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.

Symptoms of AVM vary according to the location of the malformation. Roughly 88% of people with an AVM are asymptomatic; often the malformation is discovered as part of an autopsy or during treatment of an unrelated disorder (called in medicine an "incidental finding"); in rare cases, its expansion or a micro-bleed from an AVM in the brain can cause epilepsy, neurological deficit, or pain.

The most general symptoms of a cerebral AVM include headaches and epileptic seizures, with more specific symptoms occurring that normally depend on the location of the malformation and the individual. Such possible symptoms include:

- Difficulties with movement coordination, including muscle weakness and even paralysis;

- Vertigo (dizziness);

- Difficulties of speech (dysarthria) and communication, such as aphasia;

- Difficulties with everyday activities, such as apraxia;

- Abnormal sensations (numbness, tingling, or spontaneous pain);

- Memory and thought-related problems, such as confusion, dementia or hallucinations.

Cerebral AVMs may present themselves in a number of different ways:

- Bleeding (45% of cases)

- Acute onset of severe headache. May be described as the worst headache of the patient's life. Depending on the location of bleeding, may be associated with new fixed neurologic deficit. In unruptured brain AVMs, the risk of spontaneous bleeding may be as low as 1% per year. After a first rupture, the annual bleeding risk may increase to more than 5%.

- Seizure or brain seizure (46%) Depending on the place of the AVM, it can cause loss of vision in one place.

- Headache (34%)

- Progressive neurologic deficit (21%)

- May be caused by mass effect or venous dilatations. Presence and nature of the deficit depend on location of lesion and the draining veins.

- Pediatric patients

- Heart failure

- Macrocephaly

- Prominent scalp veins

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.

In the lungs, pulmonary arteriovenous malformations have no symptoms in up to 29% of all cases.

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.

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.

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.

The most common signs/symptoms of DAVFs are:

1. Pulsatile tinnitus

2. Occipital bruit

3. Headache

4. Visual impairment

5. Papilledema

Pulsatile tinnitus is the most common symptom in patients, and it is associated with transverse-sigmoid sinus DAVFs. Carotid-cavernous DAVFs, on the other hand, are more closely associated with pulsatile exophthalmos. DAVFs may also be asymptomatic (e.g. cavernous sinus DAVFs).

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.

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.

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".

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.

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.

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.

Vein of Galen aneurysmal malformations (VGAM) and Vein of Galen aneurysmal dilations (VGAD) are the most frequent arteriovenous malformations in infants and fetuses. VGAM consist of a tangled mass of dilated vessels supplied by an enlarged artery. The malformation increases greatly in size with age, although the mechanism of the increase is unknown. Dilation of the great cerebral vein of Galen is a secondary result of the force of arterial blood either directly from an artery via an arteriovenous fistula or by way of a tributary vein that receives the blood directly from an artery. There is usually a venous anomaly downstream from the draining vein that, together with the high blood flow into the great cerebral vein of Galen causes its dilation. The right sided cardiac chambers and pulmonary arteries also develop mild to severe dilation.

Clinical symptoms of CNS origin include recurrent headaches, focal neurological deficits, hemorrhagic stroke, and seizures, but CCM can also be asymptomatic. The nature and severity of the symptoms depend on the lesion's location.

Most commonly found adjacent to dural sinuses in the following locations:

1. Transverse (lateral) sinus, left-sided slightly more common than right

2. Intratentorial

3. From the posterior cavernous sinus, usually draining to the transverse or sigmoid sinuses

4. Vertebral artery (posterior meningeal branch)

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.

Major symptoms of PWS include:

Birthmarks: Effected PWS patients suffer from large, flat, pink staining on the skin. This staining is a result of the capillary malformations that have the tendency to increase the blood flow near the surface of the skin causing the staining. Because of the staining color they are sometimes referred to as “port-wine stains”. “Port-wine stain” or discoloration of the skin due to vascular malformation is also referred as Nevus flammeus.

Hypertrophy: Hypertrophy refers to excessive growth of the bone and soft tissue. In PWS patients a limb is overgrown and hypertrophy is usually seen in the affected limb.

Multiple arteriovenous fistulas: PWS patients also suffer from multiple AVFs that occur in conjunction with capillary malformations. AVFs occur because of abnormal connections between arteries and veins. Normally, blood flows from arteries to capillaries then to veins. But for AFV patients, because of the abnormal artery and vein connections, blood flows directly from arteries into the veins completely bypassing the capillaries. These irregular connections affect the blood circulation and may lead to life-threatening complications such as abnormal bleeding and heart failure. AVFs can be identified by: large, purplish bulging veins, swelling in limbs, decreased in blood pressure, fatigue and heart failure.

