Glossary

An important protein that helps keep fluid inside blood vessels and supports overall health.

An oral PI3Kα inhibitor approved by the FDA for treating PROS. Alpelisib reduces PIK3CA activation caused by a mutation and helps reduce overgrowth and malformation symptoms.

Growth of new blood vessels from the existing vasculature.

A rare vascular lesion characterized by diffuse proliferation of blood vessels with accompanying mature adipose tissue.

An irregularity or deviation from normal; an abnormal structure.

A tangle of abnormal arteries and veins that connect directly to each other (without the usual tiny capillaries in between). This can change blood flow and may cause pain, bleeding, or swelling.

The accumulation of fluid in the abdominal (peritoneal) cavity.

A test where a doctor removes a small sample of tissue or cells so it can be examined under a microscope.

A noninvasive breathing support machine that delivers air pressure through a mask—higher pressure when breathing in and lower pressure when breathing out.

A group of medications that slow bone breakdown and can help strengthen bones. They are often used to treat conditions that cause weak or fragile bones.

A descriptive term for microcystic isolated LM with small, blister-like swelling on the skin surface filled with clear or sometimes blood-tinged fluid. These can leak, bleed, or become infected.

A procedure in which a small sample of bone is removed and examined to diagnose bone disease or abnormalities.

A measurement of bone strength based on how much calcium and mineral content is present in a section of bone, usually assessed with an X-ray–based test.

Surgical procedure that replaces missing bone in order to repair bone fractures.

The ongoing process of breaking down and rebuilding bone.

A nuclear medicine imaging test that shows areas of abnormal bone activity, often used to detect fracture, infection, or tumors.

A series of x-rays of the entire skeleton or major portions of it.

A gene that helps regulate cell growth through the RAS/MAPK pathway. Certain BRAF mutations have been identified in vascular and lymphatic anomalies.

A tiny blood vessel that connects small arteries and veins. Capillaries allow oxygen, nutrients, and fluid to move between the blood and surrounding tissues.

A bacterial infection of the deeper layers of the skin that causes redness, warmth, swelling, and pain. It is most often caused by Streptococcus or Staphylococcus bacteria.

A complex lymphatic anomaly affecting the central lymphatic channels, such as the thoracic duct. It can cause lymphatic obstruction, leakage, chylous effusions, abdominal lymphatic dysfunction, and protein-losing enteropathy.

Involves the neck and chest.

A structural defect where part of the cerebellum extends downward into the spinal canal, which can affect cerebrospinal fluid flow.

Test to examine chromosomes in a sample of cells, which can help identify genetic problems as the cause of a disorder or disease.

Chyle is a milky-looking fluid that travels through your lymph system. But it’s made in your small intestine. It’s a mix of lymph and fats (lipoproteins). Chyle is how many of the fats that enter your digestive system get carried to your bloodstream.

A condition in which chyle—a fat-rich lymphatic fluid—leaks out of the lymphatic system into areas such as the chest or abdomen. It may occur due to lymphatic abnormalities, injury, or obstruction.

Chylothorax (also know as chylous effusion) is the accumulation of chyle, a milky bodily fluid, in the pleural cavity.

The presence of chyle in the peritoneal cavity as a result of anomalies, injuries, or obstruction of the thoracic duct.

A dilated sac at the lower end of the thoracic duct into which the intestinal trunk and two lumbar lymphatic trunks open.

A research study in humans that tests whether a medical treatment, drug or device is safe and effective.

An umbrella term referring to a group of rare and severe lymphatic disorders including GLA, GSD, KLA, CCLA, and GLD. These conditions involve abnormal lymphatic structure and function across multiple body regions including organs, tissue, and/or bones.

Use of medical-grade compression garments to reduce swelling, improve lymphatic flow, and control symptoms in lymphatic malformations or lymphedema. Often used as part of long-term symptom management rather than a cure.

Present at birth.

A problem with the structure of the heart that are present at birth; the most common type of major birth defect and can range from mild to life-threatening.

An imaging test that uses X-rays and a computer to create detailed “slice” pictures of the inside of the body.

A bluish color of the skin or lips caused by low oxygen levels in the blood. It can occur due to heart or lung disease or severe breathing problems.

An abnormal closed cavity or sac in the body, lined by walls called epithelium and containing a liquid or semisolid material.

A blood test marker that indicates the presence of recent or ongoing blood clot formation and breakdown in the body.

A low-dose X-ray test used to measure bone density and assess bone strength. It helps determine the risk of fractures and monitor bone health over time.

