Chapter 11: Portal Venous System

Portal Venous System

Carries blood and nutrients from the bowel and abdominal organs to the liver for metabolism and detoxification; includes all veins that drain blood from the spleen, pancreas, gallbladder, and gastrointestinal tract, with the exception of the lower rectum; blood is then delivered to the liver by the portal vein; disruption to the flow can cause adverse effects; includes the SMV, SPV, IMV, main portal vein, right portal vein, and left portal vein; walls appear brighter on U/S b/c of their high collagen content and sheath covering

Main Portal Vein (MPV)

Formed by confluence of splenic vein (SPV) and the SMV; forms posterior to neck of the pancreas and anterior to IVC; courses superior and to the right, ascending to liver hilum, then divides into right and left branches; along the course, runs posterior to and between the CBD and hepatic artery (artery medial to CBD); normal diameter should not exceed 1.3cm; Texas T sign appearance on scan

Left Portal Vein (LPV)

Longer and narrower than right; courses horizontally to the left; divides into medial (umbilical) and lateral (transverse) segments that further branch out to feed the medial and lateral left lobes of liver and caudate lobe; best seen on transverse

Right Portal Vein (RPV)

Branches into anterior and posterior segments that further branch in the right lobe of the liver; some branches also feed caudate lobe (only lobe fed by both the RPV and LPV)

Splenic Vein

Drains spleen; courses lateral to medial posterior to pancreas; joins SMV to form portal vein

Superior Mesenteric Vein (SMV)

Drains small intestine and portion of large intestine; courses from inferior to superior

Inferior Mesenteric Vein (IMV)

Drains large intestine; courses inferior to superior

Portal Venous System Physiology

Drain blood from the abdominal organs and bowel; deliver it to the liver for metabolism and detoxification; portal veins terminate in the liver in sinusoids or capillary-like vessels that deliver blood to the hepatic veins and, in turn, to the inferior vena cava; portal venous blood filtered twice, first in capillaries of pancreas, spleen, GB, and GI, then second in liver sinusoids

Sonographic Appearance of Portal Venous System

Anechoic tubular structure, bright echogenic wall margins; portal triads: formed by arteries, bile ducts, and portal veins, enclosed by sheath of connective tissue, spontaneous, phasic hepatopetal (towards the liver) blood flow

Sonographic Application/Lab Values

Used to detect portal vein hypertension (most common reason for PV exam), tumor invasion, or a thrombosis; laboratory values do not directly indicate portal vein pathology; a tumor, or cirrhosis of the liver, however, will produce various laboratory and clinical data that could point to portal vein involvement

Associated Tests

Duplex Doppler sonography primary tool (used in U/S)

Color Doppler imaging (used in U/S)

Direct portal venography

Computed axial tomography