Spleen location and anatomy: the blood filter under your left ribs

What it is

The spleen is the largest lymphoid organ, filtering blood and supporting immune responses.

Location

It lies intraperitoneally in the left upper quadrant, against the diaphragm and posterolateral to the stomach, under ribs 9 to 11.

Function

It removes old red blood cells, stores platelets, and mounts immune responses to blood-borne antigens.

Body system

Lymphatic · single, midline structure

FMA ID

FMA7196 (Foundational Model of Anatomy)

Key facts

• Red pulp filters blood; white pulp contains lymphoid tissue.
• Supplied by the splenic artery from the celiac trunk.

Clinical relevance

It can rupture after left lower rib trauma, causing life-threatening bleeding; splenectomy raises infection risk.

The spleen is a wedge-shaped organ lying mainly in the left upper quadrant of the abdomen, largely within the left hypochondrium, the region under the left ribs. It is protected by the left 9th to 11th ribs, and its outer (diaphragmatic) surface lies against the dome of the left hemidiaphragm. (Radiopaedia: Spleen.)

TeachMeAnatomy places the spleen under cover of the diaphragm and rib cage, which is why a normal spleen is not palpable. In front of it is the stomach; behind it are the diaphragm, the left lung and ribs 9 to 11; below it is the left colic flexure; and medial to it are the left kidney and the tail of the pancreas. (TeachMeAnatomy: The Spleen.)

Kenhub describes the spleen as lying behind the stomach and in front of the left hemidiaphragm, at the level of ribs 9 and 10, with the left kidney medial to it, the diaphragm above it and the left colic flexure below it. (Kenhub: Spleen.)

On the transpyloric plane, a horizontal plane at about the level of L1, anatomists traditionally place the hilum of the spleen, together with the hila of the kidneys and the splenic flexure of the colon, although real bodies vary. (Radiopaedia: Transpyloric plane.)

An adult spleen is around 2.5 cm thick, 7.5 cm broad and 12 cm long, with a volume of about 100 to 300 cm³. It has two poles (superior and inferior), three borders (superior, inferior and intermediate) and two surfaces (diaphragmatic and visceral). (Radiopaedia: Spleen.)

OpenStax describes the spleen as about 12 cm long, fragile, without a strong capsule, and dark red because it has so many blood vessels. (OpenStax Anatomy and Physiology 2e, 21.1: Anatomy of the Lymphatic and Immune Systems.)

Kenhub calls it a purple, fist-sized organ whose fibroelastic capsule allows it to enlarge considerably when needed. (Kenhub: Spleen.)

Its anterior and superior borders carry notches, while the posteromedial and inferior borders are smooth. When the spleen enlarges, its superior border moves downwards and medially, and these notches can be felt below the left rib margin, which helps doctors recognise an enlarged spleen. (TeachMeAnatomy: The Spleen.)

The diaphragmatic (outer) surface is smooth and convex. It lies against the diaphragm, and the 9th to 11th ribs leave impressions on it. The visceral (inner) surface faces the abdominal organs and has colic, gastric and renal impressions, with the splenic hilum in its central part. (Kenhub: Spleen.)

Radiopaedia lists the visceral relations precisely: the tail of the pancreas medially, the left kidney and left adrenal gland posteromedially, the fundus and greater curvature of the stomach anteromedially, and the splenic flexure of the colon inferiorly. (Radiopaedia: Spleen.)

The spleen is intraperitoneal: it is entirely covered by peritoneum except at the hilum. Two peritoneal folds attach it. The gastrosplenic ligament runs from the hilum to the greater curvature of the stomach, in front of the hilum. The splenorenal ligament runs from behind the hilum to the left kidney and contains the splenic vessels and the tail of the pancreas. The lesser sac lies between the two. (TeachMeAnatomy: The Spleen.)

The gastrosplenic ligament carries the short gastric and left gastroepiploic vessels. A third fold, the phrenicocolic ligament, comes from the colon and is also called the sustentaculum lienis (Latin for 'support of the spleen'). (Kenhub: Spleen.)

The splenic artery is a branch of the coeliac (celiac) trunk. It runs to the left along the upper border of the pancreas and then through the splenorenal ligament to the hilum. There it divides into about five branches that do not join each other, so the spleen is made of separate vascular segments. This is what makes a partial (subtotal) splenectomy possible. (TeachMeAnatomy: The Spleen.)

