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MiscellaneousStandardLast updated 29 May 2026

Anatomy

The retroperitoneum is the operative home of the kidneys, ureters, adrenals, and the great vessels. This tab covers its boundaries and contents, the posterior abdominal wall, the overlying gastrointestinal viscera, and the arterial, venous, lymphatic, and nervous structures that run through it.

Boundaries and Contents

The retroperitoneum is bounded anteriorly by the posterior peritoneal reflection, posteriorly by the abdominal wall, cranially by the diaphragm, and caudally by the extraperitoneal pelvic structures (bladder, rectum, vagina, uterus). (The extraperitoneal pelvic structures differ from the extraperitoneal space, which also includes the retroperitoneum and the space circumferentially surrounding the abdominal cavity.)

  • Organs — primarily retroperitoneal: kidneys, ureters, adrenal glands. Secondarily retroperitoneal: the 2nd and 3rd duodenum, ascending colon, descending colon, and pancreas.
  • Vessels — abdominal aorta and branches, IVC and tributaries, ascending lumbar veins, portal vein, lumbar lymph nodes and trunks, and the cisterna chyli.
  • Nerves — branches of the lumbosacral plexus, the sympathetic trunk, and the autonomic plexuses and ganglia.

Posterior Abdominal Wall

  • Flank muscles (layers): skin, subcutaneous fascia, external oblique (its inferior aponeurotic border forms the inguinal ligament), internal oblique, transversus abdominis, and transversalis fascia (which crosses the midline anteriorly, fuses with the lumbodorsal fascia posteriorly, and is continuous with the endopelvic fascia). They flex, extend, and rotate the trunk and compress the abdominal contents.
  • Deep muscles — psoas major (along the pelvic brim, posterior to the inguinal ligament), psoas minor (hip flexion; L1–L3; may be absent), iliacus (hip flexion), quadratus lumborum (posteromedial to psoas), and erector spinae.
  • Spine — 7 cervical, 12 thoracic, 5 lumbar vertebrae, sacrum, and coccyx. The cord terminates as the cauda equina at vertebral level L2. Critically, spinal-cord segmental levels do not match vertebral levels — e.g. the C8 segment lies at the C7 vertebra and the T12 segment at the T8 vertebra. The conus medullaris is the bulbous distal cord (continuing as the filum terminale); the cauda equina is the horsetail of nerve roots distal to it. Always specify vertebral column level versus spinal segmental level when describing spinal cord injury.
  • Lower ribs — the 10th–12th ribs protect the retroperitoneum, so a lower-rib fracture should raise suspicion for retroperitoneal injury. The 11th and 12th are "floating" ribs (no anterior sternal attachment). Intercostal vessels and nerves run in the costal groove on the caudal margin of the superior rib.
  • Lumbodorsal fascia — three layers covering the posterior musculature (posterior lamella over erector spinae, middle lamella separating it from quadratus lumborum, anterior lamella over quadratus lumborum continuous with psoas fascia). A dorsal lumbotomy enters the retroperitoneum without cutting muscle, via a vertical incision lateral to the erector spinae and quadratus lumborum.

Gastrointestinal Viscera

  • Pancreas — the head lies anterior to the IVC within the C-loop of the 2nd duodenum (at risk in right kidney surgery); the tail abuts the spleen and the left upper pole/adrenal (at risk in left kidney surgery). The stomach overlies the left upper pole during transperitoneal left renal surgery.
  • Duodenum (20–25 cm) — mobilised by a Kocher manoeuvre to expose the right retroperitoneum. The 1st part is intraperitoneal; the 2nd (descending) part is retroperitoneal and adjacent to the right renal hilum (the common bile and pancreatic ducts enter at the ampulla of Vater); the 3rd part crosses behind the SMA and in front of the aorta; the 4th part becomes intraperitoneal at the jejunum.
  • Colon — the ascending colon/hepatic flexure overlie the right retroperitoneal structures and the splenic flexure/descending colon the left. Transperitoneal renal access requires reflecting the colon medially at the white line of Toldt, dividing the hepatocolic/splenocolic ligaments sharply to avoid liver or spleen injury.

