Pancreas and spleen anatomy
Pancreas and Spleen: Relations, Blood Supply, Development and Clinical Anatomy
Pancreas and spleen for FCPS Part 1: relations of each part of the pancreas, ducts, blood supply, development and the spleen's position, ligaments and structure. Covers pancreatitis, annular pancreas, splenic trauma and post-splenectomy changes.
Pancreas: parts and relations
A retroperitoneal gland lying across L1–L2, from the duodenal C to the splenic hilum, behind the stomach and lesser sac.
| Part | In front | Behind |
|---|---|---|
| Head (in the duodenal C) | Transverse mesocolon, pylorus | IVC, right renal vein, common bile duct (groove or tunnel in the back of the head) |
| Uncinate process | SMV and SMA | Aorta (and IVC) |
| Neck (transpyloric plane) | Pylorus, gastroduodenal artery | SMV joining the splenic vein to form the portal vein |
| Body | Lesser sac, stomach; root of transverse mesocolon along its anterior border | Aorta, SMA origin, left crus, left kidney and adrenal, splenic vein |
| Tail | Stomach | In the splenorenal ligament, reaching the splenic hilum |
- The splenic artery runs tortuously along the upper border of the pancreas; the splenic vein lies behind the body.
- The lesser sac separates stomach from pancreas. To expose the body widely, the surgeon divides the gastrocolic ligament.
- Cancer of the head obstructs the CBD early: painless jaundice with a palpable gallbladder (Courvoisier's law). Body and tail cancers present late with back pain.
- Pancreatic or posterior duodenal rupture leaks fluid into the retroperitoneum and lesser sac, not the greater sac.
Ducts and the ampulla
- Main duct (Wirsung) joins the CBD in the hepatopancreatic ampulla (of Vater), opening at the major duodenal papilla in D2, guarded by the sphincter of Oddi.
- Accessory duct (Santorini) drains the upper head through the minor papilla about 2 cm higher.
- Gallstone pancreatitis: a small stone impacts at the ampulla, obstructing the common channel; a mildly raised bilirubin or ALT supports a biliary cause even if no duct stone is seen.
- Pancreas divisum: dorsal and ventral ducts fail to fuse; most secretion leaves through the minor papilla.
Development
- Dorsal bud forms the upper head, neck, body and tail; the ventral bud (with the bile duct) rotates behind the duodenum to form the lower head and uncinate process. The main duct = ventral duct plus distal dorsal duct.
- Annular pancreas: abnormal ventral bud (a bifid bud migrating both ways) encircles D2. Neonatal vomiting (bilious if below the papilla) and a double bubble, like duodenal atresia; associated with Down syndrome.
Blood supply: a coeliac–SMA bridge
- Head: superior pancreaticoduodenal arteries (from gastroduodenal, coeliac) and inferior pancreaticoduodenal (from SMA) form anterior and posterior arcades.
- Body and tail: splenic artery branches, including the arteria pancreatica magna and dorsal pancreatic artery.
- These arcades link the coeliac and SMA territories. With a coeliac trunk stenosis, the liver is fed backwards from the SMA through the pancreaticoduodenal arcades and the gastroduodenal artery. Test-clamping the GDA in a Whipple operation then abolishes the common hepatic pulse; dividing it would starve the liver.
- Veins drain to the splenic vein, SMV and portal vein. Splenic vein thrombosis (pancreatitis) causes left-sided (sinistral) portal hypertension and isolated gastric fundal varices.
Exocrine and endocrine function
| Cell | Product | Stimulus or note |
|---|---|---|
| Acinar | Enzymes (trypsinogen, lipase, amylase) | CCK, vagus |
| Duct | Bicarbonate-rich fluid | Secretin |
| α (alpha) | Glucagon (the hyperglycaemic hormone) | Peripheral islet |
| β (beta) | Insulin | Most numerous, central |
| δ (delta) | Somatostatin | Inhibits both |
| PP | Pancreatic polypeptide | Mainly head (ventral bud) |
- Islets are densest in the tail.
- Loss of exocrine secretion: fat maldigestion (steatorrhoea), no micelle and chylomicron formation, deficiency of fat-soluble vitamins A, D, E, K; B12 absorption also falls because proteases free B12 from R-binder.
- Acute pancreatitis: enzymatic fat necrosis with calcium soaps; lipase is the more specific test; Grey Turner sign (flank bruising) and Cullen sign (periumbilical).
- Glucagonoma (usually body or tail): necrolytic migratory erythema in groins and buttocks, diabetes, weight loss, glossitis, anaemia, venous thrombosis. Somatostatinoma gives diabetes, gallstones and steatorrhoea instead.
Spleen: position and ligaments
- Left hypochondrium, behind the stomach, along ribs 9–11, long axis along the 10th rib; posterior border notched; not palpable until enlarged about three times, then grows towards the right iliac fossa.
