The lymphatic system varies a little in everyone: the number and size of lymph nodes, the number, exact location and specific direction of lymph vessels, and so on. When these variations become more extreme, a person can be at risk for lymphedema. Some of the problems found in primary lymphedema (whether hereditary or not) are as follows:
The initial lymphatics are the start of the lymphatic system. They are tiny finger like projections in the dermis. They have flap-like valves that open and close to allow tissue fluid, proteins, and other large molecules, cells, germs, and debris to enter. The initial lymphatics are arranged in a mesh in the skin all over the body. They lead to a network of pre-collectors which connect the initial lymphatics to the collecting vessels (lymph collectors).When there are too few initial lymphatics in a particular area of the body, the tissue fluid and its components, including protein, is not able to enter the lymphatic system. It stagnates in the tissues causing a high-protein edema.
The collectors are in the tissue just below the skin. They travel up the limb to the lymph nodes, which are located throughout the body. When there are not enough collectors, the lymph fluid gets backed up in the pre-collectors and can reflux out the initial lymphatics and into the tissues again.
Although it doesn’t seem as if this could be a problem, it is when the collectors become a tangled winding mass, not really leading anywhere.
The collectors are made up of units called lymphangions. At the beginning and end of each lymphangion is pair of valves which open to allow lymph fluid to pass from one lymphangion to the next and which prevents backflow of lymph fluid.
With an enlarged collector, these valves may not be able to meet and close. If the valves can’t work, then instead of lymph fluid moving to the nodes, it can also move backwards and reflux into the tissues.
Too few lymph nodes or malformed nodes. The purpose of the nodes is to filter the lymph fluid, removing and destroying anything that is harmful, before the lymph fluid is returned to the bloodstream. A blockage here will back fluid up through the collectors which become distended and incompetent. This eventually leads to reflux into the tissues which results in swelling.
An examination of 46 people with primary lymphodema of the leg (Fox et al) found that 41/46 had problems in the lymph nodes located behind the knee. These were found to be hardened and malformed. This would seriously affect lymph flow from the calf and lateral ankle.
A lack of functional nodes would also affect the effectiveness of the immune system, leaving the person more prone to infections. A vicious cycle can begin. Persistent local infections of a limb can damage or destroy lymph collectors and eventually the lymph nodes. It can make the tissue in the area of the infection hard and fibrotic.
This leads to less fluid being carried to the nodes and fewer nodes to filter it, thus hastening the onset of lymphedema or worsening it.
There are also initial lymphatics (called lacteals) and collectors in the intestinal tract and the other organs. The collectors mostly go to the largest lymph trunk in the body, the thoracic duct.
Along the way from the abdomen, the lymph is filtered by numerous nodes. The thoracic duct carries not only the lymph from the various organs but also lymph from both legs, the lower trunk of the body, and the upper left half of the body, including left arm and left side of the head.
A problem with the abdominal lymphatics or with the thoracic duct can have much more serious consequences than lymphedema of the limb. It can lead to conditions of chylous reflux (the backflow of lymphatic fluid from the intestines to other areas of the body) and protein-losing enteropathy (PLE). In PLE instead of plasma proteins being returned to the blood stream, they are lost in the intestinal tract and excreted. This leads to a lymphedema of the intestinal wall and a generalized swelling of the body. It is a critical condition which requires medical intervention and a special diet.