Spontaneous cases are considered to be caused by intrinsic factors that weaken the arterial wall. Only a very small proportion (1–4%) have a clear underlying connective tissue disorder, such as Ehlers–Danlos syndrome type 4 and more rarely Marfan's syndrome. Ehlers-Danlos syndrome type 4, caused by mutations of the "COL3A" gene, leads to defective production of the collagen, type III, alpha 1 protein and causes skin fragility as well as weakness of the walls of arteries and internal organs. Marfan's syndrome results from mutations in the "FBN1" gene, defective production of the protein fibrillin-1, and a number of physical abnormalities including aneurysm of the aortic root.

There have also been reports in other genetic conditions, such as osteogenesis imperfecta type 1, autosomal dominant polycystic kidney disease and pseudoxanthoma elasticum, α antitrypsin deficiency and hereditary hemochromatosis, but evidence for these associations is weaker. Genetic studies in other connective tissue-related genes have mostly yielded negative results. Other abnormalities to the blood vessels, such as fibromuscular dysplasia, have been reported in a proportion of cases. Atherosclerosis does not appear to increase the risk.

There have been numerous reports of associated risk factors for vertebral artery dissection; many of these reports suffer from methodological weaknesses, such as selection bias. Elevated homocysteine levels, often due to mutations in the "MTHFR" gene, appear to increase the risk of vertebral artery dissection. People with an aneurysm of the aortic root and people with a history of migraine may be predisposed to vertebral artery dissection.

Prognosis of spontaneous cervical arterial dissection involves neurological and arterial results. The overall functional prognosis of individuals with stroke due to cervical artery dissection does not appear to vary from that of young people with stroke due to other causes. The rate of survival with good outcome (a modified Rankin score of 0–2) is generally about 75%, or possibly slightly better (85.7%) if antiplatelet drugs are used. In studies of anticoagulants and aspirin, the combined mortality with either treatment is 1.8–2.1%.

After the initial episode, 2% may experience a further episode within the first month. After this, there is a 1% annual risk of recurrence. Those with high blood pressure and dissections in multiple arteries may have a higher risk of recurrence. Further episodes of cervical artery dissection are more common in those who are younger, have a family history of cervical artery dissection, or have a diagnosis of Ehlers-Danlos syndrome or fibromuscular dysplasia.

70% of patients with carotid arterial dissection are between the ages of 35 and 50, with a mean age of 47 years.

Incidence rates of cranial aneurysms are estimated at between 0.4% and 3.6%. Those without risk factors have expected prevalence of 2–3%. In adults, females are more likely to have aneurysms. They are most prevalent in people ages 35 – 60, but can occur in children as well. Aneurysms are rare in children with a reported prevalence of .5% to 4.6%. The most common incidence are among 50-year-olds, and there are typically no warning signs. Most aneurysms develop after the age of 40.

Incidence rates are two to three times higher in males, while there are more large and giant aneurysms and fewer multiple aneurysms. Intracranial hemorrhages are 1.6 times more likely to be due to aneurysms than cerebral arteriovenous malformations in whites, but four times less in certain Asian populations.

Most patients, particularly infants, present with subarachnoid hemorrhage and corresponding headaches or neurological deficits. The mortality rate for pediatric aneurysms is lower than in adults.

Once considered uncommon, spontaneous carotid artery dissection is an increasingly recognised cause of stroke that preferentially affects the middle-aged.

The incidence of spontaneous carotid artery dissection is low, and incidence rates for internal carotid artery dissection have been reported to be 2.6 to 2.9 per 100,000.

Observational studies and case reports published since the early 1980s show that patients with spontaneous internal carotid artery dissection may also have a history of stroke in their family and/or hereditary connective tissue disorders, such as Marfan syndrome, Ehlers-Danlos syndrome, autosomal dominant polycystic kidney disease, pseudoxanthoma elasticum, fibromuscular dysplasia, and osteogenesis imperfecta type I. IgG4-related disease involving the carotid artery has also been observed as a cause.

However, although an association with connective tissue disorders does exist, most people with spontaneous arterial dissections do not have associated connective tissue disorders. Also, the reports on the prevalence of hereditary connective tissue diseases in people with spontaneous dissections are highly variable, ranging from 0% to 0.6% in one study to 5% to 18% in another study.

Internal carotid artery dissection can also be associated with an elongated styloid process (known as Eagle syndrome when the elongated styloid process causes symptoms).

Intracranial aneurysms may result from diseases acquired during life, or from genetic conditions. Lifestyle diseases including hypertension, smoking, excessive alcoholism, and obesity are associated with the development of brain aneurysms. Cocaine use has also been associated with the development of intracranial aneurysms.

Other acquired associations with intracranial aneurysms include head trauma and infections.

