Along with an exponential increase in awareness of venous disease has come a concomitant increase in its evaluation and treatment. Innovation from new drugs and novel devices specifically designed for the treatment of patients with venous disease has also driven this large increase in care that can be offered. Thus, a firm foundation in the knowledge of venous anatomy and physiology remains paramount to understanding what kinds of questions to ask throughout the evaluation process as well as to optimally apply proper treatment algorithms.

This chapter represents a brief overview of venous anatomy and physiology to give clinicians a solid foundation to apply to their everyday practice. The evolution of knowledge on this topic since Hippocrates’ first descriptions of venous ulcers around 400 BC has been vast.¹ Interestingly, although the facts of venous anatomy have come to a pinnacle in understanding, the topic often remains poorly misquoted, even by some of the most accomplished venous specialists. In contrast, knowledge of venous physiology and flow dynamics remains rudimentary at best despite the many advances in the treatment of patients with venous disease. Nevertheless, increased interest continues, and new discoveries are being made every day that will further the health of millions of individuals who are affected by acute and chronic diseases of the veins.

Basics

Three distinct layers make up the tubular structure of the vein wall. These are the tunica intima, the tunica media, and the tunica adventitia.² A single layer of endothelial cells lines the tunica intima. Depending on the type, location, and size of the vein, the tunica media varies considerably in the amount of smooth muscle and elastic fibers. The largest veins that include the superior and inferior vena cavae are almost completely void of smooth muscle fibers. Large veins such as the femoral or axillary veins have slightly more smooth muscle fibers. Medium-sized veins have a thicker layer of elastic fibers in association with circumferential smooth muscle fibers. These veins also have a thick layer of elastic fibers called the internal elastic lamina at the base of the tunica intima. Venules as well as most superficial veins such as the great saphenous vein have large amounts of smooth muscle fibers. These veins also lack an internal elastic lamina. There is little demarcation between the tunica media and the tunica adventitia. The tunica adventitia contains adrenergic nerve fibers and vasa vasorum in a bed of loose connective tissue. Figure 1-1 illustrates a cross-section of a medium-sized vein.

Unique to the anatomy of veins is the presence of one-way valves to assist in directing blood flow back to the heart. Venous valves are made up of a bilayer of connective tissue, tunica intima, and endothelial cells. This bicuspid anatomic formation is extremely strong given its thickness of 2 to 5 μm. Immediate to the anatomy of venous valves within each of the two cusps, the vein dilates, forming a sinusoid (Figure 1-2).

The cutaneous venous plexus forms a circulation network that ultimately directs blood to the deep venous system. The subpapillary venous plexus receives blood from the capillaries of the dermal papillae. Within the dermis, this plexus joins into a deeper reticular venous plexus, which in turn drains into superficial veins of the subcutaneous fatty layer. Figure 1-3 outlines this intimate network of venules.

Lower Limb

Variability as to the correct venous anatomic terminology of the lower limb continues to plague clinical medicine. Recognizing this, an International Interdisciplinary Committee updated the official Terminologica Anatomica in 2001.⁴ The document was further refined and extended in 2004.⁵

Pelvis and Abdomen

The common femoral vein becomes the external iliac vein after it crosses the inguinal ligament. The short trunk of the internal iliac vein joins the external just anterior to the sacroiliac joint to form the common iliac vein. The right and left common iliac veins converge at the level of the right lateral border of the fifth lumbar vertebrae to form the inferior vena cava. The inferior vena cava receives many important tributaries as it travels superiorly to the diaphragmatic hiatus on the right side of the vertebral column (Figure 1-4).

Although the embryology of the venous system is beyond the scope of this chapter, there are many variations of the inferior vena cava and renal veins that can have important clinical implications. About 2% to 3% of the time, double inferior vena cavae occur. Other anomalies of the inferior vena cava are less prevalent (Figure 1-5). More common renal vein anomalies include a renal vein collar (1%–9%) and a left posterior (retroaortic) renal vein (1%–2%) (Figure 1-6). Important clinical implications for these vena cava and renal vein variations include the placement of an inferior vena cava filter and aortic surgery, respectively.