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.

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.

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

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

CCF symptoms include bruit (a humming sound within the skull due to high blood flow through the arteriovenous fistula), progressive visual loss, and pulsatile proptosis or progressive bulging of the eye due to dilatation of the veins draining the eye. Pain is the symptom that patients often find the most difficult to tolerate.

Patients usually present with sudden or insidious onset of redness in one eye, associated with progressive proptosis or bulging.

They may have a history of similar episodes in the past.

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).

Carotid cavernous fistulae may form following closed or penetrating head trauma, surgical damage, rupture of an intracavernous aneurysm, or in association with connective tissue disorders, vascular diseases and dural fistulas.

d vessels can present a large variety of , and/or . The effects may range from a change in blood pressure to an interruption in circulation, depending on the nature and degree of the misplacement and which vessels are involved.

Although "transposed" literally means "swapped", many types of TGV involve vessels that are in abnormal positions, while not actually being swapped with each other. The terms TGV and TGA are most commonly used in reference to dextro-TGA – in which the arteries "are" in swapped positions; however, both terms are also commonly used, though to a slightly lesser extent, in reference to levo-TGA – in which both the arteries and the ventricles are swapped; while other defects in this category are almost never referred to by either of these terms.

In dextro-Transposition of the great arteries (dextro-TGA) deoxygenated blood from the right heart is pumped immediately through the aorta and circulated to the body and the heart itself, bypassing the lungs altogether, while the left heart pumps oxygenated blood continuously back into the lungs through the pulmonary artery. In effect, two separate "circular" (parallel) circulatory systems are created. It is called a cyanotic congenital heart defect (CHD) because the newborn infant turns blue from lack of oxygen.

An arteriovenous fistula is an abnormal connection or passageway between an artery and a vein. It may be congenital, surgically created for hemodialysis treatments, or acquired due to pathologic process, such as trauma or erosion of an arterial aneurysm.

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)

Just like berry aneurysm, an intracerebral arteriovenous fistula can rupture causing subarachnoid hemorrhage.

A Cimino fistula, also Cimino-Brescia fistula, surgically created arteriovenous fistula and (less precisely) arteriovenous fistula (often abbreviated AV fistula or AVF), is a type of vascular access for hemodialysis. It is typically a surgically created connection between an artery and a vein in the arm, although there have been acquired arteriovenous fistulas which do not in fact demonstrate connection to an artery.

Surgically created AV fistulas work effectively because they:

- Have high volume flow rates (as blood takes the path of least resistance; it prefers the (low resistance) AV fistula over traversing (high resistance) capillary beds).

- Use native blood vessels, which, when compared to synthetic grafts, are less likely to develop stenoses and fail.

A paradoxical embolism, also called a crossed embolism, refers to an embolus which is carried from the venous side of circulation to the arterial side, or vice versa. It is a kind of stroke or other form of arterial thrombosis caused by embolism of a thrombus (blood clot), air, tumor, fat, or amniotic fluid of venous origin, which travels to the arterial side through a lateral opening in the heart, such as a patent foramen ovale, or arteriovenous shunts in the lungs.

The opening is typically an atrial septal defect, but can also be a ventricular septal defect.

Paradoxical embolisms represent two percent of arterial emboli.

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.

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.

It involves three major defects:

- A failure of the diaphragm to completely close during development

- Herniation of the abdominal contents into the chest

- Pulmonary hypoplasia

The Bochdalek hernia, also known as a postero-lateral diaphragmatic hernia, is the most common manifestation of CDH, accounting for more than 95% of cases. In this instance the diaphragm abnormality is characterized by a hole in the postero-lateral corner of the diaphragm which allows passage of the abdominal viscera into the chest cavity. The majority of Bochdalek hernias (80–85%) occur on the left side of the diaphragm, a large proportion of the remaining cases occur on the right side. To date, it carries a high mortality and an active area of clinical research.

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.

A cerebral arteriovenous malformation (cerebral AVM, CAVM, cAVM) is an abnormal connection between the arteries and veins in the brain—specifically, an arteriovenous malformation in the cerebrum.

Passage of a clot (thrombus) from a systemic vein to a systemic artery. When clots in systemic veins break off (embolize), they travel first to the right side of the heart and, normally, then to the lungs where they lodge, causing pulmonary embolism. On the other hand, when there is a hole at the septum, either upper chambers of the heart (an atrial septal defect) or lower chambers of the heart (ventricular septal defects), a clot can cross from the right to the left side of the heart, then pass into the systemic arteries as a paradoxical embolism. Once in the arterial circulation, a clot can travel to the brain, block a vessel there, and cause a stroke (cerebrovascular accident).

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.

The symptoms of pulmonary hypertension include the following:

Less common signs/symptoms include non-productive cough and exercise-induced nausea and vomiting. Coughing up of blood may occur in some patients, particularly those with specific subtypes of pulmonary hypertension such as heritable pulmonary arterial hypertension, Eisenmenger syndrome and chronic thromboembolic pulmonary hypertension. Pulmonary venous hypertension typically presents with shortness of breath while lying flat or sleeping (orthopnea or paroxysmal nocturnal dyspnea), while pulmonary arterial hypertension (PAH) typically does not.

Other typical signs of pulmonary hypertension include an accentuated pulmonary component of the second heart sound, a right ventricular third heart sound, and parasternal heave indicating a hypertrophied right atrium. Signs of systemic congestion resulting from right-sided heart failure include jugular venous distension, ascites, and hepatojugular reflux. Evidence of tricuspid insufficiency and pulmonic regurgitation is also sought and, if present, is consistent with the presence of pulmonary hypertension.

The most frequently observed problems, related to an AVM, are headaches and seizures, backaches, neckaches and eventual nausea, as the coagulated blood makes its way down to be dissolved in the individual's spinal fluid. It is supposed that 15% of the population, at detection, have no symptoms at all. Other common symptoms are a pulsing noise in the head, progressive weakness and numbness and vision changes as well as debilitating, excruciating pain.

In serious cases, the blood vessels rupture and there is bleeding within the brain (intracranial hemorrhage). Nevertheless, in more than half of patients with AVM, hemorrhage is the first symptom. Symptoms due to bleeding include loss of consciousness, sudden and severe headache, nausea, vomiting, incontinence, and blurred vision, amongst others. Impairments caused by local brain tissue damage on the bleed site are also possible, including seizure, one-sided weakness (hemiparesis), a loss of touch sensation on one side of the body and deficits in language processing (aphasia). Ruptured AVMs are responsible for considerable mortality and morbidity.

AVMs in certain critical locations may stop the circulation of the cerebrospinal fluid, causing accumulation of the fluid within the skull and giving rise to a clinical condition called hydrocephalus. A stiff neck can occur as the result of increased pressure within the skull and irritation of the meninges.