The splenic vein leaves the hilum and joins the superior mesenteric vein behind the pancreas to form the hepatic portal vein, so blood from the spleen passes through the liver. Lymph drains to the splenic nodes, then the superior pancreatic nodes and finally the coeliac nodes. Nerves come from the coeliac plexus. (Kenhub: Spleen.)

Sympathetic fibres from the coeliac plexus influence splenic blood flow. Whether the spleen also has a parasympathetic (vagal) supply is debated in the literature. (Radiopaedia: Spleen.)

The spleen is sometimes called the filter of the blood. Its red pulp mainly filters blood, while its white pulp is where T and B cell (adaptive immune) responses are mounted. Macrophages and dendritic cells in the spleen remove microbes and other material from the blood, and the spleen is the site of immune responses to blood-borne pathogens. (OpenStax Anatomy and Physiology 2e, 21.1: Anatomy of the Lymphatic and Immune Systems.)

In the red pulp, macrophages remove old or damaged red blood cells. The spleen normally holds about one third of the body's platelets, and contractile cells in its trabeculae can squeeze stored blood back into the circulation, for example during intense exercise or heavy bleeding. Before birth the spleen also makes blood cells until the bone marrow takes over. (Kenhub: Spleen.)

A healthy spleen does not extend below the left costal margin, so it cannot be felt (palpated). An enlarged spleen grows downwards and can reach as far as the pubic symphysis in some diseases, such as mantle cell lymphoma. When the spleen is enlarged, the amount of platelets trapped in it can rise to about 90%, which can lower the platelet count. (Kenhub: Spleen.)

On ultrasound, a spleen length of 12 cm is generally taken as the upper limit of normal, although lengths up to 14 cm can be normal in tall men. Massive splenomegaly is defined as more than 15 cm on clinical examination, or a spleen that reaches the umbilicus, extends into the pelvis or crosses the midline. Causes include blood disorders, infections, portal hypertension, storage diseases and tumours. (Radiopaedia: Splenomegaly.)

The spleen is the most frequently injured internal organ after blunt trauma and can account for up to 49% of abdominal organ injuries in blunt trauma. Symptoms can include left upper quadrant pain, left chest pain and left shoulder tip pain, with signs of low blood pressure or shock. (Radiopaedia: Splenic injury.)

A rupture is a break in the fibroelastic capsule, usually from blunt or penetrating trauma and often together with fractures of the left lower ribs. Because the spleen is so vascular, rupture causes heavy bleeding into the peritoneal cavity. (TeachMeAnatomy: The Spleen.)

Most splenic injuries in patients whose circulation is stable are treated without surgery, and splenic artery embolisation (blocking the bleeding vessel from inside) plays a major role in severe injuries. Splenectomy is considered when CT shows major active bleeding. Delayed rupture occurs in about 5% of patients managed without surgery. (Radiopaedia: Splenic injury.)

The spleen is not a vital organ, and people can live without it. After splenectomy the liver and bone marrow take over some of its work, but people without a spleen are more prone to certain bacterial infections. (TeachMeAnatomy: The Spleen.)

For this reason, people without a spleen need lifelong vaccinations and, when necessary, preventive antibiotics. (Kenhub: Spleen.)

A splenunculus (accessory spleen, splenule) is a small nodule of normal spleen tissue separate from the main organ. It is present from birth, because the spleen develops from several buds that sometimes fail to fuse. Splenunculi are seen in up to 16% of abdominal CT scans and up to 30% of autopsies, most often at the splenic hilum, and are usually a few centimetres across. (Radiopaedia: Splenunculus.)

Accessory spleens are harmless, but they matter after splenectomy for conditions such as immune thrombocytopenia: an overlooked splenunculus can grow and cause the disease to return, so surgeons look for them before the operation. (Radiopaedia: Splenunculus.)

The spleen forms from several splenic buds that fuse within the dorsal mesentery of the embryonic foregut. Other variants include a wandering spleen, polysplenia, asplenia, a retrorenal spleen and splenic clefts, which can look like a tear on a scan. (Radiopaedia: Spleen.)

The nearest named structures in the 3D model, measured from the centre of each part:

• Hepatovenous segment VII · digestive
• Hepatovenous segment VI · digestive
• Tenth rib · skeletal
• Splenic artery · cardiovascular
• Adrenal gland · endocrine
• Ninth rib · skeletal
• Inferior suprarenal artery · cardiovascular
• Splenic vein · cardiovascular
• Inferior phrenic artery · cardiovascular
• Gastro-epiploic artery · cardiovascular