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.

a combination of various vascular malformations. They are 'complex' because they involve a combination of two different types of vessels.

- CVM: capillary venous malformation

- CLM: capillary lymphatic malformation

- LVM: lymphatic venous malformation

- CLVM: capillary lymphatic venous malformation. CLVM is associated with Klippel-Trenaunay syndrome

- AVM-LM: Arteriovenous malformation- lymphatic malformation

- CM-AVM: capillary malformation- arteriovenous malformation

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 blockage of cerebrospinal fluid (CSF) flow may also cause a syrinx to form, eventually leading to syringomyelia. Central cord symptoms such as hand weakness, dissociated sensory loss, and, in severe cases, paralysis may occur.

Syringomyelia is a chronic progressive degenerative disorder characterized by a fluid-filled cyst located in the spinal cord. Its symptoms include pain, weakness, numbness, and stiffness in the back, shoulders, arms or legs. Other symptoms include headaches, the inability to feel changes in the temperature, sweating, sexual dysfunction, and loss of bowel and bladder control. It is usually seen in the cervical region but can extend into the medulla oblongata and pons or it can reach downward into the thoracic or lumbar segments. Syringomyelia is often associated with Chiari malformation type I and is commonly seen between the C-4 and C-6 levels. The exact development of syringomyelia is unknown but many theories suggest that the herniated tonsils in Chiari malformation type I form a "plug" which does not allow an outlet of CSF from the brain to the spinal canal. Syringomyelia is present in 25% of patients with Chiari malformation.

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.

The key features of this syndrome are an enlargement of the fourth ventricle; complete absence of the cerebellar vermis, the posterior midline area of cerebellar cortex responsible for coordination of the axial musculature; and cyst formation near the internal base of the skull. An increase in the size of the fluid spaces surrounding the brain as well as an increase in pressure may also be present. The syndrome can appear dramatically or develop unnoticed.

Symptoms, which often occur in early infancy, include slower motor development and progressive enlargement of the skull. In older children, symptoms of increased intracranial pressure such as irritability, vomiting, and convulsions and signs of cerebellar dysfunction such as unsteadiness and lack of muscle coordination or jerky movements of the eyes may occur. Other symptoms include increased head circumference, bulging at the back of the skull, problems with the nerves that control the eyes, face and neck, and abnormal breathing patterns.

Dandy–Walker syndrome is frequently associated with disorders of other areas of the central nervous system including absence of the corpus callosum, the bundle of axons connecting the two cerebral hemispheres, and malformations of the heart, face, limbs, fingers and toes.

The Dandy–Walker complex is a genetically sporadic disorder that occurs one in every 30,000 live births. Prenatal diagnosis and prognosis of outcomes associated with Dandy–Walker can be difficult. Prenatal diagnosis is possible with ultrasound. Because the syndrome is associated with an increased risk for fetal karyotype abnormalities, amniocentesis can be offered after prenatal diagnosis. There is a relative contraindication of taking Warfarin during pregnancy, as it is associated with an increased risk of Dandy–Walker syndrome if taken during the first trimester.

The DWS malformation is the most severe presentation of the syndrome. The posterior fossa is enlarged and the tentorium is in high position. There is complete agenesis of the cerebellar vermis. There is also cystic dilation of the fourth ventricle, which fills the posterior fossa. This often involves hydrocephalus and complications due to associated genetic conditions, such as Spina Bifida.

Macrocephaly-capillary malformation (M-CM) is a multiple malformation syndrome causing abnormal body and head overgrowth and cutaneous, vascular, neurologic, and limb abnormalities. Though not every patient has all features, commonly found signs include macrocephaly, congenital macrosomia, extensive cutaneous capillary malformation (naevus flammeus or port-wine stain type birthmark over much of the body; a capillary malformation of the upper lip or philtrum is seen in many patients with this condition), body asymmetry (also called hemihyperplasia or hemihypertrophy), polydactyly or syndactyly of the hands and feet, lax joints, doughy skin, variable developmental delay and other neurologic problems such as seizures and low muscle tone.

The diagnosis of constriction ring syndrome can be confirmed with an ultrasonography. The clinical manifestations can be extremely variable. It could be a single or multiple manifestation. This can be confirmed at the end of the first trimester or at the beginning of the second trimester. But not every patient will be diagnosed at that moment, most will get this diagnosis at birth.

