The Spleen: The Organ You Can Live Without — At a Price
No organ in the body is dismissed so casually and misunderstood so completely. The spleen is not essential in the way the liver or a kidney is essential — surgeons remove it and patients walk out of hospital a week later — and yet it is the largest lymphoid organ you own, a filter through which a quarter of a litre of blood passes every minute, and the single most commonly injured organ in blunt abdominal trauma. It is the size of a clenched fist, the colour of a dark plum, and so soft that a surgeon's finger can tear it. A teenager who takes a bicycle handlebar to the left flank can be dead within the hour from an organ most people could not point to. Learn where it hides, what holds it, what feeds it, and what it does — and every one of those facts turns out to be clinical.
A seventeen-year-old is brought in after coming off his bicycle. He was not going fast, he did not hit his head, and the handlebar caught him just once, under the left ribs. In the ambulance he was talking; in the resuscitation bay he is pale, his pulse is climbing, and he keeps asking the nurse to fix his left shoulder — a shoulder that was never touched, that is not tender, that moves perfectly. The registrar does not examine the shoulder. She puts an ultrasound probe under the left costal margin, sees free fluid where none should be, and calls the theatre. Somewhere behind the ninth, tenth and eleventh ribs, an organ softer than liver and richer in blood than a kidney has split along its capsule, and it is emptying his circulation into his belly. The pain in his shoulder is blood lapping against the undersurface of the diaphragm, irritating a nerve that entered the spinal cord at C4. Nothing about that shoulder was ever wrong. It was the spleen, calling from a long way off.
The rule of odds: where the spleen hides
1, 3, 5, 7, 9, 11 — six odd numbers that hold the entire surface anatomy of the organ. The spleen measures roughly ONE by THREE by FIVE inches, weighs about SEVEN ounces (some 150 grams in the adult), and lies deep to ribs NINE, TEN and ELEVEN on the left. That single mnemonic tells you almost everything a clinician needs. It occupies the LEFT HYPOCHONDRIUM, tucked high under the dome of the diaphragm, with its long axis lying along the line of the TENTH RIB — which is why it is directed downwards, forwards and laterally rather than straight down, and why a rib fracture on the left is never an innocent finding. Between the spleen and the ribs sit the diaphragm and the costodiaphragmatic recess of the left pleural cavity, so the organ is separated from the outside world by muscle, pleura and bone, and is entirely hidden behind the costal margin in health. It is INTRAPERITONEAL: developed within the dorsal mesogastrium, it is wrapped in visceral peritoneum over its whole surface except at the hilum, a relationship set out in the peritoneum. Its DIAPHRAGMATIC surface is smooth and convex, moulded to the dome above it. Its VISCERAL surface is irregular and carries the impressions of everything that presses on it: a GASTRIC impression for the fundus of the stomach, a RENAL impression for the left kidney, a COLIC impression for the splenic flexure, and a small PANCREATIC impression where the tail of the pancreas reaches the hilum. And its superior border is NOTCHED — two or three shallow clefts, remnants of the fetal lobules from which the organ fused — which is the single feature that will let you recognise it under your fingers when it enlarges.
Two ligaments, and why one of them costs the pancreas
The spleen is suspended, not fixed — and each suspension carries vessels. Because it grew inside the dorsal mesogastrium, the spleen ends up slung between two double folds of peritoneum, described alongside its neighbours in the mesenteries, omenta and peritoneal ligaments. The GASTROSPLENIC LIGAMENT runs forwards from the hilum to the greater curvature of the stomach and carries the SHORT GASTRIC vessels and the LEFT GASTRO-OMENTAL vessels — which is why the surgeon dividing this ligament in a splenectomy must take care not to tear the wall of the stomach itself, since the short gastrics are very short indeed. The SPLENORENAL (lienorenal) LIGAMENT runs backwards from the hilum to the anterior surface of the left kidney and carries the SPLENIC ARTERY, the SPLENIC VEIN — and the TAIL OF THE PANCREAS, which reaches into the ligament and touches the hilum in about a third of people. That last fact is the reason a pancreatic fistula is a recognised complication of splenectomy: the two organs share a ligament, and a clamp placed blindly across the hilum can take a bite out of the pancreas as well. A third fold, the PHRENICOCOLIC LIGAMENT, runs from the diaphragm to the splenic flexure of the colon and forms a shelf on which the lower pole of the spleen rests — the organ's floor rather than its ceiling. At the HILUM, on the visceral surface between the gastric and renal impressions, the vessels enter and leave; and because the splenic artery divides into terminal branches that do not anastomose with one another, the spleen is a SEGMENTAL organ with relatively avascular planes between segments — which is what makes partial splenectomy and splenic conservation surgery possible at all.