- Relations: stomach (front), left kidney (back), splenic flexure (below), diaphragm (outside), tail of pancreas (hilum).
| Ligament | Contents or role |
|---|---|
| Gastrosplenic | Short gastric and left gastroepiploic vessels |
| Splenorenal | Splenic vessels, tail of pancreas |
| Phrenicocolic | Supports the lower pole; resists downward displacement |
- The costodiaphragmatic recess of pleura extends to the 10th rib in the midaxillary line. A needle in the left 10th intercostal space there passes through pleura (pneumothorax, effusion) before reaching the spleen; the lung edge is higher.
Spleen: structure and function
| Feature | Spleen | Lymph node |
|---|---|---|
| Lymphatics | No afferent lymphatics; filters blood | Afferent and efferent lymphatics; filters lymph |
| Compartments | White pulp (PALS T cells, follicles B cells), red pulp (cords and sinusoids) | Cortex, paracortex, medulla |
- Red pulp cords and sinusoids remove old and abnormal red cells, which must squeeze through slits in the sinusoid walls. Spherocytes are trapped here, so hereditary spherocytosis improves after splenectomy.
- White pulp mounts antibody responses to blood-borne encapsulated bacteria.
- Hypersplenism: an enlarged spleen (e.g. portal hypertension) pools up to a large fraction of the platelets; thrombocytopenia with normal marrow and normal platelet lifespan is due to pooling, not destruction.
Splenic trauma, aneurysm and splenectomy
- Commonest solid organ injured in blunt trauma, often with left lower rib fractures. Kehr's sign: left shoulder-tip pain from blood irritating the diaphragm, referred through the phrenic nerve (C3–C5).
- Splenic artery aneurysm: the commonest visceral aneurysm; ruptures particularly in late pregnancy; rim calcification near the hilum. Treated even when small in women who may become pregnant.
- After splenectomy: Howell–Jolly bodies, target cells, thrombocytosis; risk of overwhelming post-splenectomy infection (pneumococcus, *H. influenzae* type b, meningococcus); vaccinate (2 weeks before elective surgery) and give penicillin prophylaxis.
- Accessory spleens (10–20%, often at the hilum) can cause relapse of ITP.
- At risk in splenectomy: tail of pancreas (fistula), greater curvature of the stomach, splenic flexure.
Remember Portal vein behind the neck, CBD behind the head, SMV and SMA in front of the uncinate, splenic artery along the top.
Exam trap The uncinate process lies behind the SMV and SMA but in front of the aorta.
Exam trap Low platelets in hypersplenism are from pooling, not shortened survival.
How FCPS asks about this
- Posterior relation of the head of the pancreas: IVC (and the CBD in its groove); behind the neck: portal vein.
- Artery along the upper border of the pancreas: splenic artery; pancreatica magna is its branch.
- Annular pancreas: abnormal ventral bud encircling D2; double bubble.
- Splenic vessels ligated in splenectomy: in the splenorenal ligament with the pancreatic tail.
- Spleen versus lymph node: spleen has no afferent lymphatics; red pulp culls old red cells.
- Blood film after splenectomy: Howell–Jolly bodies; vaccinate against encapsulated organisms.
- Needle in the left 10th space midaxillary line: traverses the costodiaphragmatic recess, causing pneumothorax.
Test yourself on this topic
5 of the 40 questions in our bank on this topic. Choose an answer to see why every option is right or wrong.
A 25-year-old woman is booked for elective splenectomy for hereditary spherocytosis. Which of the following is the best time to give pneumococcal, Hib and meningococcal vaccines?
Answer: At least 2 weeks before surgery
The spleen filters blood-borne bacteria and is a major site for making antibody against polysaccharide capsules, so asplenic patients are at risk of overwhelming infection with encapsulated organisms. Vaccines produce the best antibody response while the spleen is still present, so for elective splenectomy they are given at least 2 weeks before surgery. After emergency splenectomy they are given about 2 weeks after operation, when the immune response has recovered from surgery. Lifelong advice and antibiotic prophylaxis are also given.
Splenectomy vaccines
- Elective: at least 2 weeks before
- Emergency: about 2 weeks after
- Pneumococcus, Hib, meningococcus, influenza
- Plus antibiotic prophylaxis and a card
Remember Vaccinate while the spleen can still respond.
Exam trap The timing differs for elective and emergency splenectomy.
Why the other options are wrong
- On the day of surgery Too late for a good response before the spleen is lost.
- Two weeks after surgery The timing for emergency, not elective, splenectomy.
- Six months after surgery Leaves her unprotected for months.
- Only if she develops infection Prevention, not treatment, is the aim.
After splenectomy for trauma, a patient is at greatest risk of overwhelming infection with which group of organisms?
