Diagnosis is generally made by magnetic resonance imaging (MRI), particularly using a specific imaging technique known as a gradient-echo sequence MRI, which can unmask small or punctate lesions that may otherwise remain undetected. These lesions are also more conspicuous on FLAIR imaging compared to standard T2 weighing. FLAIR imaging is different from gradient sequences. Rather, it is similar to T2 weighing but suppresses free-flowing fluid signal. Sometimes quiescent CCMs can be revealed as incidental findings during MRI exams ordered for other reasons. Many cavernous hemangiomas are detected "accidentally" during MRIs searching for other pathologies. These "incidentalomas" are generally asymptomatic. In the case of hemorrhage, however, a CT scan is more efficient at showing new blood than an MRI, and when brain hemorrhage is suspected, a CT scan may be ordered first, followed by an MRI to confirm the type of lesion that has bled.

Sometimes the lesion appearance imaged by MRI remains inconclusive. Consequently neurosurgeons will order a cerebral angiogram or magnetic resonance angiogram (MRA). Since CCMs are low flow lesions (they are hooked into the venous side of the circulatory system), they will be angiographically occult (invisible). If a lesion is discernible via angiogram in the same location as in the MRI, then an arteriovenous malformation (AVM) becomes the primary concern.

There is disagreement as to how cases of KTS should be classified if there is an arteriovenous fistula present. Although several authorities have suggested that the term Parkes-Weber syndrome is applied in those cases, ICD-10 currently uses the term "Klippel–Trénaunay–Weber syndrome".

Congenital hemangioma can be distinguished from infantile hemangioma because it is fully developed at birth. It forms during prenatal life and has reached its maximal size at birth. Congenital hemangioma can even be diagnosed in utero by prenatal ultrasound. Unlike IH, CH is more common in the extremities, has an equal sex distribution, and is solitary, with an average diameter of 5 cm. It commonly presents in the head and neck and in the lower extremities.

Congenital hemangioma are divided into 2 subgroups: the rapidly involuting congenital hemangiomas (RICHs) and the non-involuting congenital hemangiomas(NICHs).

The rapidly involuting congenital hemangioma, RICH, presents at birth as a solitary raised tumor with a central depression, scar, or ulceration surrounded by a rim of pallor. It is noted for its involution, which typically begins several weeks after birth and is completed no later than 14 months of age. After regression RICH may cause a residual deformity, such as atrophic skin and subcutaneous tissue. It mainly affects the limbs (52%), but also the head and neck region (42%) and the trunk (6%).

The non-involuting congenital hemangioma, NICH, presents as a solitary, well-circumscribed reddish-pink to purple plaque with central telangiectasia and hypopigmented rim. In contrast to RICH, NICH does not involute and rarely ulcerates. It persists into late childhood and can even mimic a vascular malformation by growing commensurately with the child. Although NICH can resemble RICH in its external appearance, it can be differentiated from RICH by a greater elevation and coarse telangiectases. It mainly affects the head and neck region (43%), but also the limbs (38%) and the trunk (19%).

Surgical resection for congenital hemangiomas is rarely needed, because RICH undergoes postnatal regression and NICH is benign and often asymptomatic. Resection may be indicated to improve the appearance of the affected area, as long as the surgical scar is less noticeable than the lesion. Other indications are problematic ulcers with persistent bleeding or chronic infection.

Although most NICH lesions are non-problematic and do not cause significant deformity, the threshold for resection of NICH is lower, because it neither involutes, nor responds to pharmacotherapy. RICH tumors are observed until involution is completed. Involuted RICH may leave behind atrophic tissue, which can be reconstructed with autologous grafts. It is often best to postpone excision until regression is complete.

There are effective pharmacologic treatments, which include intralesional corticosteroid injection, systemic corticosteroid injection, interferon α-2a or α-2b and angiogenic inhibitors. The use of corticosteroids leads to accelerated regression in 30%, stabilization of growth in 40%, lightening of color and softening of the tumor. However, 30% shows minimal or no response. Another drug treatment is interferon α-2a or α-2b. It is often used for patients who did not respond to corticosteroids. Although the response rate is much slower, it has been successful for 80% of children treated. The most serious side effect of interferon is a spastic diplegia. Other therapeutic options are embolization and pulsed-dye laser, which improves residual telangiectasias in RICH and in NICH.