Think of the spleen as the customs post on a river, built where the current is forced to slow down. Every red cell in the body passes through it every few days, and the checkpoint has two departments working side by side. The first is QUALITY CONTROL: the cell must squeeze through a slit barely three micrometres wide to re-enter the bloodstream, and a stiff, old or damaged cell simply cannot make the turnstile — it is pulled aside and destroyed. Officers also reach inside the cells that do pass, plucking out inclusions (a leftover fragment of nucleus, a clump of denatured haemoglobin) and letting the repaired cell go on its way. The second department is INTELLIGENCE: an enormous archive of lymphocytes sits along the arterial channels reading every organism the blood carries, and it is uniquely good at recognising bacteria wrapped in a slippery polysaccharide coat that the rest of the immune system struggles to grip. Close the customs post and the river still flows — but nobody inspects the cargo any more, and nothing catches the encapsulated smugglers.
The most tortuous artery in the body
The SPLENIC ARTERY is the LARGEST branch of the coeliac trunk, and it is instantly recognisable at operation and on a CT scan because it is famously TORTUOUS — it does not run to the spleen, it meanders there, snaking along the UPPER BORDER OF THE BODY OF THE PANCREAS in a series of loops that become more exaggerated with age. The tortuosity is not decoration: it is slack in the line, allowing the artery to accommodate the movement of the diaphragm and the changing volume of an organ that can swell and shrink. Along the way it gives PANCREATIC branches (including the dorsal pancreatic and the arteria pancreatica magna), then, as it approaches the hilum within the splenorenal ligament, it gives the SHORT GASTRIC arteries to the fundus of the stomach and the LEFT GASTRO-OMENTAL artery to the greater curvature — the reason the fundus survives when the spleen is removed is that it has other sources, and the reason a splenic artery aneurysm (the commonest visceral artery aneurysm, and dangerous in pregnancy) sits where it does is this long, redundant, high-flow course. The artery finally divides into five or so terminal branches that enter the hilum and supply the segments. Venous drainage is the mirror image with one crucial difference: the SPLENIC VEIN, formed by tributaries leaving the hilum, runs a STRAIGHT course BEHIND the body of the pancreas — not along its upper border — receiving the inferior mesenteric vein on the way, and joins the SUPERIOR MESENTERIC VEIN behind the neck of the pancreas to form the PORTAL VEIN. The spleen therefore drains into the portal system, not the systemic one, and that single fact explains why a liver that will not let blood through backs pressure up into the spleen; the consequences are traced in the portal system and the IVC. It also explains a curious local syndrome: inflammation in the pancreas lies directly on the splenic vein, and thrombosis of that vein produces LEFT-SIDED (sinistral) portal hypertension with isolated gastric varices and a big spleen, in a patient whose liver is entirely normal.
Three organs are welded together at the left upper quadrant by accident of development, and a surgeon cannot touch one without thinking of the other two. The TAIL OF THE PANCREAS lies in the splenorenal ligament, so it is injured in splenectomy. The SPLENIC VEIN lies on the back of the pancreas, so pancreatitis thromboses it. The FUNDUS OF THE STOMACH is tethered to the splenic hilum by the very short gastric vessels, so a hard pull on the spleen tears the stomach. Everything in that corner is bound to everything else by a mesentery that began life as a single sheet — the dorsal mesogastrium — and the anatomy of the duodenum and pancreas is unintelligible without it.
