Lymphedema is a chronic inflammatory condition that develops as a result of lymphatic insufficiency. Lymphatic insufficiency occurs from a decrease in reabsorption or a decrease in transport capacity of the lymphatic system. It can be primary malformation of the lymph system or an acquired condition due to obstruction or damage to the system (TABLE 5-1).

The lymphatic system is interrelated with all of the other systems of the body. Its primary roles include conducting immune system surveillance, assisting the cardiovascular system to maintain fluid homeostasis, and aiding the digestive system in the breakdown of long-chain fatty acids. The immunological functions involve both the immediate response to pathogens and the long-term resistance to repeated exposure to pathogens.

The body’s immunological function is performed by the lymphoid organs, including the spleen, thymus, tonsils, Peyer’s patches located in the small intestine, bone marrow, and lymph nodes (FIGURE 5-1).

The lymphatic system is a body-wide network of superficial and deep vessels connected by perforating vessels, similar to the venous system. It is comprised of lymph capillaries, lymphatic precollectors, collectors, ducts, and trunks (FIGURE 5-2). The superficial vessels, located directly under the skin and above the fascia, drain the dermis and subcutaneous tissues. The deep vessels are located below the fascia and drain all the tissue deep to the fascia. There are connecting vessels that perforate the fascia to transport the fluid from the deep vessel system to the superficial vessel system, which is the opposite of how the venous system functions. The lymphatic vessels are similar to arteries in that the larger collecting vessels have smooth muscle in the wall, and they are similar to the veins in that the collecting vessels contain valves that allow for unidirectional flow of the fluids.

The superficial system begins with the lymphatic capillaries that appear much like a fishnet underneath all of the skin (FIGURE 5-3). The capillaries are the smallest-diameter vessels and thus have the largest numbers. As the diameter of the more proximal lymphatic vessels increases, the number of lymphatic vessels decreases. Lymph capillaries have anchoring filaments that attach to the basement membrane between the dermis and epidermis (FIGURE 5-4). The lymph capillaries are more permeable than the vascular capillaries and therefore can absorb larger molecules of protein and fat. Each lymph capillary is composed of a single layer of overlapping flat endothelial cells, and the overlapping junction is called the inlet junction. The capillary does not contain valves, thus allowing the fluid to move in any direction within the capillary system.

The capillaries merge and become precollectors, which have a larger diameter and therefore a lower pressure, thus facilitating movement of the fluid from the capillary to the precollector. The precollectors also have the overlapping endothelial anatomy that allows them to absorb interstitial fluid, and they have both a limited number of valves and a limited smooth muscle structure that allows them to initiate transportation of the collected fluids.

All of the precollectors merge to become larger diameter vessels, termed collectors. The collectors first bring the lymph fluid to the lymph nodes and then carry the remaining fluid to the larger lymphatic trunks. The anatomical structure of the collectors is similar to the construction of the veins in that they have three distinct layers (intima, media, and adventitia). They have well-defined valves that permit flow to go in only one direction—toward the heart. Within the lymph collector, the vessel segment between two valves is termed the lymphangion (FIGURE 5-5). Each lymphangion has an autonomic-driven resting contraction rate of approximately 10–12 contractions per minute.¹ This is further discussed under physiology. The superficial lymphatic collectors are located in the subcutaneous fatty hypodermis and they follow a direct route toward the regional lymph nodes. The deep lymphatic collectors follow the pathway of larger blood vessels. Lymph collectors drain lymph fluid from specific areas of the body, creating lymphatic “territories” that drain to specific regional lymph nodes. These lymphatic territories are defined by lymphatic watersheds that tend to delineate the body into specific collection and drainage patterns (FIGURE 5-6). Although there is some cross-connection between the territories via the watersheds, most of the fluid flows directly to its own regional lymph nodes. If there is fluid overload in one area, some of the fluid can be diverted to another region via the watershed connections.

The lymph nodes (estimated to be about 700) are located in clusters throughout the body (FIGURE 5-7). The lymph node is bean-shaped and surrounded by a dense fibrous capsule (FIGURE 5-8). The collectors converge at the convex side of the lymph nodes where they are termed afferent lymph vessels. The fluid moves through the cortex of the node, into the medulla, and exits on the concave side via efferent vessels that then become trunks. The number of efferent vessels is less than the number of afferent vessels, resulting in a decreased transportation rate through the lymph nodes, and thus allowing the immune system cells time to phagocytose the pathogens that are in the lymphatic fluid.

When the superficial and deep collectors converge, the vessels are termed trunks. The trunks are similar in construction to the collectors except they are larger in diameter and contain more smooth muscle in the vessel wall (FIGURE 5-9). The trunks are named as follows: right and left lumbar trunks, gastrointestinal trunk, jugular trunk, supraclavicular trunk, subclavian trunk, peristernal trunk, and bronchial-mediastinal trunk. The right and left trunks and the gastrointestinal trunk converge in the anterior area of T-11-L2 to form the cisterna chyli, which is the beginning of the thoracic duct. The thoracic duct ascends cephalically along the anterior vertebral column and perforates the diaphragm.