An advanced MRI technique that uses contrast dye to visualize lymphatic vessels in real time. It helps identify abnormal lymphatic flow, blockages, or leaks—especially in complex lymphatic anomalies.

A heart ultrasound test that uses sound waves to create moving images of the heart’s structure and function. It helps diagnose valve problems, heart defects, and heart pumping strength.

A buildup of fluid in a space in the body where fluid doesn’t normally collect, often due to inflammation, injury, infection, or drainage problems.

A minimally invasive procedure used to block abnormal blood or lymphatic vessels. In complex lymphatic malformations, embolization may be used in select cases, particularly when abnormal vessel connections, bleeding, or lymphatic leakage are present.

A procedure in which a flexible tube with a camera (endoscope) is inserted into the body to view internal organs such as the stomach, colon, or airways.

The main type of cell found in the inside lining of blood vessels, lymph vessels, and the heart. They are thin and flat.

A treatment that is still being studied to understand how safe it is and how well it works. It may be tested in clinical trials or used when standard options are limited.

Official permission from the U.S. Food and Drug Administration to market a drug for a specific medical use.

A period during which a patient's symptoms become more severe, frequent, or noticeable than their usual baseline.

A rare condition where lymphatic vessels grow abnormally in multiple areas of the body, such as the lungs, bones, or soft tissues. Symptoms vary and may include fluid buildup or breathing problems.

A condition in which the lymphatic system does not develop normally, leading to widespread lymphatic problems such as swelling (edema), fluid collections, or repeated infections.

A genetic change present in the egg or sperm that becomes incorporated into all cells of the body. Germline mutations are inherited across generations.

A rare disorder where abnormal lymphatic vessel growth in bone is linked to progressive bone loss. It can weaken bones and lead to pain, fractures, or deformity.

Histology is the study of the microanatomy of cells, tissues, and organs as seen through a microscope. It examines the correlation between structure and function.

The long bone of the upper arm that connects the shoulder to the elbow.

Swelling of one kidney due to a backup of urine that occurs with a disease. It is a sign of an underlying condition, not a disease itself.

A serious condition where abnormal fluid builds up in multiple areas of the body, often detected before birth.

A condition in which blood has high levels of fats such as cholesterol or triglycerides. It increases the risk of heart disease and stroke.

A condition in which albumin levels in the blood are lower than normal

A weakening of the immune system that occurs as a result of another condition, such as protein loss or lymphatic dysfunction, rather than from a primary immune disorder. It can increase susceptibility to infections.

The body’s natural response to injury or illness, causing redness, swelling, heat, and pain. In chronic lymphatic conditions, inflammation may contribute to disease progression and symptom flares.

A specialized imaging procedure in which contrast dye is injected directly into lymph nodes to map lymphatic vessels and flow. It is often used to diagnose chyle leaks or guide interventional treatments.

A rare and aggressive lymphatic disorder that often affects the chest, including the lungs and surrounding tissues. It can cause breathing problems, fluid buildup, bleeding or clotting abnormalities, and, in some cases, involvement of bones or other organs.

A gene that plays a key role in regulating cell growth and signaling pathways. Mutations in KRAS are associated with some complex lymphatic anomalies and related conditions.

Treatment using focused laser energy to shrink or seal abnormal lymphatic or blood vessels, commonly used for microcystic LM blebs or skin lesions.

Any abnormal area of tissue, such as a spot, wound, growth, or inflammation. Lesions can be benign or serious depending on the cause.

The surgical tying off of a blood vessel, lymphatic vessel, or other structure to stop flow or prevent leakage.

A specialized diet that limits long-chain fats and uses medium-chain triglycerides (MCTs), which are absorbed directly into the bloodstream rather than the lymphatic system. This diet is often used to reduce chyle production and manage chyle leaks.

A clear fluid that circulates through the lymphatic system, carrying white blood cells, proteins, and waste products. It helps maintain fluid balance and supports immune function.

A condition in which lymphatic vessels become abnormally enlarged and leaky, allowing lymph fluid to escape instead of flowing normally. When this occurs in the intestines, it can lead to problems such as nutrient and protein loss (protein-losing enteropathy).

The formation of lymphatic vessels from pre-existing lymphatic vessels, in a method believed to be similar to blood vessel development or angiogenesis.

An older imaging test in which dye is injected into lymphatic vessels to visualize them on X-ray. Rarely used today due to advances in lymphoscintigraphy and MRI.