Kaposiform hemangioendothelioma (KHE) is a rare vascular neoplasm that is locally aggressive but without metastatic potential. It occurs particularly in the skin, deep soft tissue, retroperitoneum, mediastinum, and rarely in bone. Although lesions occur solitary, they often involve large areas of the body, such as the head/neck region (40%), trunk (30%), or extremity (30%).

Usually, it is present at birth as a flat, reddish-purple, tense and edematous lesion.

Although half of lesions are congenital, 58% of KHE develop during infancy, 32% between age 1 and 10 years (32%) and 10% after 11 years of age. Moreover, adult onset has been described too with mainly males being affected. Both sexes are affected equally in children.

Lesions are often greater than 5 cm in diameter and can cause visible deformity and pain. During early childhood, KHE may enlarge and after 2 years of age, it may partially regress. Though, it usually persists longterm. In addition, 50% of patients suffer from coagulopathy due to thrombocytopenia (<25,000/mm3), presenting with petechiae and bleeding. This is called the Kasabach-Merritt Phenomenon, which is caused by trapping of platelets and other clotting factors within the tumor. Kasabach-Merritt Phenomenon is less likely in patients with lesions less than 8 cm. As two-thirds of adult-onset KHE tumors are less than 2 cm, KHE in adults is rarely associated with Kasabach-Merritt Phenomenon.

Patients with KHE and Kasabach-Merritt Phenomenon present with petechiae and ecchymosis.

Most KHE tumors are diffuse involving multiple tissue planes and important structures. Resection of KHE is thus often difficult. Treatment of kaposiform hemangioendothelioma is therefore medical. The primary drug is interferon alfa, which is successful in 50% of children. Another option is vincristine, which has lots of side-effects, but has a response rate of 90%. Drug therapy is often used in shrinking the tumor and treating the coagulopathy. However, many of these kaposiform hemangioendotheliomas do not completely regress and remain as a much smaller asymptomatic tumor. However, KHE still has a high mortality rate of 30%. Although complete surgical removal with a large margin has the best reported outcome, it is usually not done because of the risk of bleeding, extensiveness, and the anatomic site of the lesion.

Operative management may be possible for small or localized lesions. Removal of larger areas also may be indicated for symptomatic patients or for patients who have failed farmacotherapy. Resection is not required for lesions that are not causing functional problems, because KHE is benign and because resection could cause deformity.

A healthcare provider can usually diagnose a port-wine stain based entirely upon the history and appearance. In unusual cases, a skin biopsy may be needed to confirm the diagnosis. Depending on the location of the birthmark and other associated symptoms, a physician may choose to order a measurement of intraocular pressure or X-ray of the skull.

A MRI scan of the brain may be performed (under anesthesia) on infants who have a port-wine stain in the head area in order to check for signs of Sturge-Weber syndrome.

If the port-wine stain is inside the mouth, a provider may check the insides of a newborn baby's throat with a scope to see if there are any changes (growths) other than just the color.

If the port-wine stain is around the eye or on the eyelid, a referral may be made to an optometrist or ophthalmologist for a test of the ocular pressures in that eye. If swelling occurs in the port-wine stain, it may cause vision problems, glaucoma, or blindness.

KTS is a complex syndrome, and no single treatment is applicable for everyone. Treatment is decided on a case-by-case basis with the individual's doctors.

At present, many of the symptoms may be treated, but there is no cure for Klippel–Trenaunay syndrome.

Treatment depends on the anatomy of the malformation as determined by angiography or Magnetic Resonance Imaging (MRI).

In the absence of successful treatment, hypertrophy (increased tissue mass) of the stains may cause problems later in life, such as loss of function (especially if the stain is near the eye or mouth), bleeding, and increasing disfigurement. Lesions on or near the eyelid can be associated with glaucoma. If the port-wine stain is on the face or other highly visible part of the body, its presence can also cause emotional and social problems for the affected person.

It is suggested that gene therapy might be used as a cure in the future.

