Pancreas and Spleen

An elongated, retroperitoneal gland lying transversely across the posterior abdominal wall, at approximately the L1-L2 vertebral level (transpyloric plane, see Overview section), extending from the duodenal C-loop to the splenic hilum.

• Functions as both an exocrine gland (digestive enzymes, via the pancreatic duct system) and an endocrine gland (insulin, glucagon, etc., via the islets of Langerhans, secreted directly into the bloodstream).

Parts:

• Head: The widest part, nestled within the C-shaped curve of the duodenum (right side); lies anterior to the IVC and the right renal vessels.
• Uncinate process: A hook-like extension of the head, projecting posteriorly and to the left, passing posterior to the superior mesenteric vessels (SMA and SMV), this relationship is the key anatomical feature of the uncinate process, since the SMA/SMV pass anterior to it, sandwiching it against the aorta/IVC posteriorly.
• Neck: A short, narrow segment connecting the head to the body, lying directly anterior to the origin of the portal vein (formed here by the union of the SMV and splenic vein), a critical anatomical landmark, since the portal vein's formation occurs precisely posterior to the pancreatic neck.
• Body: The main, elongated portion, crossing the midline anterior to the aorta (at the level of the L1-L2 transpyloric plane), related posteriorly to the splenic vein (running along its posterior surface) and, more posteriorly still, the left kidney and left suprarenal gland.
• Tail: The narrow, tapering left end, extending toward (and often making contact with) the splenic hilum, lying within the splenorenal (lienorenal) ligament: the only part of the pancreas that is (variably) intraperitoneal, given its position within this peritoneal fold, in contrast to the rest of the gland which is secondarily retroperitoneal.

Pancreatic duct:

• Main pancreatic duct (of Wirsung): Runs the length of the gland from tail to head, joining the common bile duct to form the hepatopancreatic ampulla, opening at the major duodenal papilla.
• Accessory pancreatic duct (of Santorini): A smaller duct draining the anterosuperior part of the head, typically opening separately at the minor duodenal papilla (proximal to the major papilla); in most individuals communicates with the main duct, but in a minority remains the dominant/sole drainage pathway for part of the head (a variant relevant to recurrent pancreatitis in some congenital ductal anomalies, e.g., pancreas divisum).

Important relations:

• Duodenum: Intimately related throughout, the head sits within the duodenal C-loop, sharing blood supply (pancreaticoduodenal arcades) and embryological origin, meaning duodenal and pancreatic head resections are typically performed together (Whipple procedure).
• Portal vein formation: Occurs directly posterior to the pancreatic neck (SMV + splenic vein union), a key surgical landmark, since this relationship means pancreatic neck pathology or surgery carries direct risk to the portal vein's formation.
• SMA and SMV: Pass anterior to the uncinate process (and posterior to the pancreatic neck, at the neck/body junction), the SMA/SMV are therefore sandwiched between the pancreatic neck (anteriorly) and the uncinate process (which wraps posteriorly around them from the left), a relationship of major surgical significance in pancreatic head resections.
• Splenic vessels: The splenic artery runs along the superior border of the pancreatic body/tail (often tortuous), giving off pancreatic branches; the splenic vein runs along the posterior surface of the body/tail, receiving pancreatic tributaries before joining the SMV to form the portal vein.
• Stomach: Lies anterior to the pancreas (separated by the lesser sac), forms part of the "stomach bed"; this relationship explains the classic finding of pain radiating through to the back in pancreatitis, given the retroperitoneal, posteriorly-fixed position of the gland directly behind the stomach and against the vertebral column.

Blood supply:

• Superior pancreaticoduodenal arteries (anterior and posterior), branches of the gastroduodenal artery (from the common hepatic artery, coeliac trunk), supplying the head (foregut-derived portion, reflecting the pancreatic head's embryological origin alongside the proximal duodenum).
• Inferior pancreaticoduodenal arteries (anterior and posterior), branches of the SMA, supplying the lower head/uncinate process (midgut-derived boundary, mirroring the duodenal foregut/midgut watershed at the major papilla level).
• Splenic artery branches: multiple small pancreatic branches (including the dorsal pancreatic, great pancreatic, and caudal pancreatic arteries) supplying the neck, body, and tail.
• The anterior and posterior pancreaticoduodenal arcades (superior + inferior) anastomose around the head, forming a similar collateral arcade principle to the small intestine, providing rich collateral supply to this region, though the more distal body/tail (splenic artery-dependent) has comparatively less collateral protection.

Venous drainage:

• Mirrors the arterial supply: pancreaticoduodenal veins drain to the SMV/portal vein directly; body/tail venous drainage is via small tributaries into the splenic vein, which runs along the posterior pancreatic surface before joining the SMV to form the portal vein.