The prevalence of intracranial aneurysm is about 1-5% (10 million to 12 million persons in the United States) and the incidence is 1 per 10,000 persons per year in the United States (approximately 27,000), with 30- to 60-year-olds being the age group most affected. Intracranial aneurysms occur more in women, by a ratio of 3 to 2, and are rarely seen in pediatric populations.

Mortality from aortic rupture is up to 90%. 65–75% of patients die before they arrive at hospital and up to 90% die before they reach the operating room.

There is evidence to suggest that a major cause of spontaneous coronary artery dissection (SCAD) is related to female hormone levels, as most cases appear to arise in pre-menopausal women, although there is evidence that the condition can have various triggers. Other underlying conditions such as hypertension, recent delivery of a baby, fibromuscular dysplasia and connective-tissue disorders (e.g., Marfan syndrome and Ehlers-Danlos syndrome) may occasionally result in SCAD. There is also a possibility that vigorous exercise can be a trigger. However, many cases have no obvious cause.

Examples include:

- Aortic dissection (aorta)

- Coronary artery dissection (coronary artery)

- Carotid artery dissection (carotid artery)

- Vertebral artery dissection (vertebral artery)

Carotid and vertebral artery dissection are grouped together as "cervical artery dissection".

Establishing the incidence of aortic dissection has been difficult because many cases are only diagnosed after death (which may have been attributed to another cause), and is often initially misdiagnosed. Aortic dissection affects an estimated 2.0–3.5 people per every 100,000 every year. Studies from Sweden suggest that the incidence of aortic dissection may be rising. Men are more commonly affected than women: 65% of all people with aortic dissection are male. The mean age at diagnosis is 63 years. In females before the age of 40, half of all aortic dissections occur during pregnancy (typically in the third trimester or early postpartum period).

Of all people with aortic dissection, 40% die immediately and do not reach a hospital in time. Of the remainder, 1% die every hour, making prompt diagnosis and treatment a priority. Even after diagnosis, 5–20% die during surgery or in the immediate postoperative period. In ascending aortic dissection, if surgery is decided to be not appropriate, 75% die within 2 weeks. With aggressive treatment, 30-day survival for thoracic dissections may be as high as 90%.

In medical pathology, a dissection is a tear within the wall of a blood vessel, which allows blood to separate the wall layers. By separating a portion of the wall of the artery (a layer of the tunica intima or tunica media), a dissection creates two lumens or passages within the vessel, the native or true lumen, and the "false lumen" created by the new space within the wall of the artery.

While the cause of FMD remains unclear, current theory suggest that there may be a genetic predisposition as case reports have identified clusters of the disease and prevalence among twins. In fact, according to the Cleveland Clinic approximately 10% of cases appear to be inherited and often coexists with other genetic abnormalities that affect the blood vessels. Approximately 10% of patients with FMD have an affected family member. A study conducted from the patient registry at Michigan Cardiovascular Outcomes Research and Reporting Program (MCORRP) at the University of Michigan Health System reported a high prevalence of a family history of stroke (53.5%), aneurysm (23.5%), and sudden death (19.8%). Even though FMD is a non-atherosclerotic disease family histories of hypertension and hyperlipidemia were also common among those diagnosed with FMD. It is believed that the cause of FMD is not a single identifier such as genetics but has multiple underlying factors. Theories of hormonal influence, mechanical stress from trauma and stress to the artery walls, and also the effect of loss of oxygen supply to the blood vessel wall caused by fibrous lesions. It has been suggested that environmental factors, such as smoking and estrogen, may play role in addition to genetic factors.

Coronary artery dissection results from a tear in the inner layer of the artery, the tunica intima. This allows blood to penetrate and cause an intramural hematoma in the central layer, the tunica media, and a restriction in the size of the lumen, resulting in reduced blood flow which in turn causes myocardial infarction and can later cause sudden cardiac death.

The major cause of acute limb ischaemia is arterial thrombosis (85%), while embolic occlusion is responsible for 15% of cases. In rare instances, arterial aneurysm of the popliteal artery has been found to create a thrombosis or embolism resulting in ischaemia.

Hypertension and cigarette smoking are the most important risk factors, though the importance of genetic factors has been increasingly recognized. Approximately 10% of patients may have other family members who have aortic aneurysms. It is also important to note that individuals with a history of aneurysms in other parts of the body have a higher chance of developing a thoracic aortic aneurysm.

Each year in the United States, some 45,000 people die from diseases of the aorta and its branches. Acute aortic dissection, a life-threatening event due to a tear in the aortic wall, affects 5 to 10 patients per million population each year, most often men between the ages of 50 and 70; of those that occur in women younger than 40, nearly half arise during pregnancy. The majority of these deaths occur as a result of complications of thoracic aneurysmal disease.