The incidence in the general population is roughly 0.5%, and clinical symptoms typically appear between 20 to 30 years of age. Once thought to be strictly congenital, these vascular lesions have been found to occur "de novo". It may appear either sporadically or exhibit autosomal dominant inheritance.

Oral propranolol appears to be the most effective treatment for reducing the size of capillary hemangiomas in children and is more effective than placebo, observation without intervention, or oral corticosteroids.

The surgical treatment involves the resection of the extracranial venous package and ligation of the emissary communicating vein. In some cases of SP, surgical excision is performed for cosmetic reasons. The endovascular technique has been described by transvenous approach combined with direct puncture and the recently endovascular embolization with Onyx.

Testing for a malformed vein of Galen is indicated when a patient has heart failure which has no obvious cause. Diagnosis is generally achieved by signs such as cranial bruits and symptoms such as expanded facial veins. The vein of Galen can be visualized using ultrasound or Doppler. A malformed Great Cerebral Vein will be noticeably enlarged. Ultrasound is a particularly useful tool for vein of Galen malformations because so many cases occur in infancy and ultrasound can make diagnoses prenatally. Many cases are diagnosed only during autopsy as congestive heart failure occurs very early.

AVMs are diagnosed primarily by the following methods:

- Computerized tomography (CT) scan is a noninvasive X-ray to view the anatomical structures within the brain to detect blood in or around the brain. A newer technology called CT angiography involves the injection of contrast into the blood stream to view the arteries of the brain. This type of test provides the best pictures of blood vessels through angiography and soft tissues through CT.

- Magnetic resonance imaging (MRI) scan is a noninvasive test, which uses a magnetic field and radio-frequency waves to give a detailed view of the soft tissues of the brain.

- Magnetic resonance angiography (MRA) – scans created using magnetic resonance imaging to specifically image the blood vessels and structures of the brain. A magnetic resonance angiogram can be an invasive procedure, involving the introduction of contrast dyes (e.g., gadolinium MR contrast agents) into the vasculature of a patient using a catheter inserted into an artery and passed through the blood vessels to the brain. Once the catheter is in place, the contrast dye is injected into the bloodstream and the MR images are taken. Additionally or alternatively, flow-dependent or other contrast-free magnetic resonance imaging techniques can be used to determine the location and other properties of the vasculature.

AVMs can occur in various parts of the body:

- brain (cerebral AV malformation)

- spleen

- lung

- kidney

- spinal cord

- liver

- intercostal space

- iris

- spermatic cord

- extremities – arm, shoulder, etc.

AVMs may occur in isolation or as a part of another disease (for example, Von Hippel-Lindau disease or hereditary hemorrhagic telangiectasia).

AVMs have been shown to be associated with aortic stenosis.

Bleeding from an AVM can be relatively mild or devastating. It can cause severe and less often fatal strokes. If a cerebral AVM is detected before a stroke occurs, usually the arteries feeding blood into the nidus can be closed off to avert the danger. However, interventional therapy may also be relatively risky.

A capillary hemangioma (also known as an Infantile hemangioma, Strawberry hemangioma, and Strawberry nevus) is the most common variant of hemangioma which appears as a raised, red, lumpy area of flesh anywhere on the body, though 83% occur on the head or neck area. These marks occur in about 10% of all births, and usually appear between one and four weeks after birth. It may grow rapidly, before stopping and slowly fading. Some are gone by the age of 2, about 60% by 5 years, and 90–95% by 9 years. Capillary hemangioma is a vascular anomaly.

Capillary hemangiomas occur 5 times more often in female infants than in males, and mostly in Caucasian populations. Additionally, low birthweight infants have a 26% chance of developing a hemangioma.

It is the most common tumor of orbit and periorbital areas in childhood. It may occur in the skin, subcutaneous tissues and mucous membranes of oral cavities and lips as well as in the liver, spleen and kidneys. While this birthmark may be alarming in appearance, physicians generally counsel that it be left to disappear on its own, unless it is in the way of vision or blocking the nostrils.

Treatment for brain AVMs can be symptomatic, and patients should be followed by a neurologist for any seizures, headaches, or focal neurologic deficits. AVM-specific treatment may also involve endovascular embolization, neurosurgery or radiosurgery.