Capillary arteriovenous malformations: Vascular system disorder is the cause of the capillary malformations. Here, the capillaries are enlarged and increase the blood flow towards the surface of the skin. Because of the capillary malformations, the skin has multiple small, round, pink or even red dots. For most of the affected individuals, these malformations occur on the face, arms and or legs. The spots may be visible right from birth itself or they may develop during childhood years. If capillary malformations occur by themselves, it is not a huge threat to life. But when these occur in conjunction with AVFs then it is a clear indicator of PWS and may be serious depending on the severity of the malformations.

The Human Phenotype Ontology (HPO) reports of additional symptoms in PWS patients. HPO is an active database that collects and researches on the relationships between phenotypic abnormalities and biochemical networks. This is an useful database as it has information and data on some of the rarest diseases such as PWS. According to HPO, the symptoms which are reported very frequently in PWS patients include: abnormal bleeding, hypertrophy of the lower limb, hypertrophy of the upper limb, nevus flammeus or staining of the skin, peripheral arteriovenous fistula, telangiectasia of the skin. Frequent to occasional symptoms include: varicose veins, congestive heart failure, glaucoma and headache.

Abnormal bleeding: some skin lesions are prone to bleed easily.

Peripheral arteriovenous fistula: abnormal communication between artery and vein that is a direct result of the abnormal connection or wiring between the artery and vein.

Telangiectasia of the skin: Telangiectasia is a condition where tiny blood vessels become widened and form threadlike red lines and or patterns on the skin. Because of their appearance and formation of web-like patterns they are also known as spider veins. These patterns are referred as telangiectases.

Varicose veins: Enlarged, swollen and twisted veins.

Congestive heart failure: This is a condition in which the heart’s ability to meet the requirements of the body is diminished. The cardiac output is decreased and the amount of blood pumped is not adequate enough to keep the circulation from the body and lungs going.

Glaucoma: Glaucoma is a combination of diseases that cause damage to the optic nerve and may result in vision loss and blindness.

Headache: pain in the head.

Typically not diagnosed until late childhood or later, Bonnet–Dechaume–Blanc syndrome usually presents itself with a combination of central nervous system features (midbrain), ophthalmic features (retina), and facial features. The degree of expression of the syndrome's components varies both clinically and structurally. Common symptoms that lead to diagnosis are headaches, retro-orbital pain and hemianopia.

The ophthalmic features of the Bonnet–Dechaume–Blanc syndrome occur as retinal arteriovenous malformation (AVMs). There are three categories of AVMs that are categorized depending on the severity of the malformation. The first category consists of the patient having small lesions that usually are asymptomatic. The second category, more severe than the first, is when the patient’s malformation is missing a connecting capillary. The missing capillary is meant to serve as a link between an artery and a vein; without it, edemas, hemorrhages, and visual impairments can result. Category three, the most severe, occurs when the patient’s malformations are so severe that the dilated vessels cause no distinction between artery and vein. When the symptoms are this severe, the patient has a significantly increased risk of developing vision loss. Since the retinal lesions categorized vary from large vascular malformations that affect a majority of the retina to malformations that are barely visible, the lesions cause a wide range of symptoms including decrease in visual sharpness, proptosis, pupillary defects, optic degeneration and visual field defects. The most common type of visual field impairment due to AVMs is homonymous hemianopia. Homonymous hemianopia typically presents unilaterally, but bilateral cases have been reported as well.

The extent of the central nervous system (CNS) features/symptoms of Bonnet–Dechaume–Blanc syndrome is highly dependent of the location of the cerebral AVMs and the extent of the malformation. The most common symptom affecting the CNS is an intracranial hemangioma in the midbrain. Along with hemangiomas, the malformations result in severe headaches, cerebral hemorrhages, vomiting, meningism, seizures, acute strokes or progressive neurological deficits due to acute or chronic ischaemia caused by arteriovenous shunting.

The distinguishable facial features that result from Bonnet–Dechaume–Blanc syndrome vary from case to case. A person showing signs of the syndrome may display faint skin discoloration, nevi and angiomas of the skin. Some patients with this disorder also present with high flow arteriovenous malformations of the maxillofacial or mandibular (jaw) regions. Another facial indicator of this disease is malformations affecting the frontal and/or maxillary sinuses.

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.

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.

It is a vascular malformation wherein blood vessels proliferate along with accompanying mature fat and fibrous tissue, lymphatics and sometimes nerves. They may involve skin, subcutaneous tissue, skeletal muscle and occasionally bone.

Prognosis depends on the size and location of the tumour, untreated angiomatosis may lead to blindness and/ or permanent brain damage. Death may occur, with complications in the kidney or brain.

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.