Chapter 24

### INTRODUCTION

In recent years, significant progress has been made in refining our understanding of the evolution and anatomy of the venous system. The exploration and identification of genes linked to growth factors that affect normal and abnormal development of blood vessels has spurred our insight into this field. Furthermore, rapid advances in ultrasound techniques and imaging protocols coupled with major strides in endovenous intervention have revolutionized the diagnosis and treatment of a variety of acute and chronic venous disorders. The old paradigms advocating conservative "observational" management of venous disorders appear to be rapidly falling away as the therapeutic pendulum in venous disease now swings from palliation toward cure.

This chapter discusses the embryology, histology, anatomy, and major clinical disorders affecting the inferior vena cava (IVC) and provides an overview of the clinical features, diagnosis, and treatment of caval disease.

### EMBRYOLOGY

In the seventh week of fetal gestation, the posterior cardinal veins, which drain the caudal portion of the fetus, begin to involute and form the subcardinal and supracardinal venous system.1 The infrarenal segment of the IVC arises from the caudal right supracardinal vein. The renal segment of the IVC arises from a venous network located around the aorta in a collar-like configuration, called the subsupracardinal anastomosis (the so-called renal collar). The anterior segment of the renal collar gives rise to the left renal vein. The suprarenal segment of the IVC arises from the right subcardinal vein, with the exception of the hepatic venous segment, which arises directly from the hepatic sinusoids.2

### HISTOLOGY

The walls of all veins are composed of three layers: intima, media, and adventitia. A combination of endothelial cells and a connective tissue layer make up the intima. Venous valves that are bicuspid in configuration are formed by the endothelium. The next layer is the internal elastic lamina (IEL), which are thick elastic fibers. The media, rich in collagen and smooth muscle cells, lies between the IEL and adventitia. The media of both the superior vena cava (SVC) and IVC are primarily composed of connective tissue. The adventitia consists of loose connective tissue with nerve fibers and is difficult to differentiate from the adjacent media, particularly in the respective vena cava. This outer layer protects and anchors the vessel to the surrounding tissues.3,4

### ANATOMY

The IVC begins at the junction of the right and left common iliac veins at the level of L4–L5 and ascends to the right of the aorta in the retroperitoneum. The IVC lies behind the head of the pancreas, the superior portion of the duodenum, and the portal vein. It traverses the diaphragm, coursing in a groove on the posterior hepatic surface, and then passes through the pericardium and enters the right atrium. The Eustachian valve is located on the lateral aspect of the IVC at the ...

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