Spleen

The spleen is an organ of the haematological system and has a role in immune response, storage of red blood cells and haematopoiesis.

Gross anatomy

The spleen is a wedge-shaped organ lying mainly in the left upper quadrant (left hypochondrium and partly in the epigastrium) and is protected by the left 9^th to 11^th ribs. It is soft, highly vascular and dark purple in colour. Embryologically it forms within the ventral mesentery.

Size and weight vary from person-to-person but on average is around 2.5 cm thick, 7.5 cm broad and 12.5 cm in length. For paediatric measurements, see the article spleen size (paediatric)

The spleen has two poles (superior and inferior), three borders and two surfaces (diaphragmatic and visceral). It is enclosed by a thin capsule, which is easily ruptured. 

The spleen is completely covered by peritoneum, except at the hilum, which forms a number of ligaments ^6,7:

• gastrosplenic ligament
  • attaches the spleen to the greater curvature of the stomach
  • contains short gastric and left gastroepiploic arteries
• splenorenal ligament
  • attaches the spleen to the left kidney
  • contains splenic artery and vein and the pancreatic tail

Relations

• diaphragmatic surface (superoposteriorly): dome of the left hemidiaphragm
• visceral surface (anteromedially)
  • pancreatic tail
  • left kidney and adrenal gland
  • stomach

Arterial supply

• splenic artery

Venous drainage

• splenic vein

Lymphatic drainage

• from splenic hilar lymph nodes to retropancreatic lymph nodes, then draining to coeliac lymph nodes

Innervation

• sympathetic supply via coeliac plexus
• parasympathetic supply via vagal trunks

Variant anatomy

• ~10% of patients are noted to have an accessory spleen (splenunculus), most commonly adjacent to the splenic hilum with a mean size of 10 mm ²
• wandering spleen
• polysplenia
• asplenia
• splenogonadal fusion
• retrorenal spleen

Radiographic appearance

Ultrasound

• best assessed in the supine, left lateral position with the left arm placed behind the head
• visualized best obliquely in the 9th or 10th intercostal spaces
• echogenicity usually higher when compared to the liver, but may be iso- or hypoechoic

CT

• splenic parenchyma should be assessed in portal venous phase as inhomogeneous splenic enhancement (zebra or psychedelic spleen) seen on arterial phase can mimic splenic laceration or contusion ⁵