Vascular malformation is a collective term for different disorders of the vasculature (errors in vascular development). It can be a disorder of the capillaries, arteries, veins and lymphatic vessels or a disorder of a combination of these (lesions are named based on the primary vessel that is malformed). A vascular malformation consists of a cluster of deformed vessels, due to an error in vascular development (dysmorphogenesis). However, endothelial turnover is stable in these defects. Congenital vascular malformations are always already present at birth, although they are not always visible. In contrast to vascular tumors, vascular malformations do not have a growth phase, nor an involution phase. Vascular malformations tend to grow proportionately with the child. Vascular malformations never regress, but persist throughout life.

Vascular malformations can be divided into slow-flow, fast-flow and complex-combined types.

All fast-flow malformations are malformations involving arteries. They constitute about 14% of all vascular malformations.

- Arterial malformation

- Arteriovenous fistula (AVF) : a lesion with a direct communication via fistulae between an artery and a vein.

- Arteriovenous malformation : a lesion with a direct connection between an artery and a vein, without an intervening capillary bed, but with an interposed nidus of dysplastic vascular channels in between.

Cystic hygromas are increasingly diagnosed by prenatal ultrasonography. A common symptom is a neck growth. It may be found at birth, or discovered later in an infant after an upper respiratory tract infection. Cystic hygromas can grow very large and may affect breathing and swallowing. Some symptoms may include a mass or lump in the mouth, neck, cheek, or tongue. It feels like a large fluid-filled sac. In addition, cystic hygromas can be found in other body parts such as the arm, chest, legs, groin, and buttocks. Cystic hygromas are also often seen in Turner's syndrome, although a patient who does not have Turner's syndrome can present with this condition.

The birth defect is diagnosed by the presence of a combination of these symptoms (often on approximately ¼ of the body, though some cases may present more or less affected tissue):

- One or more distinctive port-wine stains with sharp borders

- Varicose veins

- Hypertrophy of bony and soft tissues, that may lead to local gigantism or shrinking, most typically in the lower body/legs.

- An improperly developed lymph system

In some cases, port-wine stains (capillary port wine type) may be absent. Such cases are very rare and may be classified as "atypical Klippel–Trenaunay syndrome".

KTS can either affect blood vessels, lymph vessels, or both. The condition most commonly presents with a mixture of the two. Those with venous involvement experience increased pain and complications, such as venous ulceration in the lower extremities.

Those with large AVMs are at risk of formation of blood clots in the vascular lesion, which may migrate to the lungs (pulmonary embolism). If there is large-volume blood flow through the lesion, "high-output heart failure" may develop due to the inability of the heart to generate sufficient cardiac output.

Microcystic lymphatic malformations are a cutaneous condition characterized by aggregations of ill-defined, abnormal, microscopic lymphatic channels.

A Cystic lymphatic malformation is a deep-seated, typically multilocular, ill-defined soft-tissue mass that is painless and covered by normal skin. These malformations may further be divided into macrocystic lymphatic malformations and microcystic lymphatic malformations.

There are three distinct types of lymphangioma, each with their own symptoms. They are distinguished by the depth and the size of abnormal lymph vessels, but all involve a malformation of the lymphic system. Lymphangioma circumscriptum can be found on the skin's surface, and the other two types of lymphangiomas occur deeper under the skin.

- Lymphangioma circumscriptum, a microcystic lymphatic malformation, resembles clusters of small blisters ranging in color from pink to dark red. They are benign and do not require medical treatment, although some patients may choose to have them surgically removed for cosmetic reasons.

- Cavernous lymphangiomas are generally present at birth, but may appear later in the child's life. These bulging masses occur deep under the skin, typically on the neck, tongue and lips, and vary widely in size, ranging from as small as a centimeter in diameter to several centimeters wide. In some cases, they may affect an entire extremity such as a hand or foot. Although they are usually painless, the patient may feel mild pain when pressure is exerted on the area. They come in the colors white, pink, red, blue, purple, and black; and the pain lessens the lighter the color of the bump.

- Cystic hygroma shares many commonalities with cavernous lymphangiomas, and some doctors consider them to be too similar to merit separate categories. However, cystic lymphangiomas usually have a softer consistency than cavernous lymphangiomas, and this term is typically the one that is applied to lymphangiomas that develop in fetuses. They usually appear on the neck (75%), arm pit or groin areas. They often look like swollen bulges underneath the skin.