The only direct connection between the lymphatic system and the venous system occurs where the thoracic duct (on the left) and the right lymphatic duct enter the venous angles. The venous angle is formed by the convergence of the internal jugular and subclavian veins (FIGURE 5-10). This is the anatomical termination of what is described as the lymphatic system.

The purpose of the lymphatic capillaries is to absorb interstitial fluid and molecules, and when the fluid enters the capillaries, it is termed lymphatic fluid. The endothelial cell junctions overlap, creating inlet valves, so that when the interstitial protein concentration increases, tension on the anchoring filaments causes the inlet valves to open and allows absorption of the larger fat and protein molecules. These inlet valves remain open as long as the interstitial pressure (a result of plasma protein concentration) remains higher than the pressure within the lymph capillary.

Fluid movement between the capillaries (arterial, venous, and lymphatic) and the interstitial spaces is governed by Starling’s Law of Equilibrium. This law describes how the osmotic and hydrostatic pressures in the capillaries and interstitial tissue determine the direction of fluid movement. The irony of this equation is that equilibrium is never really achieved because of the dynamic nature of the human body, which does not allow the pressure gradient to equal zero; therefore, fluid is always moving, or in physiologic terms, fluid is constantly being filtrated and reabsorbed at the capillary bed (FIGURE 5-12).^2,3

The difference between the net hydrostatic pressure and the net osmotic pressure is the force that determines the direction of fluid flow (TABLE 5-2). When the fluid flows from the interstitial space into the capillaries, it is termed reabsorption and can occur at both the venule and the lymphatic capillaries. When the fluid flows from the capillaries into the interstitial space, it is termed filtration. Equilibrium occurs when an equal amount of fluid moves from the arterial capillaries into the interstitial space and out of the interstitial space into the venous and lymphatic capillaries. Hydrostatic pressure is the pressure exerted by the blood on the capillary walls. Because the pressure is higher on the arterial side than on the venule side, fluid is pushed out of the capillary bed into the interstitial space. Osmotic pressure is the force created by large molecules such as plasma proteins, and it opposes hydrostatic pressure. Plasma protein molecules attract water, so that in a normal system they facilitate reabsorption of the fluids back into the venule.⁴

The blood capillary wall is a semipermeable membrane, thus a force is required to move the larger protein molecules in and out of the capillary bed. At the arterial end where the net hydrostatic pressure is higher than the net osmotic pressure, the molecules are forced out of the capillary bed and into the interstitium. However, at the venule end the net osmotic pressure is higher than the net hydrostatic pressure so the pressure is not sufficient to move the molecules from the interstitium into the capillary bed. Therefore, the molecules are reabsorbed into the lymphatic capillary at the overlapping endothelial junction. When this process is in balance so that fluids are adequately moved, no edema occurs. When there is an imbalance, for a variety of reasons and in either direction, edema develops. All edema pathology can be related to a problem with either filtration or reabsorption. When this happens, there is a transportation dysfunction—the freeway is clogged. The challenge to the clinician is to determine the pathology that prevents adequate flow of the fluid back into the central vascular system.

Primary lymphedema is a result of congenital malformations of the lymphatic system, although the consequences may not be observed in the early years (FIGURES 5-13 and 5-14). Secondary lymphedema is a result of acquired damage to the lymph vessels or nodes and subsequent impaired reabsorption and/or transportation of lymphatic fluid (FIGURE 5-15). Refer to TABLE 5-1 for more details of both types.

A frequent cause of secondary lymphedema is chronic venous insufficiency (FIGURE 5-16).^5,6 The sequence of events is as follows: The venous system becomes compromised and cannot accommodate the normal amount of venous flow. The lymphatic system, when healthy, can compensate because it can increase its rate of lymphangion contraction up to 10 times its resting volume and transport the fluid normally carried by the venous system.¹ For edema to develop in patients with chronic venous insufficiency, one of two scenarios must occur. Either the lymphatic and venous load exceeds the maximum transport capacity of the lymphatic system or the lymphatic system becomes impaired and cannot transport the usual fluid load. The lymphatic impairment may be caused by incompetent lymphatic valves due to distended vessels.^7,8

In the United States, the most recognized cause of lymphedema is related to cancer and its treatment (FIGURE 5-17).⁹ The location and the severity of oncology-related lymphedema are influenced by the area affected, the location and total dosage of radiation, the extent of lymph node dissection, obesity, and presence of co-morbidities.^10,11 Clinical presentation can vary drastically and treatment has to be individualized. Other causes of secondary lymphedema include trauma, infection, surgery in which the lymphatic vessels are severed or damaged, and systemic disorders (eg, liver, kidney, or cardiac disease) (FIGURES 5-18 to 5-20). However, any pathology that results in damage to the lymphatic system with decreased transport capacity will result in chronic secondary lymphedema, and clinical presentation will be essentially the same with variations only in relation to the severity of the damage.