White pulp, red pulp: two organs in one capsule
Cut a fresh spleen and the naked eye already sees the division: grey specks scattered through a dark red matrix. The organ is wrapped in a thin FIBROELASTIC CAPSULE from which TRABECULAE run inwards, carrying the vessels and dividing the substance into a spongy framework of reticular tissue. In some mammals that capsule is packed with smooth muscle and the spleen can contract like a bladder to dump stored blood into the circulation; in humans the muscle is scanty, so the reservoir function is modest — the human spleen stores about a third of the body's PLATELETS and a modest volume of red cells rather than acting as a true blood tank. WHITE PULP is lymphoid tissue arranged around the arteries: as each arteriole leaves a trabecula it acquires a sleeve of T lymphocytes, the PERIARTERIOLAR LYMPHOID SHEATH (PALS), and at intervals this sheath swells into a lymphoid FOLLICLE of B cells with a germinal centre. The white pulp is the body's filter for BLOOD-BORNE antigen in exactly the way a lymph node is the filter for tissue fluid — a division of labour laid out in lymphatics and the body cavities. It is where opsonising IgM antibody is generated, and where the marginal zone B cells live that respond to the polysaccharide capsules of pneumococcus, meningococcus and Haemophilus. RED PULP is everything else: broad venous SINUSOIDS with slit-like gaps between their lining cells, separated by the CORDS OF BILLROTH, which are packed with macrophages. Blood is discharged from the arterioles into these cords, and to get home a red cell must deform itself through a three-micrometre slit into a sinusoid. This is the mechanism of CULLING — old, spherocytic or rigid cells fail the test and are eaten — and of PITTING, in which a macrophage removes an inclusion without destroying the cell: HOWELL–JOLLY BODIES (nuclear remnants), Heinz bodies and Pappenheimer bodies all disappear from the blood film because the spleen removes them, and all reappear after it is taken out.
Put the two pulps together and the functions of the spleen fall into four groups. FILTRATION: the removal of senescent red cells (which is why the spleen is a major site of extravascular haemolysis) and of circulating particles and inclusions. IMMUNITY: antigen presentation, antibody production, and the clearance of opsonised bacteria — above all ENCAPSULATED organisms, whose polysaccharide coats resist ordinary phagocytosis and are dealt with almost exclusively here. HAEMATOPOIESIS: the spleen makes blood cells in the FETUS, from roughly the third to the fifth month of intrauterine life, and can resume that role in adult disease as EXTRAMEDULLARY haematopoiesis when the marrow is crowded out by fibrosis or malignancy — one of the reasons a spleen may reach the pelvis in myelofibrosis. RESERVOIR: the storage of platelets, and in some species a substantial red cell volume that can be autotransfused on demand. Structure explains every one of these: white pulp does the immunology, red pulp does the filtering, and a soft reticular framework rich in blood does the rest.
Why a big spleen always grows the same way
A normal spleen is never palpable. By the time you can feel it, it has roughly doubled. In health the spleen hides completely behind ribs 9 to 11, and it must enlarge to about TWICE its normal size — some say three times — before its lower pole appears below the left costal margin. When it does enlarge, it cannot go upwards, because the diaphragm and the ribs are in the way; it cannot easily go backwards, because the left kidney and the posterior abdominal wall block it; and the phrenicocolic ligament holds its lower pole. So it grows along the ONLY available line, downwards and medially, towards the UMBILICUS and then the RIGHT ILIAC FOSSA. That single geometric fact generates the four classic bedside features that separate a spleen from a left kidney, and they are worth memorising as a set. First, the enlarging spleen MOVES WITH RESPIRATION, descending on inspiration, because it hangs from the diaphragm. Second, YOU CANNOT GET ABOVE IT — the examining fingers cannot be insinuated between the mass and the left costal margin, because the mass is continuous with something under the ribs. Third, it is DULL TO PERCUSSION, since it lies in front of the gut and pushes the gas-filled colon aside, whereas a renal mass has resonant colon in front of it. Fourth, its medial edge carries a palpable NOTCH. Add a fifth negative: the spleen is not ballottable, because it is intraperitoneal, while a kidney is retroperitoneal and can be bounced between two hands. Every one of those signs is anatomy, not memorisation.
The causes of splenomegaly sort themselves into the same functional headings. CONGESTION from portal hypertension — cirrhosis, portal or splenic vein thrombosis, cardiac failure — is the commonest cause in the West, and it comes with the other portosystemic signs, especially the oesophageal varices that share the same raised pressure. INFECTION: malaria and visceral leishmaniasis are the commonest causes worldwide and produce the biggest spleens; infectious mononucleosis produces a moderately enlarged and dangerously fragile one, which is why contact sport is forbidden for weeks after glandular fever. HAEMATOLOGICAL disease: chronic myeloid leukaemia, myelofibrosis, lymphoma, and the chronic haemolytic anaemias in which the spleen is working overtime. INFILTRATION: amyloid and the storage disorders such as Gaucher's disease. And when an enlarged spleen begins to destroy cells indiscriminately — pancytopenia in the blood, a hypercellular marrow trying to compensate, and correction of the counts when the organ is removed — the state is called HYPERSPLENISM. Note that hypersplenism is a functional diagnosis, not a size: a spleen can be huge and behave itself, or moderately enlarged and be eating the circulation.