Answer: Encapsulated bacteria
The spleen filters blood, removes old red cells and inclusions, makes IgM antibodies against polysaccharide capsules and is a major site of phagocytosis of opsonised organisms. Without it, encapsulated bacteria (Streptococcus pneumoniae, Haemophilus influenzae type b, Neisseria meningitidis) can cause overwhelming post-splenectomy infection. Patients need pneumococcal, Hib, meningococcal and yearly influenza vaccines (ideally two weeks before elective splenectomy) and often prophylactic penicillin. The blood film shows Howell-Jolly bodies and target cells.
After splenectomy
- Risk: encapsulated bacteria (pneumococcus, Hib, meningococcus)
- Vaccinate 2 weeks before elective surgery
- Film: Howell-Jolly bodies, target cells
Remember No spleen, capsules win.
Why the other options are wrong
- Anaerobic bacteria Not the main risk.
- Fungi such as Candida Not specifically linked.
- Herpes viruses Not specifically linked.
- Intestinal helminths Not linked.
Before laparoscopic splenectomy for ITP, the surgeon plans to search for accessory spleens, which would otherwise cause relapse. Which of the following is their commonest site?
Answer: Splenic hilum
Accessory spleens (splenunculi) arise when separate clusters of mesenchyme in the dorsal mesogastrium fail to fuse with the main spleen. They are found in about one in ten people, most often at the splenic hilum, followed by the gastrosplenic and splenorenal ligaments, the tail of the pancreas and the greater omentum. In ITP, a missed splenunculus continues to destroy platelets and causes relapse, so the hilum and ligaments are searched carefully at operation.
Accessory spleen
- From dorsal mesogastrium
- Commonest at splenic hilum
- Then gastrosplenic, splenorenal ligaments
- Missed one: ITP relapse
Remember Look at the hilum first.
Exam trap After splenectomy, absence of Howell-Jolly bodies suggests residual splenic tissue.
Why the other options are wrong
- Greater omentum A recognised but less common site.
- Pelvis near the ovary Rare; usually with splenogonadal fusion.
- Mesentery of jejunum Rare site.
- Right subphrenic space On the wrong side; spleen develops in the left dorsal mesogastrium.
A 50-year-old woman with small gallstones has sudden epigastric pain radiating to the back, amylase 1,800 U/L and a mildly raised bilirubin. Where does the stone most likely cause the pancreatitis?
Answer: Stone impacted at the ampulla of Vater
The common bile duct runs behind and then through the head of the pancreas, joining the main pancreatic duct to form a short common channel at the ampulla of Vater. A small stone passing down the duct can impact at the ampulla, obstructing both bile and pancreatic outflow. The rise in pancreatic duct pressure, with or without bile reflux, triggers premature enzyme activation and acute pancreatitis. Small stones are more dangerous than large ones because they can migrate into the duct.
Gallstone pancreatitis
- Small stone impacts at ampulla
- Blocks common channel
- Raised pancreatic duct pressure
- Small stones are riskier
Remember The stone at the shared exit blocks both ducts.
Exam trap A mildly raised bilirubin or ALT supports a biliary cause even when ultrasound shows no duct stone.
Why the other options are wrong
- Stone impacted in the cystic duct Causes cholecystitis, not pancreatitis.
- Stone in the gallbladder neck Causes biliary colic or cholecystitis.
- Stone in the common hepatic duct Above the pancreatic duct junction; causes jaundice only.
- Stone in the dorsal pancreatic duct Gallstones do not enter it.
Which peritoneal fold supports the lower pole of the spleen from below and helps limit its downward movement?
Answer: Phrenicocolic ligament
The phrenicocolic ligament runs from the splenic flexure of the colon to the diaphragm and forms a shelf under the lower pole of the spleen. It limits downward movement and also guides an enlarging spleen forwards and towards the right iliac fossa. The gastrosplenic ligament carries the short gastric and left gastroepiploic vessels; the splenorenal ligament carries the splenic vessels and tail of the pancreas.
Splenic ligaments
- Phrenicocolic: shelf under spleen
- Gastrosplenic: short gastrics
- Splenorenal: splenic vessels, pancreatic tail
- Spleen enlarges towards right iliac fossa
Remember The colon's shelf holds the spleen up.
Exam trap Tail of pancreas lies in the splenorenal ligament and can be injured at splenectomy.
Why the other options are wrong
- Gastrosplenic ligament Contains short gastric vessels.
- Splenorenal ligament Contains splenic vessels and pancreatic tail.
- Falciform ligament Attaches the liver to the anterior wall.
- Hepatoduodenal ligament Contains the portal triad.
Where this sits in the CPSP syllabus
- Paper 1: Abdomen, Pancreas and spleen
- Surgery & Allied, Paper 2: Abdomen, Pancreas and spleen
Read next
Drug dose pages
Doses, cautions and practical tips for drugs in this chapter.