Klippel–Trénaunay syndrome (KTS or KT), formerly Klippel–Trénaunay–Weber syndrome and sometimes angioosteohypertrophy syndrome and hemangiectatic hypertrophy, is a rare congenital medical condition in which blood vessels and/or lymph vessels fail to form properly. The three main features are nevus flammeus (port-wine stain), venous and lymphatic malformations, and soft-tissue hypertrophy of the affected limb. It is similar to, though distinctly separate from, the less common Parkes-Weber syndrome.

The classical triad of Klippel-Trenaunay syndrome consists of:

1. vascular malformations of the capillary, venous and lymphatic vessels;

2. varicosities of unusual distribution, particularly the lateral venous anomaly; and

3. unilateral soft and skeletal tissue hypertrophy, usually the lower extremity.

A cystic hygroma, also known as cystic lymphangioma and macrocystic lymphatic malformation, is an often congenital multiloculated lymphatic lesion that can arise anywhere, but is classically found in the left posterior triangle of the neck and armpits. This is the most common form of lymphangioma. It contains large cyst-like cavities containing lymph, a watery fluid that circulates throughout the lymphatic system. Microscopically, cystic hygroma consists of multiple locules filled with lymph. In the depth, the locules are quite big but they decrease in size towards the surface.

Cystic hygromas are benign, but can be disfiguring. It is a condition which usually affects children; very rarely it can present in adulthood.

Cystic hygroma is also known as lymphatic malformation. Currently, the medical field prefers to use the term lymphatic malformation because the term cystic hygroma means water tumor. Lymphatic malformation is more commonly used now because it is a sponge-like collection of abnormal growth that contains clear lymphatic fluid. The fluid collects within the cysts or channels, usually in the soft tissue. Cystic hygromas occur when the lymphatic vessels that make up the lymphatic system are not formed properly. There are two types of lymphatic malformations. They are macrocystic lymphatic malformations, large cysts, and microcystic, small cysts. A person may have only one kind of the malformation or can have a mixture of both macro and micro cysts.

Cystic hygroma can be associated with a nuchal lymphangioma or a fetal hydrops. Additionally, it can be associated with Turner syndrome or with Noonan syndrome.

A lethal version of this condition is known as Cowchock Wapner Kurtz syndrome that, in addition to cystic hygroma, includes cleft palate and lymphedema, a condition of localized edema and tissue swelling caused by a compromised lymphatic system.

Lymphangiomatosis has been reported in every region of the abdomen, though the most reported sites involve the intestines and peritoneum; spleen, kidneys, and liver. Often there are no symptoms until late in the progression of the disease. When they do occur, symptoms include abdominal pain and/or distension; nausea, vomiting, diarrhea; decreased appetite and malnourishment. When the disease affects the kidneys the symptoms include flank pain, abdominal distension, blood in the urine, and, possibly, elevated blood pressure, which may result in it being confused with other cystic renal disease. When lymphangiomatosis occurs in the liver and/or spleen it may be confused with polycystic liver disease. Symptoms may include abdominal fullness and distension; anemia, disseminated intravascular coagulopathy (DIC), fluid accumulation in the abdomen(ascites), decreased appetite, weight loss, fatigue; late findings include liver failure.

Lymphangiomas are malformations of the lymphatic system characterized by lesions that are thin-walled cysts; these cysts can be macroscopic, as in a cystic hygroma, or microscopic. The lymphatic system is the network of vessels responsible for returning to the venous system excess fluid from tissues as well as the lymph nodes that filter this fluid for signs of pathogens. These malformations can occur at any age and may involve any part of the body, but 90% occur in children less than 2 years of age and involve the head and neck. These malformations are either congenital or acquired. Congenital lymphangiomas are often associated with chromosomal abnormalities such as Turner syndrome, although they can also exist in isolation. Lymphangiomas are commonly diagnosed before birth using fetal ultrasonography. Acquired lymphangiomas may result from trauma, inflammation, or lymphatic obstruction.

Most lymphangiomas are benign lesions that result only in a soft, slow-growing, "doughy" mass. Since they have no chance of becoming malignant, lymphangiomas are usually treated for cosmetic reasons only. Rarely, impingement upon critical organs may result in complications, such as respiratory distress when a lymphangioma compresses the airway. Treatment includes aspiration, surgical excision, laser and radiofrequency ablation, and sclerotherapy.