THE DELAYED BLEED: a cyclist is discharged after a minor fall with a normal scan, and collapses at home on the third day. His capsule held at first, and blood accumulated slowly beneath it as a SUBCAPSULAR HAEMATOMA until the capsule finally gave way — the classic two-stage or delayed rupture, and the reason a significant left-sided injury earns observation rather than reassurance. THE FORGOTTEN VACCINE: a woman had her spleen removed at nineteen after a car crash. Twenty-two years later she develops a fever and a headache one afternoon and is in septic shock by midnight with purpura over her limbs — OVERWHELMING POST-SPLENECTOMY INFECTION with pneumococcus, a fulminant illness with a mortality near fifty per cent, in a patient who felt entirely well that morning and had never been told the risk was lifelong. THE SPLEEN THAT CAME BACK: a young man has a splenectomy for immune thrombocytopenia and his platelet count recovers beautifully — then falls again two years later. His blood film has no Howell–Jolly bodies, which it should have; a scan finds an ACCESSORY SPLEEN, a splenunculus near the hilum, present in ten to thirty per cent of people, quietly doing the job the surgeon thought he had abolished.
Taking it out, and living without it
Splenectomy is done for uncontrolled traumatic bleeding, for haematological disease (hereditary spherocytosis, refractory immune thrombocytopenia, some lymphomas), for symptomatic massive splenomegaly, and occasionally as part of an operation on the stomach or pancreas. Modern practice tries hard to avoid it in trauma — the segmental blood supply allows partial resection, and angiographic embolisation can save many spleens — precisely because the price of removal is permanent. The immediate hazards are the pancreatic tail and the greater curvature of the stomach; the early ones are a reactive THROMBOCYTOSIS and left lower lobe atelectasis; the lifelong one is OVERWHELMING POST-SPLENECTOMY INFECTION. Without white pulp there is nothing left that reliably clears encapsulated bacteria from the blood, so Streptococcus pneumoniae, Haemophilus influenzae type b and Neisseria meningitidis can go from colonisation to fulminant septicaemia in hours; the same defect explains severe malaria, babesiosis, and the catastrophic Capnocytophaga infection that can follow a dog bite. The risk is greatest in the first two years and in children, but it never returns to zero. Hence the standard package: vaccination against pneumococcus, Hib and meningococcus, ideally given at least two weeks BEFORE an elective splenectomy (when the immune response is better) with boosters thereafter, annual influenza vaccine, long-term prophylactic penicillin, a card or bracelet the patient carries, standby antibiotics for fever, and advice before travel to malarious areas. Anatomically the patient loses very little; immunologically they have lost a checkpoint that cannot be rebuilt.
The blood film is the spleen's signature. In a healthy person, red cells are clean because the red pulp pits every inclusion out of them as they squeeze through the sinusoidal slits. So the appearance of HOWELL–JOLLY BODIES — small round remnants of nuclear DNA inside circulating red cells — is a laboratory announcement that the spleen is absent or not working. It confirms a successful splenectomy; it reveals a functionally asplenic patient in sickle cell disease, coeliac disease or after radiotherapy; and its ABSENCE after splenectomy should make you hunt for an accessory spleen. A haematologist can tell you whether an organ has been removed from a patient's abdomen by looking at a drop of their blood under a microscope.
- The spleen is the largest lymphoid organ: about 1 × 3 × 5 inches, 7 ounces, lying deep to ribs 9–11 in the left hypochondrium with its long axis along the TENTH RIB — the mnemonic 1, 3, 5, 7, 9, 11.
- It is INTRAPERITONEAL, covered everywhere except at the hilum; the smooth diaphragmatic surface faces the dome, and the visceral surface bears gastric, renal, colic and pancreatic impressions. The superior border is NOTCHED.
- GASTROSPLENIC ligament carries the short gastric and left gastro-omental vessels; SPLENORENAL ligament carries the splenic artery and vein AND the tail of the pancreas — hence pancreatic injury in splenectomy. The phrenicocolic ligament supports the lower pole.
