A few studies have worked on providing details related to the outlook of disease progression. Two studies show that each year 0.5% of people who have never had bleeding from their brain cavernoma, but had symptoms of seizures, were affected by bleeding. In contrast, patients who have had bleeding from their brain cavernoma in the past had a higher risk of being affected by subsequent bleeding. The statistics for this are very broad, ranging from 4%-23% a year. Additional studies suggest that women and patients under the age of 40 are at higher risk of bleeding, but similar conducted studies did not reach the same conclusion. However, when cavernous hemangiomas are completely excised, there is very little risk of growth or rebleeding. In terms of life expectancy, not enough data has been collected on patients with this malformation in order to provide a representative statistical analysis.

The true incidence of cavernous hemangiomas is difficult to estimate because they are frequently misdiagnosed as other venous malformations. Cavernous hemangiomas of the brain and spinal cord (cerebral cavernous hemangiomas (malformations) (CCM)), can appear at all ages but usually occur in the third to fourth decade of a person's life with no sexual preference. In fact, CCM is present in 0.5% of the population. However, approximately 40% of those with malformations have symptoms. Asymptomatic individuals are usually individuals that developed the malformation sporadically, while symptomatic individuals usually have inherited the genetic mutation. The majority of diagnoses of CCM are in adults; however, 25% of cases of CCM are children. Approximately 5% of adults have liver hemangiomas in the United States, but most are asymptomatic. Liver hemangiomas usually occur between the ages of 30-50 and more commonly in women. Cases of infantile liver cavernomas are extremely rare. Cavernous hemangioma of the eye is more prevalent in women than men and between the ages of 20-40.

It is not known what percentage of people with IIH will remit spontaneously, and what percentage will develop chronic disease.

IIH does not normally affect life expectancy. The major complications from IIH arise from untreated or treatment-resistant papilledema. In various case series, the long-term risk of ones vision being significantly affected by IIH is reported to lie anywhere between 10 and 25%.

Factors increasing the risk of a subdural hematoma include very young or very old age. As the brain shrinks with age, the subdural space enlarges and the veins that traverse the space must travel over a wider distance, making them more vulnerable to tears. This and the fact that the elderly have more brittle veins make chronic subdural bleeds more common in older patients. Infants, too, have larger subdural spaces and are more predisposed to subdural bleeds than are young adults. For this reason, subdural hematoma is a common finding in shaken baby syndrome. In juveniles, an arachnoid cyst is a risk factor for a subdural hematoma.

Other risk factors for subdural bleeds include taking blood thinners (anticoagulants), long-term alcohol abuse, dementia, and the presence of a cerebrospinal fluid leak.

Intracerebral bleeds are the second most common cause of stroke, accounting for 10% of hospital admissions for stroke. High blood pressure raises the risks of spontaneous intracerebral hemorrhage by two to six times. More common in adults than in children, intraparenchymal bleeds are usually due to penetrating head trauma, but can also be due to depressed skull fractures. Acceleration-deceleration trauma, rupture of an aneurysm or arteriovenous malformation (AVM), and bleeding within a tumor are additional causes. Amyloid angiopathy is a not uncommon cause of intracerebral hemorrhage in patients over the age of 55. A very small proportion is due to cerebral venous sinus thrombosis.

Risk factors for ICH include:

- Hypertension (high blood pressure)

- Diabetes mellitus

- Menopause

- Cigarette smoking

- Excessive alcohol consumption

- Severe migraine

Traumautic intracerebral hematomas are divided into acute and delayed. Acute intracerebral hematomas occur at the time of the injury while delayed intracerebral hematomas have been reported from as early as 6 hours post injury to as long as several weeks.

IIAs are uncommon, accounting for 2.6% to 6% of all intracranial aneurysms in autopsy studies.

On average, IIH occurs in about one per 100,000 people, and can occur in children and adults. The median age at diagnosis is 30. IIH occurs predominantly in women, especially in the ages 20 to 45, who are four to eight times more likely than men to be affected. Overweight and obesity strongly predispose a person to IIH: women who are more than ten percent over their ideal body weight are thirteen times more likely to develop IIH, and this figure goes up to nineteen times in women who are more than twenty percent over their ideal body weight. In men this relationship also exists, but the increase is only five-fold in those over 20 percent above their ideal body weight.

Despite several reports of IIH in families, there is no known genetic cause for IIH. People from all ethnicities may develop IIH. In children, there is no difference in incidence between males and females.

From national hospital admission databases it appears that the need for neurosurgical intervention for IIH has increased markedly over the period between 1988 and 2002. This has been attributed at least in part to the rising prevalence of obesity, although some of this increase may be explained by the increased popularity of shunting over optic nerve sheath fenestration.

The risk of death from an intraparenchymal bleed in traumatic brain injury is especially high when the injury occurs in the brain stem. Intraparenchymal bleeds within the medulla oblongata are almost always fatal, because they cause damage to cranial nerve X, the vagus nerve, which plays an important role in blood circulation and breathing. This kind of hemorrhage can also occur in the cortex or subcortical areas, usually in the frontal or temporal lobes when due to head injury, and sometimes in the cerebellum.

For spontaneous ICH seen on CT scan, the death rate (mortality) is 34–50% by 30 days after the insult, and half of the deaths occur in the first 2 days. Even though the majority of deaths occurs in the first days after ICH, survivors have a long term excess mortality of 27% compared to the general population.

Mortality of IIA is high, unruptured IIA are associated with a mortality reaching 30%, while ruptured IIA has a mortality of up to 80%. IIAs caused by fungal infections have a worse prognosis than those caused by bacterial infection.