Lymphatics:

• Drain to pancreaticosplenic and pancreaticoduodenal nodes along the corresponding vessels, converging on coeliac and superior mesenteric nodes: reflecting the gland's mixed foregut (head)/midgut boundary embryological origin.

Innervation:

• Parasympathetic (vagus, via coeliac plexus) and sympathetic (splanchnic nerves, via coeliac and superior mesenteric plexuses/ganglia), pain is typically severe, poorly localised epigastric pain with characteristic radiation through to the back, given the gland's deep retroperitoneal position and rich autonomic innervation shared with adjacent major plexuses.

Position:

• Lies in the left hypochondrium, tucked beneath the left costal margin, related to ribs 9-11 posterolaterally, normally impalpable given this protected position (a palpable spleen suggests splenomegaly, typically at least 2-3x normal size before becoming clinically detectable).

Surfaces:

• Diaphragmatic surface: Convex, smooth, related to the diaphragm and (via it) the left lung base/pleura and lower ribs.
• Visceral surface: Concave, related to the stomach (gastric impression), left kidney (renal impression), and splenic flexure of colon (colic impression).

Borders:

• Superior border: Often notched (a normal anatomical variant, sometimes palpable and used to distinguish an enlarged spleen from other left upper quadrant masses on examination).
• Inferior border: Smoother, related to the colic impression.

Hilum:

• Located on the visceral surface, where the splenic vessels (artery and vein) and lymphatics enter/exit, within the splenorenal (lienorenal) ligament; the tail of the pancreas often reaches close to (or into) the hilum within the same ligament.

Ligaments:

• Gastrosplenic ligament: Connects the spleen to the greater curvature of the stomach, containing the short gastric vessels and the left gastro-omental (gastroepiploic) vessels.
• Splenorenal (lienorenal) ligament: Connects the spleen to the posterior abdominal wall/left kidney, containing the splenic vessels and the tail of the pancreas.
• Phrenicocolic ligament: Connects the splenic flexure of the colon to the diaphragm, indirectly supporting the spleen from below (forming a "shelf" the spleen partly rests upon), not a direct splenic attachment but functionally relevant to splenic position and to the relatively deeper left paracolic gutter mentioned in Section 4.
• These two peritoneal ligaments (gastrosplenic and splenorenal) together suspend the spleen and, along with the lesser sac's boundaries, define the spleen's relationship to the greater and lesser peritoneal sacs (the spleen essentially lies at the left lateral extent of the lesser sac).

Relations:

• Stomach (anteromedially, via the gastrosplenic ligament), left kidney (posteromedially, via the splenorenal ligament), splenic flexure of colon (inferiorly), diaphragm and left lower ribs (laterally/posteriorly), the intimate rib relationship explains the association between lower left rib fractures and splenic injury in blunt abdominal/thoracic trauma.

Splenic vessels:

• Splenic artery: the largest branch of the coeliac trunk, characteristically tortuous, running along the superior border of the pancreas before dividing into multiple branches (typically 5-6) entering the hilum, this multi-branch terminal pattern creates a segmental blood supply within the spleen, allowing partial splenectomy in select cases.
• Splenic vein: runs along the posterior surface of the pancreas, receiving the inferior mesenteric vein (in most individuals) before joining the SMV to form the portal vein.

Splenic rupture:

• The spleen is the most commonly injured intra-abdominal organ in blunt abdominal trauma, given its relatively fragile capsule, rich vascularity, and fixed position against the lower left ribs, often associated with lower left rib fractures (9-11), which should raise clinical suspicion for underlying splenic injury.
• Can present with delayed rupture (a subcapsular haematoma initially contains the bleeding, which can rupture through the capsule days later), a classically tested pattern requiring awareness in trauma follow-up.
• Splenic injury classification and management (observation vs splenic artery embolisation vs splenectomy) depend on the grade of injury, reflecting the extent of capsular/parenchymal/vascular disruption.

Pancreatic tumour relations:

• Head of pancreas tumours classically present with painless obstructive jaundice, given the head's intimate relationship with the intrapancreatic portion of the common bile duct (compressed as it passes through/along the pancreatic head), a key distinguishing clinical presentation from tumours of the body/tail, which tend to present later (often with pain, weight loss, or metastatic disease) given their lack of a similarly obstructable adjacent structure.
• Body/tail tumours can invade or compress the splenic vein, potentially causing splenic (left-sided) venous hypertension and isolated gastric varices (a distinct entity from the more common oesophageal varices of portal hypertension, since this is a purely splenic venous outflow problem rather than a global portal hypertension).

Portal vein formation:

• Occurs directly posterior to the neck of the pancreas, from the union of the SMV and splenic vein: a critical relationship for understanding both pancreatic neck surgery risk and the pattern of portal hypertension development from pancreatic pathology compressing this confluence.