Structure
The spleen is a soft, purple, fist-sized organ with a smooth convex diaphragmatic surface and a concave visceral surface marked by the organs around it.
It has two poles and two borders. The superior border is sharp and typically notched near its lower end, a feature used to recognise an enlarged spleen on palpation. The inferior border is rounded. The hilum, on the visceral surface, transmits the splenic vessels and nerves.
Inside, a fibrous capsule sends trabeculae into the pulp. Red pulp consists of venous sinuses and splenic cords where aged or damaged red cells are removed. White pulp is lymphoid tissue sheathing the arterioles, where antibody responses to blood-borne antigens begin.
Peritoneal attachments
The spleen is intraperitoneal and hangs from two ligaments derived from the dorsal mesogastrium.
- Gastrosplenic ligament: hilum to greater curvature of the stomach, carrying the short gastric and left gastro-omental vessels.
- Splenorenal (lienorenal) ligament: hilum to the front of the left kidney, carrying the splenic vessels and the tail of the pancreas.
The phrenicocolic ligament, from the left colic flexure to the diaphragm, supports the lower pole but does not attach to the spleen.
Relations
The diaphragmatic surface faces the diaphragm, pleura, lung and ribs 9 to 11, while the visceral surface touches the stomach, left kidney, left colic flexure and tail of pancreas.
| Surface or area | Relation |
|---|---|
| Diaphragmatic surface | Diaphragm, separating it from the costodiaphragmatic recess of the left pleura, the base of the left lung and ribs 9 to 11 |
| Gastric impression | Fundus and body of the stomach, anterior to the hilum |
| Renal impression | Upper lateral part of the left kidney, posterior to the hilum |
| Colic impression | Left colic (splenic) flexure, at the anterior pole |
| Pancreatic area | Tail of the pancreas, at the hilum |
A normal spleen does not project below the costal margin and is not palpable. It moves with respiration because it lies against the diaphragm.
Blood supply and innervation
The splenic artery, the largest branch of the coeliac trunk, supplies the spleen after a tortuous course along the upper border of the pancreas.
On the way the artery gives pancreatic branches to the body and tail of the pancreas, and near the hilum it gives the short gastric arteries to the fundus and the left gastro-omental artery to the greater curvature. At the hilum it divides into several branches that supply separate vascular segments. These are end arteries, so blockage causes wedge-shaped infarcts, and partial splenectomy along segment planes is possible.
The splenic vein emerges from the hilum, runs straight behind the body of the pancreas, usually receives the inferior mesenteric vein, and joins the superior mesenteric vein behind the pancreatic neck to form the portal vein. Lymph passes to hilar and pancreaticosplenic nodes, then to coeliac nodes. Sympathetic nerves from the coeliac plexus accompany the artery.
Clinical relevance
The spleen is a vascular, friable organ that bleeds heavily when injured and is essential for defence against encapsulated bacteria.
- Blunt trauma: the spleen is among the organs most often injured in blunt abdominal trauma, especially with fractures of the left 9th to 11th ribs. Blood irritating the diaphragm may cause left shoulder tip pain (Kehr's sign) via the phrenic nerve, C3 to C5.
- Splenomegaly: the spleen enlarges downwards and medially towards the right iliac fossa, along the line of the 10th rib. It is dull to percussion, moves with respiration, has a palpable notch, and the examining hand cannot get above it, which distinguishes it from an enlarged left kidney.
- Splenectomy: the tail of the pancreas at the hilum and the stomach wall at the short gastric vessels are at risk. Afterwards the patient is vulnerable to overwhelming infection by encapsulated organisms such as Streptococcus pneumoniae, Haemophilus influenzae type b and Neisseria meningitidis, and needs vaccination.
- Accessory spleens (splenunculi): small nodules of splenic tissue, most often near the hilum or in the gastrosplenic ligament, which must be removed when splenectomy is done for haematological disease.