Arachnoid cysts are seen in up to 1.1% of the population with a gender distribution of 2:1 male:female Only 20% of these have symptoms, usually from secondary hydrocephalus.

A study that looked at 2,536 healthy young males found a prevalence of 1.7% (95% CI 1.2 to 2.3%). Only a small percentage of the detected abnormalities require urgent medical attention.

Subdural hematomas are most often caused by head injury, when rapidly changing velocities within the skull may stretch and tear small bridging veins. Subdural hematomas due to head injury are described as traumatic. Much more common than epidural hemorrhages, subdural hemorrhages generally result from shearing injuries due to various rotational or linear forces. Subdural hemorrhage is a classic finding in shaken baby syndrome, in which similar shearing forces classically cause intra- and pre-retinal hemorrhages. Subdural hematoma is also commonly seen in the elderly and in alcoholics, who have evidence of cerebral atrophy. Cerebral atrophy increases the length the bridging veins have to traverse between the two meningeal layers, hence increasing the likelihood of shearing forces causing a tear. It is also more common in patients on anticoagulants or antiplatelet drugs, such as warfarin and aspirin. Patients on these medications can have a subdural hematoma after a relatively minor traumatic event.

A further cause can be a reduction in cerebral spinal fluid pressure which can create a low pressure in the subarachnoid space, pulling the arachnoid away from the dura mater and leading to a rupture of the blood vessels.

Prognosis is also very poor when IVH results from intracerebral hemorrhage related to high blood pressure and is even worse when hydrocephalus follows. It can result in dangerous increases in ICP and can cause potentially fatal brain herniation. Even independently, IVH can cause morbidity and mortality. First, intraventricular blood can lead to a clot in the CSF conduits blocking its flow and leading to obstructive hydrocephalus which may quickly result in increased intracranial pressure and death. Second, the breakdown products from the blood clot may generate an inflammatory response that damages the arachnoid granulations, inhibiting the regular reabsorption of CSF and resulting in permanent communicating hydrocephalus.

Intracranial hemorrhage is a serious medical emergency because the buildup of blood within the skull can lead to increases in intracranial pressure, which can crush delicate brain tissue or limit its blood supply. Severe increases in intracranial pressure (ICP) can cause brain herniation, in which parts of the brain are squeezed past structures in the skull.

Nasal glial heterotopia is rare, while an encephalocele is uncommon. NGH usually presents in infancy, while encephalocele may present in older children and adults. It is seen in both genders equally.

Intracranial bleeding occurs when a blood vessel within the skull is ruptured or leaks. It can result from physical trauma (as occurs in head injury) or nontraumatic causes (as occurs in hemorrhagic stroke) such as a ruptured aneurysm. Anticoagulant therapy, as well as disorders with blood clotting can heighten the risk that an intracranial hemorrhage will occur.

A 1994 community-based study indicated that two out of every 100,000 people suffered from SCSFLS, while a 2004 emergency room-based study indicated five per 100,000. SCSFLS generally affects the young and middle aged; the average age for onset is 42.3 years, but onset can range from ages 22 to 61. In an 11-year study women were found to be twice as likely to be affected as men.

Studies have shown that SCSFLS runs in families and it is suspected that genetic similarity in families includes weakness in the dura mater, which leads to SCSFLS. Large scale population-based studies have not yet been conducted. While a majority of SCSFLS cases continue to be undiagnosed or misdiagnosed, an actual increase in occurrence is unlikely.

Brain contusions and subarachnoid hemorrhages are commonly associated with IVH. The bleeding can involve the anterior communicating artery or the posterior communicating artery.

In both adults and infants, IVH can cause dangerous increases in ICP, damage to the brain tissue, and hydrocephalus.

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.

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.

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.

Most arachnoid cysts are asymptomatic, and do not require treatment. Where complications are present, leaving arachnoid cysts untreated, may cause permanent severe neurological damage due to the progressive expansion of the cyst(s) or hemorrhage (bleeding). However, with treatment most individuals with symptomatic arachnoid cysts do well.

More specific prognoses are listed below:

- Patients with impaired preoperative cognition had postoperative improvement after surgical decompression of the cyst.

- Surgery can resolve psychiatric manifestations in selected cases.

In 2004 the first adequately large scale study on the natural history and long-term prognosis of this condition was reported; this showed that at 16 months follow-up 57.1% of patients had full recovery, 29.5%/2.9%/2.2% had respectively minor/moderate/severe symptoms or impairments, and 8.3% had died. Severe impairment or death were more likely in those aged over 37 years, male, affected by coma, mental status disorder, intracerebral hemorrhage, thrombosis of the deep cerebral venous system, central nervous system infection and cancer. A subsequent systematic review of nineteen studies in 2006 showed that mortality is about 5.6% during hospitalisation and 9.4% in total, while of the survivors 88% make a total or near-total recovery. After several months, two thirds of the cases has resolution ("recanalisation") of the clot. The rate of recurrence was low (2.8%).

In children with CVST the risk of death is high. Poor outcome is more likely if a child with CVST develops seizures or has evidence of venous infarction on imaging.

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.

Although surgery is the treatment of choice, it must be preceded by imaging studies to exclude an intracranial connection. Potential complications include meningitis and a cerebrospinal fluid leak. Recurrences or more correctly persistence may be seen in up to 30% of patients if not completely excised.

Final outcomes for people with SCSFLS remain poorly studied. Symptoms may resolve in as little as two weeks, or persist for months. Less commonly, patients may suffer from unremitting symptoms for many years. People with chronic SCSFLS may be disabled and unable to work. Recurrent CSF leak at an alternate site after recent repair is common.