The incidence of myocardial rupture has decreased in the era of urgent revascularization and aggressive pharmacological therapy for the treatment of an acute myocardial infarction. However, the decrease in the incidence of myocardial rupture is not uniform; there is a slight increase in the incidence of rupture if thrombolytic agents are used to abort a myocardial infarction. On the other hand, if primary percutaneous coronary intervention is performed to abort the infarction, the incidence of rupture is significantly lowered. The incidence of myocardial rupture if PCI is performed in the setting of an acute myocardial infarction is about 1 percent.

The most common cause of aortic rupture is a ruptured aortic aneurysm. Other causes include trauma and iatrogenic (procedure-related) causes.

The natural history of this disorder is not well known. The long term outlook for patients with treated moyamoya seems to be good. While symptoms may seem to improve almost immediately after the in-direct EDAS, EMS, and multiple burr holes surgeries, it will take probably 6–12 months before new vessels can develop to give a sufficient blood supply. With the direct STA-MCA surgery, increased blood supply is immediate.

Once major stroke or bleeding take place, even with treatment, the patient may be left with permanent loss of function so it is very important to treat this condition promptly.

Dr. Michael Scott, MD discusses the success rate for Moyamoya surgery in

The incidence of VBI increases with age and typically occurs in the seventh or eighth decade of life. Reflecting atherosclerosis, which is the most common cause of VBI, it affects men twice as often as women and patients with hypertension, diabetes, smoking, and dyslipidemias have a higher risk of developing VBI.

VBI, often provoked by sudden and temporary drops in blood pressure, can cause transient ischemic attacks. Postural changes (see orthostatic hypotension), such as getting out of bed too quickly or standing up after sitting for extended periods of time, often provoke these attacks. Exercise of the legs, or the sudden cessation of leg exercises, may also bring on the symptoms of VBI. For the sedentary older subject, going up a flight of stairs or walking the dog may be enough to cause pooling of blood in the legs and a drop in blood pressure in the distal arteries of the head. Heat and dehydration may also be contributing causes.

Mechanical forces acting upon the neck at any age can cause VBI by exacerbating arterial insufficiency or outright occluding one or both vertebrobasilar arteries. Internal forces include those caused by turning the head to an extreme angle to the side, especially with the neck extended. The patient can create this condition while driving a vehicle in reverse, shooting a bow and arrow, bird watching, or stargazing. There was a study demonstrating the relationship between VBI and yoga practice, though this subject is in need of updated research. External forces include those caused by sports or other physical contact.

Recent investigations have established that both moyamoya disease and arteriovenous fistulas (AVFs) of the lining of the brain, the dura, are associated with dural angiogenesis. These factors may represent a mechanism for ischemia contributing to the formation of dural AVFs. At least one case of simultaneous unilateral moyamoya syndrome and ipsilateral dural arteriovenous fistula has been reported at the Barrow Neurological Institute. In this case a 44-year-old man presented with headache, tinnitus, and an intraventricular hemorrhage, as seen on computed tomographic scans. Cerebral angiography showed a right moyamoya pattern and an ipsilateral dural AVF fed by branches of the external carotid artery and draining into the transverse sinus. This extremely rare coincidental presentation may have deeper pathogenic implications.

Inheritance is thought to be rather complex. There is a good amount of evidence that shows the disease is autosomal dominant, with some penetrance. There is also the possibility of age related dependence. It is known that Marfan’s Syndrome and Ehler-Danlos Syndrome lead to an increased risk for development of FAD. Marfan’s Syndrome is not required to have an aortic dissection. One study suggests that the chromosomal locus for the gene is 5q13-14. The same study found that other genes may be linked, and include loci for Marfan and Ehler-Danlos Syndromes, genes for metalloproteinase 3 and 9, and tissue inhibitor of malloproteinase 2 as well as two loci on chromosomes 5q13-14 and lq23.2-24. Still other studies show that mutations in smooth muscle cell-specific isoforms of alpha actin and beta myosin heavy chain may cause FAD. Mutations in the genes TGFBR 1 and 2 are known to cause dissections in aortas with normal diameter size (>4.3 cm) and gene "FPN1" mutations typically affect aortas with larger diameters (<4.4 cm).

There are several hypotheses which attempt to explain how the dissection physically occurs. The first states that a tear develops in the intima layer of the aorta which allows blood to flow from the lumen of the aorta into the intima. This event creates a dissection and essentially two lumens. The second hypothesis suggests that the vasa vasorum ruptures and causes a hemorrhage in the wall of the aorta. The hemorrhaging promotes tearing of the intima and eventually aortic dissection.

The major risk factors for FAD include high blood pressure, old age, haematoma, genetic weakening of aortic wall, cocaine use, pregnancy and diseases causing abnormal connective tissue. One study found that the average age(s) for the occurrence of dissection caused by degenerative aneurysm is 65 years and up. Dissections thought to be the result of genetic mutations appear to be more likely to occur between the ages of 40 and 60. Another study found that 20% of patients with FAD have a close relative with a history of thoracic aortic aneurysm or dissection which suggests yet another major risk factor.