portal-systemic anastomoses

**Definition/physiology:** Normally, the portal vein carries splanchnic blood to the liver. In portal hypertension (portal pressure gradient >5 mmHg; varices form at ≥10 and bleed at ≥12 mmHg), resistance to portal flow causes blood to divert through preexisting low-pressure venous connections between portal and systemic (caval) tributaries. These collaterals dilate, but they cannot decompress the portal system fully and are prone to rupture.

**Key sites (high-yield):** 1. **Gastroesophageal junction:** Left gastric (coronary) vein (portal) → esophageal veins → azygos (systemic, SVC). Result: **esophageal varices** (submucosal, distal esophagus). Presents with painless, massive hematemesis. 2. **Anorectal junction:** Superior rectal vein (portal, via IMV) → middle and inferior rectal veins (systemic, via internal iliac and internal pudendal → IVC). Result: **internal hemorrhoids** (rectal varices). Note that hemorrhoids are not usually caused by portal hypertension, but they can be. 3. **Umbilicus:** Paraumbilical veins (portal, via the left portal vein/recanalized umbilical vein) → superficial and inferior epigastric veins (systemic, via the femoral/external iliac and the internal thoracic/superior epigastric veins). Result: **caput medusae**. A venous hum at the umbilicus is the **Cruveilhier-Baumgarten murmur**. 4. **Retroperitoneal/bare area of liver:** Colic veins (portal) → retroperitoneal (Retzius) veins (systemic); also splenorenal collaterals (splenic vein → left renal vein) and the bare area of the liver → diaphragmatic veins. Gastric varices can form via short gastric veins and gastrorenal shunts, and are seen especially in **splenic vein thrombosis** (isolated gastric varices).

**Causes of portal hypertension (by location):** - **Prehepatic:** portal or splenic vein thrombosis. - **Intrahepatic:** cirrhosis (most common in the US; presinusoidal, sinusoidal, or postsinusoidal), schistosomiasis (presinusoidal; periportal "pipestem" fibrosis), and others. - **Posthepatic:** Budd-Chiari syndrome, right heart failure, constrictive pericarditis, IVC webs.

**Clinical consequences:** Varices, splenomegaly/hypersplenism (thrombocytopenia), ascites (with the SAAG ≥1.1 g/dL), hepatic encephalopathy (ammonia and gut-derived toxins bypass hepatic detoxification via shunts), and hemorrhoids and caput medusae.

**Management of variceal bleeding:** Resuscitation (restrictive transfusion, Hb target ~7), IV octreotide (splanchnic vasoconstriction), IV ceftriaxone prophylaxis, and urgent endoscopy with band ligation. Primary and secondary prophylaxis: nonselective β-blockers (propranolol, nadolol, carvedilol), with or without endoscopic band ligation. Refractory bleeding: balloon tamponade (Blakemore/Sengstaken) as a bridge, or **TIPS** (transjugular intrahepatic portosystemic shunt, a hepatic vein to portal vein shunt). The main complication of TIPS is hepatic encephalopathy. Surgical shunts (e.g., distal splenorenal) are now rarely used.

**Mnemonic:** "Varices of GUTT": **G**astroesophageal (left gastric/azygos), **U**mbilical (paraumbilical/epigastric), **T**he rectum (superior/middle-inferior rectal), and **R**etroperitoneal. Alternatively, the "Rule of 1, 3, 8, 10, 2, 5": the root numbers of IMV/portal, etc. A simpler mnemonic: "Left gastric–Azygos, Superior rectal–Middle/Inferior rectal, Paraumbilical–Epigastric."

**Clinical pearls:** Caput medusae shows blood flowing **away** from the umbilicus (unlike IVC obstruction, in which the superficial veins of the abdominal wall show blood flowing **upward**, toward the SVC). Esophageal varices are a distinct entity from the Mallory-Weiss tear (retching, mucosal tear) and Boerhaave syndrome (transmural rupture).