Abdominal Vasculature: Inferior Vena Cava and Portal Venous System

This set covers the anatomy, physiological respiratory responses, tributaries, and common pathologies of the Inferior Vena Cava and the Portal Venous System as discussed in the lecture notes.

Inferior Vena Cava (IVC)

A large retroperitoneal vessel that drains the lower body and hepatic veins, ascending on the right side of the aorta.

IVC Formation

Formed by the union of the common iliac veins (CIV) posterior to the right common iliac artery (CIA) at the level of $L5$.

IVC Termination

The IVC pierces the central tendon of the diaphragm at the level of $T8$ to enter the right atrium of the heart.

Inspiration effect on IVC

The IVC diameter decreases (collapses) because negative pressure in the chest pulls more blood into the heart.

Expiration effect on IVC

The IVC diameter increases (distends) because venous return to the heart decreases slightly, allowing the vessel to fill.

Hepatic Veins

The largest visceral tributaries of the IVC, returning deoxygenated blood from the liver; they include the right, middle, and left hepatic veins.

Right Hepatic Vein (RHV)

Drains the right lobe of the liver and empties posteriorly into the IVC.

Middle Hepatic Vein (MHV)

Drains the caudate lobe of the liver and may fuse with the left hepatic vein before entering the IVC.

Left Hepatic Vein (LHV)

Drains the left lobe of the liver and often joins the middle hepatic vein before entering the IVC.

Left Renal Vein (LRV)

Arises from the renal hilum and flows posterior to the Superior Mesenteric Artery ($SMA$) and anterior to the aorta to enter the IVC.

Right Renal Vein (RRV)

Flows directly from the right renal hilum into the posterolateral aspect of the IVC; it is typically shorter than its left counterpart.

Portal Venous System

Also known as the hepatic portal system, it carries nutrient-rich, deoxygenated blood from the GI tract, spleen, and pancreas to the liver.

Main Portal Vein Formation

Formed posterior to the pancreas by the union (confluence) of the superior mesenteric vein and splenic vein; the trunk is $5$ to $7\,cm$ in length.

Portal Triad

A grouping of a branch of the portal vein, hepatic artery, and bile duct within a connective tissue sheath, giving the portal vein an echogenic wall.

Splenic Vein

A tributary of the portal circulation that runs along the posteromedial border of the pancreas, beginning at the hilum of the spleen.

Superior Mesenteric Vein (SMV)

Drains blood from several smaller veins including the middle colic and right colic veins, joining the splenic vein to form the main portal vein.

Inferior Mesenteric Vein (IMV)

Drains the left third of the colon and upper colon (distal colon and rectum) and most commonly drains into the splenic vein.

Bunny Sign

The sonographic appearance of the hepatic veins as they join the IVC in a transverse view, where the veins represent the ears and the IVC the head.

IVC Thrombosis

The most common serious pathology of the IVC, characterized by echogenic material in the lumen and a noncompressible vessel, often extending to renal or iliac veins.

IVC Filter

A transvenous filter placed into the IVC to prevent recurrent pulmonary embolization in patients who cannot tolerate anticoagulants.

IVC Dilation Causes

Includes right-sided heart failure, congestive heart failure ($CHF$), tricuspid regurgitation, and pulmonary hypertension.

IVC Compression Factors

Mechanical narrowing caused by pregnancy, retroperitoneal tumors, lymphadenopathy, abdominal aortic aneurysm ($AAA$), or hepatomegaly.

Circumaortic Left Renal Vein

An IVC congenital variant where the left renal vein has components passing both anterior and posterior to the aorta.

Nutcracker Anatomy

The position of the left renal vein as it passes between the aorta and the superior mesenteric artery.