Arterial Supply

Arteries have three layers — tunica intima, media, and externa (adventitia). The abdominal aortic branches, superior to inferior:

  • Inferior phrenic arteries (paired) — supply the diaphragm; give off the superior adrenal arteries.
  • Celiac artery — gastric, splenic, and common hepatic branches; supplies the foregut organs.
  • Middle adrenal arteries (paired) — at or above the SMA.
  • Superior mesenteric artery (SMA) — at L1–L2; branches are the inferior pancreaticoduodenal, ileocolic, right colic, and middle colic. The middle colic anastomoses with the left colic (IMA) via the marginal artery of Drummond, allowing the IMA to be sacrificed — but SMA injury in left retroperitoneal surgery causes severe bowel ischaemia.
  • Renal arteries (paired, L1) — give off the inferior adrenal arteries.
  • Gonadal arteries (paired) — the testicular arteries run anterior to the psoas, IVC, genitofemoral nerve, and ureter toward the internal ring; the ovarian arteries run anterior to the ureter through the infundibulopelvic ligament. Extensive collaterals permit ligation without gonadal ischaemia.
  • Lumbar arteries (4 paired) — supply the posterior body wall and spine.
  • Inferior mesenteric artery (IMA) — left colic, sigmoid, and superior rectal branches (splenic flexure to upper rectum). The superior rectal anastomoses with the middle rectal (internal iliac) and inferior rectal (internal pudendal) — an internal-iliac-to-IMA collateral that protects the rectum during IMA ligation.
  • Middle sacral artery — from the posterior aorta before the bifurcation.

Venous Drainage

The IVC forms from the common iliac veins, to the right of and below the aortic bifurcation; the venous system is far more variable than the arterial.

  • Tributaries — the median sacral vein (drains into the left common iliac vein); the ascending lumbar veins (which become the azygos on the right and hemiazygos on the left); the gonadal veins; and the renal veins.
  • Gonadal veins — the left testicular/ovarian vein enters the left renal vein at a right angle, while the right enters the IVC directly (the right testicular vein enters the right renal vein in ~10%). The left vein's length and perpendicular entry explain the higher incidence of left varicocele; a sudden right-sided varicocele should prompt retroperitoneal imaging for an obstructing malignancy.
  • Renal veins — anterior to the renal arteries, draining into the IVC at L1. The right is short with no tributaries; the left is long and receives the left gonadal vein inferiorly, a lumbar vein near the gonadal ostium, and the left adrenal vein superiorly.
  • Portal system (does not mirror the arteries) — the splenic vein drains the colon distal to the splenic flexure (and receives the inferior mesenteric vein); the SMV drains the small bowel and proximal colon and joins the splenic vein to form the portal vein; the hepatic veins enter the anterior IVC (occlusion → Budd-Chiari syndrome).

Lymphatics

Lymph flows cephalad and right-to-left, returning to the venous system at the left innominate (brachiocephalic) vein. Pelvic and lower-limb lymph passes through the internal/external/common iliac, obturator, and sacral nodes up to the lumbar nodes. The lateral lumbar nodes' efferents form the lumbar trunks, which meet at the cisterna chyli (anterior to L1–L2, right of the aorta) — the start of the thoracic duct, which ascends behind the aorta to the left innominate vein.

Nervous System

The retroperitoneal nerves are autonomic (to viscera, vessels, smooth muscle) and somatic (to skeletal muscle, skin, peritoneum). The autonomic system uses a pre-ganglionic neuron (cell body in the CNS) synapsing on a post-ganglionic neuron — except the adrenal medulla, where pre-ganglionic fibres synapse directly on chromaffin cells.

  • Parasympathetic — pre-ganglionic fibres from cranial nerves III, VII, IX, X (the vagus supplies thoracic, abdominal, and pelvic viscera) and from S2–S4 (the pelvic splanchnic nerves); post-ganglionic neurons lie in the viscera walls.
  • Sympathetic — pre-ganglionic fibres from T1–L2 enter the sympathetic trunk (medial to the psoas), then either synapse in the trunk or pass as splanchnic nerves to one of the aortic plexuses: the celiac plexus (largest; much of the autonomic supply to kidney, adrenal, renal pelvis, and ureter), the superior hypogastric plexus (disruption → loss of seminal-vesicle emission or bladder-neck closure → retrograde ejaculation), and the contiguous inferior hypogastric plexus. (Thoracic, lumbar, and sacral splanchnics carry sympathetic fibres; pelvic splanchnics carry parasympathetic fibres.)
  • Somatic — the lumbosacral plexus arises from the lumbar and sacral anterior rami plus T12. The subcostal nerve (T12) runs below the 12th rib. The sciatic nerve (L4–S3) supplies most of the lower limb and is at risk from prolonged hip hyperflexion in the high lithotomy position.