A rare lung disease that leads to abnormal smooth-muscle–like cells grow in the lungs and lymphatic system, causing lung cysts, breathing problems, and sometimes chylous effusions.

The specialized endothelial cells lining lymphatic vessels.

A specialized gentle massage technique that promotes movement of lymph fluid to reduce swelling.

Included as part of the vascular system, it's a network of lymphatic vessels, lymph nodes, and organs (such as the spleen, thymus, and tonsils) that helps maintain fluid balance, filter harmful substances, and support immune function.

The vessels in the body that carry lymph.

Relating to or involving both lymphatic vessels and veins, often referring to connections or malformations that contain both vessel types.

microsurgical procedure that connects tiny, functional lymphatic vessels to nearby small veins, creating bypasses to drain excess lymph fluid, and reduce swelling.

Swelling caused by impaired lymphatic drainage, leading to fluid buildup in the skin and tissues. It may be primary (genetic) or secondary (due to surgery, cancer, or lymphatic anomalies).

A nuclear medicine imaging test that uses a small amount of radioactive tracer to evaluate lymphatic drainage and flow. It helps assess lymphatic function and detect blockages or leaks.

Lymphatic malformations with large, stretched vessels and cysts filled with lymph, blood from internal bleeding, or both.

A non-invasive imaging test that uses a strong magnet and radio waves to create detailed two- and three-dimensional images of the body, helping doctors diagnose and monitor disease.

Inflammation of the protective membranes (meninges) surrounding the brain and spinal cord, most often caused by infection. It can be life-threatening and requires urgent medical attention.

A type of dietary fat made from medium-chain triglycerides that is easier to digest and absorb than other fats and is often used to support nutrition in people with certain digestive or lymphatic conditions.

The central part of the chest between the lungs. It contains the heart, major blood vessels, trachea, esophagus, thymus, lymph nodes, and thoracic duct.

Targeted medications that block MEK proteins in the RAS/MAPK pathway. They are used in some conditions driven by that pathway.

A lymphatic malformation made up of very small cysts (typically smaller than 2 cm) that are diffuse and lack clear borders. Previously known as lymphangioma circumscriptum.

A lymphatic malformation that contains both large cysts (macrocystic) and small, diffuse cysts (microcystic).

A genetic condition in which a mutation is present in some cells of the body but not all. Mosaicism is common in lymphatic malformations and explains why symptoms may affect only certain body areas.

A gene involved in cell signaling and growth control. NRAS mutations can contribute to abnormal lymphatic development and vascular disorders.

When a medication is used to treat a condition other than the one it was officially approved for by the FDA.

A bone-forming cell responsible for producing new bone tissue.

A cell that breaks down old or damaged bone tissue as part of normal bone remodeling.

Cells found inside bone that develop from osteoblasts during bone formation. As new bone is laid down, some osteoblasts become trapped within it and mature into osteocytes.

The progressive condition of softening, absorption, and destruction of bony tissue. It is a function of the osteoclasts.

Bone condition characterized by bone density that is lower than normal. It is not as severe as in osteoporosis.

Condition that affects the bones, causing them to become weak and fragile and more likely to break (fracture).

Abnormal increase in the size of the body or a body part often caused by somatic or germline genetic variants.

A bone break that happens because the bone is weakened by an underlying medical condition.

Groups of interacting molecules inside a cell that work together to control specific functions, such as turning genes on or off or sending signals within the cell.

A thin, sac-like structure that surrounds the heart. It helps protect the heart, keeps it in place within the chest, and contains a small amount of fluid that allows the heart to move smoothly as it beats.

Accumulation of excess fluid in the pericardial space surrounding the heart. Severe cases may impair heart function.

A procedure in which an opening is made in the pericardium to drain fluid that has accumulated around the heart.

A surgical procedure that removes part or all of the pericardium, the sac that surrounds the heart. It is used to treat chronic inflammation or recurrent fluid buildup.

Medical procedure that uses a needle to remove fluid from the pericardial sac, the tissue that surrounds the heart.

Condition in which the sac-like covering around the heart (pericardium) becomes inflamed. It may cause chest pain, fever, or fluid buildup.

Lymphatic vessels located in the limbs, skin, and other peripheral tissues that collect lymph fluid and transport it toward central lymphatic structures.

A healthcare specialty that uses exercise, movement, and manual techniques to improve physical function, mobility, and quality of life in people with injuries or chronic conditions.