- The SPLENIC ARTERY is the largest branch of the coeliac trunk, tortuous along the upper border of the pancreas, giving pancreatic, short gastric and left gastro-omental branches before dividing at the hilum into non-anastomosing segmental branches.
- The SPLENIC VEIN runs straight BEHIND the pancreas, takes the inferior mesenteric vein, and joins the superior mesenteric vein behind the neck of the pancreas to form the PORTAL VEIN — so the spleen drains into the portal system.
- Segmental blood supply with relatively avascular planes makes PARTIAL splenectomy and splenic conservation possible.
- WHITE PULP = periarteriolar lymphoid sheaths (T cells) plus follicles with germinal centres (B cells): immune surveillance of BLOOD-borne antigen, IgM production, and clearance of ENCAPSULATED organisms.
- RED PULP = venous sinusoids with 3-micrometre slits plus the cords of Billroth: CULLING of old and rigid red cells and PITTING of inclusions (Howell–Jolly, Heinz, Pappenheimer bodies); it also stores about a third of the body's platelets.
- Functions: filtration, immunity, haematopoiesis (fetal months 3–5, and extramedullary in adult marrow disease), and reservoir.
- The four rules of a big spleen: it enlarges DOWNWARDS AND MEDIALLY towards the right iliac fossa, MOVES with respiration, you CANNOT GET ABOVE IT, it is DULL to percussion, and it has a NOTCH — and unlike a kidney it is not ballottable.
- It must roughly DOUBLE in size before it becomes palpable, so any palpable spleen is abnormal. Causes: portal hypertension, malaria and leishmaniasis, haematological disease, infection and infiltration.
- After splenectomy: lifelong risk of OPSI from encapsulated organisms — vaccinate (pneumococcus, Hib, meningococcus) at least two weeks before elective surgery, give prophylactic penicillin, and warn the patient forever.
- Thinking a spleen you can just feel is only slightly enlarged. It is at least twice normal size — the normal spleen is entirely hidden behind ribs 9 to 11 and is NEVER palpable in health.
- Placing the splenic vein along the UPPER border of the pancreas because that is where the artery runs. The artery is tortuous along the upper border; the vein runs straight BEHIND the gland — which is why pancreatitis thromboses the vein, not the artery.
- Assuming a splenectomised patient is immunologically normal once the wound heals. The loss of white pulp is permanent, the risk of overwhelming infection by encapsulated bacteria is lifelong, and the presenting symptom may be nothing more than a fever.
During an elective splenectomy the surgeon divides the ligament running from the splenic hilum to the anterior surface of the left kidney. Which structure is at greatest risk of injury within this ligament, and what complication follows?
- Remember the rule of odds — 1 × 3 × 5 inches, 7 ounces, behind ribs 9–11 — with the long axis along the tenth rib in the left hypochondrium; the spleen is intraperitoneal, notched on its superior border, and hidden behind the costal margin in health.
- Two ligaments hold it: gastrosplenic (short gastric and left gastro-omental vessels) and splenorenal (splenic vessels plus the TAIL OF THE PANCREAS); the tortuous splenic artery is the largest branch of the coeliac trunk along the upper border of the pancreas, while the splenic vein runs behind the gland to join the SMV and form the portal vein.
- White pulp (PALS and follicles) handles immunity against blood-borne and encapsulated organisms; red pulp (sinusoids and cords of Billroth) culls old red cells and pits out inclusions such as Howell–Jolly bodies, and stores a third of the platelets.
- Clinically: it must double before it is palpable and then enlarges towards the right iliac fossa, moves with respiration, cannot be reached above, is dull and notched; rupture gives shock with Kehr's sign; and splenectomy carries a lifelong risk of overwhelming infection by encapsulated bacteria.
- Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students — Abdomen: the spleen, its peritoneal ligaments and the splenic vessels.
- Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy — The spleen: surface anatomy, relations, splenectomy and splenic rupture.
- Netter FH. Atlas of Human Anatomy — Spleen in situ; coeliac trunk and splenic artery; portal venous system.
- Last RJ. Last's Anatomy: Regional and Applied — The spleen and the dorsal mesogastrium.
- Snell RS. Clinical Anatomy by Regions — The spleen: splenomegaly, trauma and accessory spleens.
- TeachMeAnatomy — The Spleen; The Coeliac Trunk.