Embolization, that is, cutting off the blood supply to the AVM with coils, particles, acrylates, or polymers introduced by a radiographically guided catheter, may be used in addition to neurosurgery or radiosurgery, but is rarely successful in isolation except in smaller AVMs. Gamma knife may also be used.

Simple surgical excision is curative. The recommended treatment is that the skin is peeled off the extra-auricular tissue and protruding cartilage remnants are trimmed. Normal appearance is achieved in majority of cases. The reconstruction successful in true cases of accessory auricle, as it also is in individuals with auricular appendages.

These lesions usually present in neonates, although they may not come to clinical attention until adulthood (for cosmetic reasons). There is no gender predilection. They are present in approximately 3-6 per 1000 live births.

The nature of this malformation remains unclear. Congenital, spontaneous, and acquired origins are accepted. The hypothesis of a spontaneous origin in the current case of SP is supported by no evidence of associated anomalies, such as cerebral aneurysmal venous malformations, systemic angiomas, venous angioma dural malformation, internal cerebral vein aneurysm, and cavernous hemangiomas.

CT and MRI are most often used to identify intracranial abnormalities. When a child is born with a facial cutaneous vascular malformation covering a portion of the upper or the lower eyelids, imaging should be performed to screen for intracranial leptomeningeal angiomatosis. The haemangioma present on the surface of the brain is in the vast majority of cases on the same side as the birth mark and gradually results in calcification of the underlying brain and atrophy of the affected region

The diagnosis is based on the combination of unusual facial features and the dysplastic or absent femurs.

Diagnosis may be made antenatally.

Diagnosis may be delayed for several months because the infant's early behavior appears to be relatively normal. Transillumination, an examination in which light is passed through body tissues, can be used to diagnose hydranencephaly. An accurate, confirmed diagnosis is generally impossible until after birth, though prenatal diagnosis using fetal ultrasonography (ultrasound) can identify characteristic physical abnormalities that exist. Through thorough clinical evaluation, via physical findings, detailed patient history, and advanced imaging techniques, such as angiogram, computerized tomography (CT scan), magnetic resonance imaging (MRI), or more rarely transillumination after birth are the most accurate diagnostic techniques. However, diagnostic literature fails to provide a clear distinction between severe obstructive hydrocephalus and hydranencephaly, leaving some children with an unsettled diagnosis.

Preliminary diagnosis may be made in utero via standard ultrasound, and can be confirmed with a standard anatomy ultrasound. This sometimes proves to provide a misdiagnosis of differential diagnoses including bilaterally symmetric schizencephaly (a less destructive developmental process on the brain), severe hydrocephalus (cerebrospinal fluid excess within the skull), and alobar holoprosencephaly (a neurological developmental anomaly). Once destruction of the brain is complete, the cerebellum, midbrain, thalami, basal ganglia, choroid plexus, and portions of the occipital lobes typically remain preserved to varying degrees. Though the cerebral cortex is absent, in most cases the fetal head remains enlarged due to the continued production by the choroid plexus of cerebrospinal fluid that is inadequately reabsorbed causing increased intracranial pressure.

Nevus psiloliparus is a cutaneous condition, a rare scalp anomaly characterized by a variable degree of alopecia and an excessive amount of adipose tissue.

It is the main hallmark of encephalocraniocutaneous lipomatosis (ECCL), otherwise known as Haberland syndrome.

When a patient has multiple abnormalities (multiple anomaly, multiple deformity), they have a congenital abnormality that can not be primarily identified with a single system of the body or single disease process. Most medical conditions can have systemic sequelae, but multiple abnormalities occur when the effects on multiple systems is immediately obvious.

Bier spots are small, light macules usually found on the arms and legs of young adults, in which the intervening skin may seem erthematous but blanches with pressure so that these light macules disappear. This is a benign physiologic vascular anomaly of no significance clinically.

Although it is possible for the birthmark and atrophy in the cerebral cortex to be present without symptoms, most infants will develop convulsive seizures during their first year of life. There is a greater likelihood of intellectual impairment when seizures are resistant to treatment. Studies do not support the widely held belief that seizure frequency early in life in patients who have SWS is a prognostic indicator.