Lymphangiomatosis is a multi-system disorder. Symptoms depend on the organ system involved and, to varying degrees, the extent of the disease. Early in the course of the disease patients are usually asymptomatic, but over time the abnormally proliferating lymphatic channels that constitute lymphangiomatosis are capable of massive expansion and infiltration into surrounding tissues, bone, and organs. Because of its slow course and often vague symptoms, the condition is frequently under-recognized or misdiagnosed.

Early signs of disease in the chest include wheezing, cough, and feeling short of breath, which is often misdiagnosed as asthma. The pain that accompanies bone involvement may be attributed to "growing pains" in younger children. With bone involvement the first indication for disease may be a pathological fracture. Symptoms may not raise concern, or even be noted, until the disease process has advanced to a point where it causes restrictive compression of vital structures. Further, the occurrence of chylous effusions seems to be unrelated to the pathologic "burden" of the disease, the extent of involvement in any particular tissue or organ, or the age of the patient. This offers one explanation as to why, unfortunately, the appearance of chylous effusions in the chest or abdomen may be the first evidence of the disease.

Following are some of the commonly reported symptoms of lymphangiomatosis, divided into the regions/systems in which the disease occurs:

Chronic diarrhea is almost always seen with lymphangiectasia, but most other signs are linked to low blood protein levels (hypoproteinemia), which causes low oncotic pressure. These signs include ascites, pleural effusion, and edema of the limbs and trunk. Weight loss is seen with long-term disease.

The clinical manifestation and presentation of symptoms of lymphedema develop following a significant degree of injury. Secondary lymphedema is the lymphadenectomy and lymphatic injury following surgery, radiation, chemotherapy, and/or trauma which healing or regeneration of damaged lymphatics may occur with variable success.

Symptoms will include swelling, edema, and pain from a multitude of secondary complications (pressure, musculoskeletal disorder from asymmetry, restricted blood flow). Most patients will avoid discussing pain for many reasons, so this will require logical thinking or communication skills to assess. In advanced lymphedema, there may be the presence of skin changes such as discoloration, verrucous (wart-like) hyperplasia, hyperkeratosis, papillomatosis, and Ulcer (dermatology).

Lymphedema should not be confused with edema arising from venous insufficiency, which is not lymphedema. In addition to a compressive local environment of lymphedematous extremity, long standing venous compression potentially contributed to an increased propensity for thrombosis due to vascular changes from longstanding venous hypertension from a proximal compression or simply from a change in blood flow. However, untreated venous insufficiency can progress into a combined venous/lymphatic disorder. Proper imaging can help identify where the dysfunction is in the system, and is essential in identifying the source before treatment is decided.

Presented here is an extreme case of severe unilateral hereditary lymphedema which had been present for 25 years without treatment:

Superficial lymphatic malformation (also known as "Lymphangioma circumscriptum") is a congenital malformation of the superficial lymphatics, presenting as groups of deep-seated, vesicle-like papules resembling frog spawn, at birth or shortly thereafter.

Lymphohemangioma, or lymphohaemangioma, () is a disease characterized by swelling of the lymph nodes and blood vessels. It is variously described as a "mixture of clear fluid and blood-filled cysts", a mass of abnormal swollen veins and lymph nodes, or a tumorous growth of lymph and blood vessels. It is also sometimes described as a misnomer for combined lymphatic and capillary malformation.

Lymphohemangioma commonly appears in and around the eyes and mouth, but may also occur in other areas, including the pelvis, urethra, bladder, and in the limbs. Amputation of extremities may be necessary if the disease renders the extremity non-functional.

Lymphedema affects approximately 140 million people worldwide.

Lymphedema may be inherited (primary) or caused by injury to the lymphatic vessels (secondary). It is most frequently seen after lymph node dissection, surgery and/or radiation therapy, in which damage to the lymphatic system is caused during the treatment of cancer, most notably breast cancer. In many patients with cancer, this condition does not develop until months or even years after therapy has concluded. Lymphedema may also be associated with accidents or certain diseases or problems that may inhibit the lymphatic system from functioning properly. In tropical areas of the world, a common cause of secondary lymphedema is filariasis, a parasitic infection. It can also be caused by a compromising of the lymphatic system resulting from cellulitis.

While the exact cause of primary lymphedema is still unknown, it generally occurs due to poorly developed or missing lymph nodes and/or channels in the body. Lymphedema may be present at birth, develop at the onset of puberty (praecox), or not become apparent for many years into adulthood (tarda). In men, lower-limb primary lymphedema is most common, occurring in one or both legs. Some cases of lymphedema may be associated with other vascular abnormalities.

