Spleen

Spleen Overview

• The spleen is located in the left upper quadrant of the abdominal cavity, just inferior to the diaphragm.

• It has a delicate structure and is situated in the left hypochondrium with its long axis paralleling the ninth to eleventh ribs.

Anatomy of the Spleen

• Location:

  • Posterolateral to the body and fundus of the stomach.

  • Posterolateral to the tail of the pancreas.

  • Posterior to the left colic flexure and inferior to the left kidney.

  • Posterior structures include the diaphragm, left lung, and ribs (8th to 11th).

• Structure:

  • Intraperitoneal, completely covered by peritoneum except for a small bare area at the hilum (medial surface).

  • The hilum allows passage for the splenic artery, splenic vein, and lymphatic vessels.

  • Composed of two main regions: Red Pulp and White Pulp.

Components of the Spleen

• Red Pulp:

  • Contains venous sinuses filled with blood and splenic cords (connective tissues with red and white blood cells).

• White Pulp:

  • Primarily consists of immune cells, specifically T cells and B cells.

Functions of the Spleen

• Part of the reticuloendothelial system, responsible for:

  • Phagocytosis of damaged/old cells, foreign materials, and pathogens.

  • Functions include:

    • Filtration of blood and debris.

    • Hematopoiesis (blood formation), particularly during fetal life.

    • Destruction of red blood cells and platelets.

    • Serving as a blood reservoir.

Size and Shape of the Spleen

• Size:

  • Can vary from very small to large.

  • Changes in size due to blood pressure, meals, exercise, and aging.

• Shape:

  • Generally ovoid with smooth borders, featuring a convex superior surface and a concave inferior surface.

  • Can also take wedge-shaped, tetrahedral, or triangular forms.

Surfaces of the Spleen

• Visceral Surface:

  • Concave surface related to:

    • Stomach

    • Kidney

    • Colon

    • Tail of the pancreas

  • Concave hilar surface allows for entry/exit of splenic vessels.

• Parietal Surface:

  • Convex surface related to the diaphragm.

Vascular Supply and Drainage

• Supply:

  • Blood supplied by the splenic artery, the largest branch of the celiac trunk.

  • Enters at the splenic hilum, above and in front of the splenic vein.

• Drainage:

  • The splenic vein is the main vein draining the spleen.

  • Runs posterior to the pancreas and joins the superior mesenteric vein to form the portal vein.

Normal Texture and Patterns

• The spleen appears homogeneous and moderately echogenic on imaging studies.

Congenital Anomalies

• Common conditions include:

  • Splenic agenesis: complete absence of splenic tissue, associated with congenital heart disease.

  • Accessory spleen: small nodule of splenic tissue separate from the main body, found in ~10% of the population.

  • Wandering spleen: rare birth defect, spleen moves within the abdominal cavity due to absent or underdeveloped ligaments.

Removal of the Spleen

• After partial removal, the spleen may regenerate.

• Total splenectomy results in the inability to regenerate, but other organs compensate for its functions.

Sonography of the Spleen

• Normal spleen is homogeneous and isoechoic to the liver, measuring:

  • Length: 8-13 cm

  • Width: 7 cm

  • Thickness: 3-4 cm

• Best visualized along the long axis with deep inspiration and the patient on their right side.

Applications of Sonography

• Diagnostic Uses:

  • Detects splenomegaly (enlargement of the spleen).

  • Assesses splenic masses, though primary masses are rare.

  • Evaluates splenic damage due to trauma (e.g., rupture, hemorrhage).

• Spleen-Liver Interface:

  • In normal conditions, the liver does not contact the spleen. As the left lobe of the liver may enlarge, it can extend into the left upper quadrant, potentially anterior to the spleen, especially during pregnancy.