It involves numerous anomalies including:

- Post-axial polydactyly

- Congenital heart defects (most commonly an atrial septal defect producing a common atrium, occurring in 60% of affected individuals)

- Teeth present at birth (natal teeth)

- Fingernail dysplasia

- Short-limbed dwarfism, mesomelic pattern

- Short ribs

- Cleft palate

- Malformation of the wrist bones (fusion of the hamate and capitate bones).

Aphalangy, hemivertebrae and urogenital-intestinal dysgenesis is an extremely rare syndrome, described only in three siblings. It associates hypoplasia or aplasia of phalanges of hands and feet, hemivertebrae and various urogenital and/or intestinal abnormalities. Intrafamilial variability is important as one sister had lethal abnormalities (Potter sequence and pulmonary hypoplasia), while her affected brother was in good health with normal psychomotor development at 6 months of age. Prognosis seems to depend mainly on the severity of visceral malformations. Etiology and inheritance remain unknown.

Constriction ring syndrome (CRS) is a congenital disorder with unknown cause. Because of the unknown cause there are many different, and sometimes wrong names. It is a malformation due to intrauterine bands or rings that give deep grooves in, most commonly, distal extremities like fingers and toes. In rare cases the constriction ring can form around other parts of the fetus and cause amputation or even intrauterine death (see Types and Classification). The anatomy proximal to the site of constriction (or amputation) is developmentally normal.

CRS can be associated with other malformations with club foot being most common.

(see also Types and Classification).

The precise configuration of the bands, lymphedema, and character of the amputations are not predictable and vary with each individual patient. Also more than one extremity is usually affected, and it is rare for only one ring to present as an isolated malformation with no other manifestation of this syndrome.

Sinus pericranii typically present as soft palpable masses along midline skull, which may fluctuate in size depending on body positioning. Classically, these lesions are not associated with color change of the overlying skin, such as with other vascular lesions such as hemangioma.

Diagnosis is usually based on clinical observation. Various sets of criteria have been suggested to identify the disorder in an individual patient, all of which include macrocephaly and a number of the following: somatic overgrowth, cutis marmorata, midline facial birthmark, polydactyly/syndactyly, asymmetry (hemihyperplasia or hemihypertrophy), hypotonia at birth, developmental delay, connective tissue defect and frontal bossing. Currently no consensus exists about which diagnostic criteria are definitive and so evaluation by a medical geneticist or other clinician with familiarity with the syndrome is usually needed to provide diagnostic certainty. It is not clear if there are some features which are mandatory to make the diagnosis, but macrocephaly appears essentially universal though may not be congenital. The distinctive vascular abnormalities of the skin often fade over time, making the diagnosis challenging in older children with this condition.

The brain can be affected in several ways in this syndrome. Some children are born with structural brain anomalies such as cortical dysplasia or polymicrogyria. While developmental delay is nearly universal in this syndrome it is variable in severity, with the majority having mild to moderate delays and a minority having severe cognitive impairment. Some patients are affected with a seizure disorder. White matter abnormalities on magnetic resonance imaging (MRI), suggesting a delay in white matter myelination, is commonly seen in early childhood. Some patients may have asymmetry of the brain, with one side being noticeably larger than the other.

One interesting phenomenon that seems very common in this syndrome is the tendency for disproportionate brain growth in the first few years of life, with crossing of percentiles on the head circumference growth charts. A consequence of this disproportionate brain growth appears to be a significantly increased risk of cerebellar tonsillar herniation (descent of the cerebellar tonsils through the foramen magnum of the skull, resembling a Chiari I malformation neuroradiologically) and ventriculomegaly/hydrocephalus. Such cerebellar tonsil herniation may occur in up to 70% of children with M-CM.

The medical literature suggests that there is a risk of cardiac arrhythmias in early childhood. The cause for this is unknown. In addition, a variety of different congenital cardiac malformations have been reported in a small number of patients with this disorder.

Like other syndromes associated with disproportionate growth, there appears to be a slightly increased risk of certain types of childhood malignancies in M-CM (such as Wilms' tumor). However, the precise incidence of these malignancies is unclear.