A gene involved in cell growth and survival. Mutations in PIK3CA can cause abnormal tissue overgrowth and are associated with lymphatic and vascular malformations, including PROS.

A thin double-layered membrane that surrounds each lung. The small amount of fluid between its layers allows smooth lung movement during breathing.

Excess fluid that builds up between the two pleural layers, the fluid-filled space that surrounds the lungs. Too much fluid can impair breathing by limiting the expansion of the lungs.

Surgical removal of part of the pleura, usually done to treat recurrent pneumothorax or pleural thickening.

A critical medical procedure designed to remove fluid or air from the pleural space, serving diagnostic and therapeutic purposes.

Procedure that adheres the outside of the lung to the inside of the chest cavity to prevent excess fluid collection in the space.

An infection of the lungs caused by bacteria, viruses, or fungi, leading to fever, cough, and difficulty breathing.

A condition in which air collects in the space between the lung and the chest wall, causing the lung to partially or fully collapse.

A group of disorders caused by somatic mutations in the PIK3CA gene, resulting in tissue overgrowth, vascular and lymphatic malformations, and asymmetry.

A condition where the body loses too much protein through the intestines. This can cause low blood protein levels and swelling.

A minimally invasive procedure that uses heat generated by radiofrequency energy to destroy or shrink targeted tissue. In lymphatic and vascular conditions, RFA may be used to treat abnormal vessels or lesions. It is different from radiofrequency neurotomy, which specifically targets nerves to relieve pain.

A treatment that uses high-energy radiation to destroy cancer cells or shrink tumors.

A group of genetic conditions caused by mutations in the RAS/MAPK signaling pathway, including Noonan syndrome, Costello syndrome, and cardio-facio-cutaneous (CFC) syndrome.

A medication injected during sclerotherapy that irritates the inside of a cyst or vessel, causing it to scar and shrink over time.

Medical procedure used to treat abnormal blood or lymphatic vessels, including vascular malformations. A medication is injected into the vessel or cyst, causing it to scar, shrink, or close over time. These procedures may require repeat treatments and are typically performed by interventional radiologists with lymphatic expertise.

The first lymph node (or group of nodes) that receives lymph drainage from a specific area of the body. It is often examined to assess how disease spreads through the lymphatic system.

A medication that affects the mTOR pathway (a growth and signaling pathway in cells). It is used in some people to help shrink or stabilize lymphatic and vascular malformations.

A somatic variant is a genetic change that happens after a baby begins to develop. It affects only some cells, is not inherited, and cannot be passed on to children.

Organ located above the stomach and under the ribs on the left side. Part of the lymphatic system, which fights infection and keeps your body fluids in balance, it contains white blood cells that fight germs. The spleen also helps control the amount of blood in the body, and destroys old and damaged cells.

Surgical removal of the spleen.

Enlargement of the spleen.

Bone in the center of the chest which attaches the ribs and protects the heart and lungs.

An operation to remove part or all of an LM. Complete removal is often difficult and the LM can reappear. It may be helpful for small or localized LMs, or to correct overgrowth.

An abnormal, fluid-filled cavity that forms within the spinal cord, which can expand over time and interfere with normal nerve function.

A treatment that blocks specific genes, proteins, or pathways involved in a disease, aiming to affect abnormal cells more than healthy cells.

Originating in the abdomen and traveling upward through the chest, the thoracic duct is the largest lymphatic vessel in the body and drains most of the body’s lymph into the bloodstream near the collarbone. In adults, it can transport about 4 liters of lymph fluid each day.

A surgical procedure in which the thoracic duct is tied off to stop the leakage of lymph. It is most often performed to treat chylothorax or persistent lymphatic leakage.

The part of the body between the neck and the diaphragm that contains the heart, lungs, major blood vessels, and other structures.

A method of providing all necessary nutrients directly into the bloodstream through an intravenous (IV) line when a person cannot eat or absorb nutrition through the digestive system.

A surgical procedure where a small opening is made in the front of the neck into the windpipe (trachea).

An imaging test that uses high-frequency sound waves to create pictures of internal organs and tissues. It is non-invasive and does not use radiation.

Affecting one side of the body.

A genetic change identified through testing whose impact on health is not yet known. Over time, a VUS may be reclassified as benign or disease-causing as more information becomes available.

The internal organs of the body, such as the lungs, heart, liver, stomach, intestines, and pancreas.

An imaging test that uses low doses of radiation to create pictures of structures inside the body, such as bones, lungs, and organs.