Spleen

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

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 color.

Size and weight vary from person-to-person but on average is around 2.5 cm thick, 7.5 cm broad and 12 cm in length. Its volume is on average between 100 to 300 cm^{3 12}. For pediatric measurements, see the article spleen size (pediatric)

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

The diaphragmatic surface contains impressions from the 9^th to 11^th ribs. The visceral surface has three impressions. The gastric area for the stomach, colic area for the splenic flexure of the colon and renal area for the left kidney.

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, left 9^th to 11^th ribs

• visceral surface 

  • pancreatic tail - medial 

  • left kidney and adrenal gland - posteromedial 

  • stomach - anteromedial 

  • splenic flexure of the transverse colon - inferior

Arterial supply

• splenic artery

Venous drainage

• splenic vein

Lymphatic drainage

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

Innervation

• sympathetic: via the celiac plexus (influence blood flow) ⁹

• parasympathetic: possibly via the vagal trunks ⁹, however there is contention in the literature as to whether the spleen has vagal (or any parasympathetic) innervation ^13,14

Variant anatomy

• splenunculus

• wandering spleen

• polysplenia

• asplenia

• splenogonadal fusion

• retrorenal spleen

• bilobar spleen ¹¹

• splenic cleft: may mimic traumatic laceration

Radiographic appearance

Ultrasound

• best assessed in the supine, right lateral position with the left arm placed behind the head

• visualized best obliquely in the 9^th or 10^th intercostal spaces

• echogenicity usually higher when compared to the liver, but may be iso- or hypoechoic

CT

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

Development

Embryologically, the spleen forms from several splenic buds that fuse together within the dorsal mesentery of the foregut (dorsal mesogastrium) ¹⁰.

Related pathology

• splenic lesions and anomalies