Infantile myofibromatosis (also known as "Congenital generalized fibromatosis," and "Congenital multicentric fibromatosis") is the most common fibrous tumor of infancy, in which eighty percent of patients have solitary lesions with half of these occurring on the head and neck, and 60% are present at or soon after birth. Less commonly, infantile myofibromatosis presents as multiple lesions of skin, muscle, and bone with about 1/3 of these cases also having lesions in their visceral organs. All of these cases have an excellent prognosis with their tumors sometimes regressing spontaneously except for those cases in which there is visceral involvement where the prognosis is poor. Infantile myofibromatosis and the classic form of mesoblastic nephroma have been suggested to be the same disease because of their very similar histology. However, studies on the distribution of cell-type markers (i.e. cyclin D1 and Beta-catenin) indicate that the two neoplasms likely have different cellular origins.

Benign neonatal hemangiomatosis is a cutaneous condition in infants, characterized by multiple cutaneous lesions without evident visceral hemangiomas.

Venous malformation is a subtype of vascular malformation affecting the venous vasculature. They are usually congenital and found at birth and are treated by Schlerotherapy or Laser Therapy.

Ocular disc dysplasia is the most notable ocular defect of the disease. An abnormal development in the optic stalk causes optic disc dysplasia, which is caused by a mutation in the "Pax2" gene. The nerve head typically resembles the morning glory disc anomaly, but has also been described as a coloboma. A coloboma is the failure to close the choroid fissure, which is the opening from the ventral side of the retina in the optic stalk. Despite the similarities with coloboma and morning glory anomaly, significant differences exist such that optic disc dysplasia cannot be classified as either one entity.

Optic disc dysplasia is noted by an ill-defined inferior excavation, convoluted origin of the superior retinal vessels, excessive number of vessels, infrapapillary pigmentary disturbance, and slight band of retinal elevation adjacent to the disk. Some patients have normal or near normal vision, but others have visual impairment associated with the disease, though it is not certain if this is due only to the dysplastic optic nerves, or a possible contribution from macular and retinal malformations. The retinal vessels are abnormal or absent, in some cases having small vessels exiting the periphery of the disc. There is a great deal of clinical variability.

The most common malformation in patients with the syndrome is kidney hypodysplasia, which are small and underdeveloped kidneys, often leading to end-stage renal disease (ESRD). Estimates show approximately 10% of children with hypoplastic kidneys are linked to the disease. Many different histological abnormalities have been noted, including:

- decrease in nephron number associated with hypertrophy

- focal segmental glomerulosclerosis

- interstitial fibrosis and tubular atrophy

- multicystic dysplastic kidney

Up to one-third of diagnosed patients develop end stage kidney disease, which may lead to complete kidney failure.

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.

Sinus pericranii (SP) is a rare disorder characterized by a congenital (or occasionally, acquired) epicranial venous malformation of the scalp. Sinus pericranii is an abnormal communication between the intracranial and extracranial venous drainage pathways. Treatment of this condition has mainly been recommended for aesthetic reasons and prevention of hemorrhage.

Vascular malformation is a blood vessel abnormality. There are many types, but the most common is arteriovenous malformation.

It may cause aesthetic problems as it has a growth cycle and can continue to grow throughout life. This is also known as Vascular giantism or lymphangiomas.

Cavernous hemangiomas are the most common benign tumors of the liver. Usually one tumor exists, but multiple lesions can occur in the left or right lobe of the liver in 40% of patients. Their sizes can range from a few millimeters to 20 centimetres. Those over 5 cm are often referred to as "giant hemangiomas".

Cavernous hemangioma, also called cavernous angioma, cavernoma, or cerebral cavernous malformation (CCM) (when referring to presence in the brain) is a type of blood vessel malformation or hemangioma, where a collection of dilated blood vessels form a benign tumor. Because of this malformation, blood flow through the cavities, or caverns, is slow. Additionally, the cells that form the vessels do not form the necessary junctions with surrounding cells. Also, the structural support from the smooth muscle is hindered, causing leakage into the surrounding tissue. It is the leakage of blood, known as a hemorrhage from these vessels that causes a variety of symptoms known to be associated with this disease.