenic artery, tributaries of the splenic vein, and the tail of the pancreas. Accessory spleens are found in 20% of the population. They usually are located near the hilum, the tail of the pancreas, or within the gastrosplenic ligament.

B. Functions of the spleen include: removal of old or abnormal red blood cells (RBCs); removal of inclusion bodies from RBCs (e.g., Howell-Jolly bodies (nuclear remnants), Pappenheimer bodies (iron granules), or Heinz bodies (denatured hemoglobin)); removal of poorly opsonized pathogens; production of immunoglobulin (Ig) M by plasma cells; storage of platelets; and protection from infection.

C. The arterial supply is from the splenic artery (the largest branch of the celiac trunk). The splenic artery has the following branches: dorsal pancreatic artery, great pancreatic artery, caudal pancreatic arteries, short gastric arteries, and left gastroepiploic artery, and ends with five terminal branches. These terminal branches of the splenic artery supply individual segments of the spleen, and there are no anastomoses between them (i.e., they are end arteries). Obstruction or ligation of any terminal branch results in splenic infarction (i.e., the spleen is very prone to infarction). Splenic artery aneurysms are particularly likely to rupture in pregnant women, so these aneurysms should be resected when present in women of childbearing age.

D. Venous drainage is to the splenic vein. The splenic vein joins the superior mesenteric vein to form the portal vein. The inferior mesenteric vein usually joins the splenic vein (see Chapter 8 III).

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