retroperitoneal organs

**Definition:** Retroperitoneal organs sit behind the parietal peritoneum of the posterior abdominal wall. Unlike intraperitoneal organs, they have no mesentery and are only partially covered by peritoneum (anterior surface). Intraperitoneal organs (stomach, liver, spleen, jejunum/ileum, transverse and sigmoid colon, appendix, first part of duodenum, tail of pancreas) are suspended by mesenteries.

**Mnemonic: SAD PUCKER** - **S** – Suprarenal (adrenal) glands (primary) - **A** – Aorta / IVC (primary) - **D** – Duodenum (2nd–4th parts; secondary) - **P** – Pancreas (head, neck, body; tail is intraperitoneal in the splenorenal ligament; secondary) - **U** – Ureters (primary) - **C** – Colon (ascending and descending only; secondary) - **K** – Kidneys (primary) - **E** – Esophagus (lower/abdominal part) - **R** – Rectum (upper rectum is partly retroperitoneal; the lower part is subperitoneal)

**Primary vs. secondary:** - *Primary retroperitoneal:* developed in the retroperitoneum and never had a mesentery (kidneys, adrenals, ureters, aorta, IVC, rectum). - *Secondary retroperitoneal:* originally intraperitoneal with a mesentery, then displaced and fused to the posterior wall during rotation and growth, so the mesentery was lost (duodenum 2nd–4th parts, pancreas head/body, ascending/descending colon).

**Clinical significance:** - *Pancreatic cancer (head):* retroperitoneal location means silent growth, late presentation, back pain (posterior invasion/celiac plexus), and obstructive jaundice from compressing the common bile duct. - *Abdominal aortic aneurysm rupture:* can produce a retroperitoneal hematoma with hypotension and flank/back pain, with a relatively contained bleed. Anterior rupture into the peritoneum is catastrophic. - *Kidney/ureter trauma:* urine or blood collects in the retroperitoneum, so there may be no peritoneal signs on exam. Pain from stones is colicky and radiates flank to groin. - *Retroperitoneal bleeding:* flank ecchymosis (Grey Turner sign) and periumbilical ecchymosis (Cullen sign) in hemorrhagic pancreatitis. Also seen with anticoagulation or trauma. - *Duodenal rupture (blunt trauma):* can present subtly, because retroperitoneal air or fluid causes delayed peritonitis. CT may show retroperitoneal air. - *Retroperitoneal fibrosis (Ormond disease):* fibrous tissue encases the aorta and ureters, causing hydronephrosis. Associated with IgG4-related disease, methysergide, and malignancy. - *Psoas abscess and retroperitoneal sarcoma:* retroperitoneal masses are often large at diagnosis. - *Diagnostic imaging:* CT is preferred for retroperitoneal pathology. FAST exam does not reliably detect retroperitoneal bleeding. - *Surgical relevance:* Ascending/descending colon can be mobilized using the white line of Toldt, which is the peritoneal reflection at the fusion fascia. Kocher maneuver mobilizes the duodenum and pancreatic head.

**Embryology link:** Midgut rotation and fusion of the visceral peritoneum with the parietal peritoneum (fusion fascia of Toldt) create secondary retroperitoneal organs.