Secondary lymphedema affects both men and women. In women, it is most prevalent in the upper limbs after breast cancer surgery, in particular after axillary lymph node dissection, occurring in the arm on the side of the body in which the surgery is performed. Breast and trunk lymphedema can also occur but, go unrecognised as there is swelling in the area after surgery and its symptoms ( peau d' orange and/or an inverted nipple ) can be confused with post surgery fat necrosis. In Western countries, secondary lymphedema is most commonly due to cancer treatment. Between 38 and 89% of breast cancer patients suffer from lymphedema due to axillary lymph node dissection and/or radiation. Unilateral lymphedema occurs in up to 41% of patients after gynecologic cancer. For men, a 5-66% incidence of lymphedema has been reported in patients treated with incidence depending on whether staging or radical removal of lymph glands was done in addition to radiotherapy.

Head and neck lymphedema can be caused by surgery or radiation therapy for tongue or throat cancer. It may also occur in the lower limbs or groin after surgery for colon, ovarian or uterine cancer, in which removal of lymph nodes or radiation therapy is required. Surgery or treatment for prostate, colon and testicular cancers may result in secondary lymphedema, particularly when lymph nodes have been removed or damaged.

The onset of secondary lymphedema in patients who have had cancer surgery has also been linked to aircraft flight (likely due to decreased cabin pressure or relative immobility). For cancer survivors, therefore, wearing a prescribed and properly fitted compression garment may help decrease swelling during air travel.

Some cases of lower-limb lymphedema have been associated with the use of tamoxifen, due to the blood clots and deep vein thrombosis (DVT) that can be caused by this medication. Resolution of the blood clots or DVT is needed before lymphedema treatment can be initiated.

Lymphangiectasia is a pathologic dilation of lymph vessels. When it occurs in the intestines of dogs, and more rarely humans, it causes a disease known as "intestinal lymphangiectasia." This disease is characterized by lymphatic vessel dilation, chronic diarrhea and loss of proteins such as serum albumin and globulin. It is considered to be a chronic form of protein-losing enteropathy.

It is also known as "lymphangiectasis".

The most common presentation of Milroy Disease is bilateral lower extremity lymphedema, and may also be accompanied by hydrocele.

Angiomas are benign tumors derived from cells of the vascular or lymphatic vessel walls (endothelium) derived from cells of the tissues surrounding these vessels.

Angiomas are a frequent occurrence as patients age, but they might be an indicator of systemic problems such as liver disease. They are not commonly associated with malignancy.

Angiomas usually appear at or near the surface of the skin anywhere on the body, and may be considered bothersome depending on their location. However, they may be present as symptoms of another more serious disorder, such as cirrhosis. When they are removed, it is generally for cosmetic reasons.

A lymphocele is a collection of lymphatic fluid within the body not bordered by epithelial lining. It is usually a surgical complication seen after extensive pelvic surgery (such as cancer surgery) and is most commonly found in the retroperitoneal space. Spontaneous development is rare.

Milroy's disease (MD) is a familial disease characterized by lymphedema, commonly in the legs, caused by congenital abnormalities in the lymphatic system. Disruption of the normal drainage of lymph leads to fluid accumulation and hypertrophy of soft tissues. It is also known as Milroy disease, Nonne-Milroy-Meige syndrome and hereditary lymphedema.

It was named by Sir William Osler for William Milroy, a Canadian physician, who described a case in 1892, though it was first described by Rudolf Virchow in 1863.

Many lymphoceles are asymptomatic. Larger lymphoceles may cause symptoms related to compression of adjacent structures leading to lower abdominal pain, abdominal fullness, constipation, urinary frequency, and edema of the genitals and/or legs. Serious sequelae could develop and include infection of the lymphocele, obstruction and infection of the urinary tract, intestinal obstruction, venous thrombosis, pulmonary embolism, chylous ascites and lymphatic fistula formation.

On clinical examination the skin may be reddened and swollen and a mass felt. Ultrasonography or CT scan will help to establish a diagnosis.

Other fluid collections to be considered in the differential diagnosis are urinoma, seroma, hematoma, as well as collections of pus. Also, when lower limb edema is present, venous thrombosis needs to be considered.

Macrocheilia is a condition of permanent swelling of the lip that results from greatly distended lymphatic spaces. This causes an abnormal largeness of the lips. This is sometimes seen in leprosy patients.