Intracranial Aneurysms

About intracranial Aneurysms

• Studies to date show peaks at various ages in the 40- to 70-year range.
• Most studies show an average age, approximately 46 to 47 years.
• Men have a lower average age at time of rupture than do women.
• The difference between men and women range from 2 to 4 years; the reasons for this are unclear

Autopsy studies of patients who died acutely from a ruptured intracranial aneurysm have made significant contributions to our understanding of the nature, location and factors related to their demise.

• The rate of ruptured cerebral aneurysms in sudden natural deaths is 1.5%-4%.
• In the majority of cases, patients reported no symptoms before the aneurysm ruptured.
• Where there was a symptom, it was often a headache in 25-27% of cases.

The findings appear to indicate that whereas there is a classic sudden and severe headache that heralds the rupture of a cerebral aneurysm, most symptoms, when present, are often vague and difficult to directly associate with the ruptured aneurysm before the diagnosis. Neurologic symptoms were infrequent. Most patients were asleep when the rupture occurred and even most of the active circumstances noted did not involve extraordinary physical exertion.

The major causes of sudden death are as follows:

• Raised intracranial pressure
• Brain stem compression
• Pulmonary complications.

Location and size of Aneurysms

• The middle cerebral artery and the anterior communicating artery are the most common vessels involved in aneurysms (either singly or as part of a branch point).
• The rate of occurrence of multiple aneurysms is 9%-34%. Average 20% in cases with SAH
• The majority of aneurysms were small; of range less than 5mm in 60% of cases.
• In ruptured aneurysms, the sizes were more commonly 6-9mm.

Aneurysms can be single or multiple. There is a significant association between the presence of multiple aneurysms and hypertension (p < 0.001), cigarette smoking (p < 0.001), family history of cerebrovascular disease (p < 0.001), female sex (p < 0.001), and postmenopausal state in female patients (p < 0.001).

Aneurysms can occur in any age group though most commonly in adults aged from 40-60 years. In children and young adults, intracranial saccular aneurysms are rare neurosurgical lesions, occurring in 1-3% of large epidemiological aneurysm series. There is a predominant male:female ratio approaching 2:1 different to the 1:2 ratio in adults. Furthermore, a disproportionately high number of these aneurysms arise at peripheral locations on the arterial tree and are large or even giant aneurysms. See example of a giant aneurysm

The danger of rupture

A ruptured intracranial aneurysm can cause bleeding into the subarachnoid spaces (SAH), into the brain (ICH), or very rarely into the subdural space. CT scan of a patient who presented with the classical symptoms of subarachnoid haemorrhage. The CT scan reveals blood in the cisterns and likely in the ventricles (3rd & 4th) which would make this a Fisher Grade 4 rather than a 2 as shown. The amount of blood in the CSF spaces is significant but widely spread. The source cannot be determined on the basis of the CT scan. Angiogram was performed as shown below. The basilar aneurysm shown on angio above caused the SAH bleed.

See, for comparison, the normal vetebrobasilar anatomy on the left and the basilar tip aneurysm on the right. You might be able to appreciate this better with a coloured 3D image on MRA. The aneurysm is coloured red.

Acute aneurysmal subdural haemorrhage occurs very rarely. However, it is fraught with additional and significant dangers for the patient.

What are the relevant statistics?

• Subarachnoid Haemorrhage occurs in approximately 5% of stroke cases.
• A ruptured aneurysm is the cause in about 75% of cases and no cause found in 20%.
  In 0.5%-7.9% of patients presenting with a ruptured aneurysm, there is an acute subdural haematoma (SDH).
• A ruptured posterior communicating artery aneurysm is often found on cerebral angiography.

The presentation in these cases follow similar lines as for SAH- sudden, severe headache and collapse with varying levels of loss of consciousness. The SDH should be suspected as due to an underlying abnormality if there is no history of trauma. The other causes of an acute SDH apart from trauma are blood dyscrasias, infections and carcinomatosis.

There are three theories related to the development of the SDH

1. Adhesions exists between the sac of the aneurysm and the arachnoid layer so any further bleed ruptures into the subdural space.
2. The arachnoid is ruptured in a major bleed by the force of the ejecting blood.
3. The SDH occurs through brain laceration from a large intracerebral haematoma.

An acute SDH may be the only CT finding but it may also be associated with a large ICH.

Surgical evacuation of a large life-threatening SDH and clipping or coiling of the aneurysm must be undertaken as an emergency. In a previous review of the literature of cases of aneurysmal SDH, only cases with the aneurysm treated, either surgically or endovascularly, survived. Patients who had just the clot evacuated had a poor outcome.

Aneurysmal Subarachnoid Haemorrhage

• Subarachnoid haemorrhage (SAH) is a type of stroke.
• It is an haemorrhagic stroke and occurs in only 5% of cases of stroke.
  The other significant haemorrhagic stroke subtype is the spontaneous intracerebral haemorrhage (ICH) which is found in approximately 15% of case.
• The annual incidence of SAH varies in many populations between 6-10/100,000
  The incidence is very low in India.
• The recorded highest incidence is in Finland (up to 20/100,000).
• SAH can sometimes be associated with an ICH. This occurs most commonly with a middle cerebral artery aneurysm but any aneurysm can also present in this way (see example).

• In 20% of cases of SAH, no aneurysm is discovered- sometimes called perimesencephalic SAH.

Aneurysms can be treated through a wide variety of ways and means ranging through endovascular and surgical techniques.

Surgery is the gold-standard in the management of aneurysms although many aneurysms especially in the posterior circulation are more frequently treated by endovascular means. Surgery entails direct exposure of the aneurysm, the parent vessel(s) and surrounding structures. The aneurysm is then secured by the placement of a metallic clip along the neck thereby excluding the sac/fundus from the circulation.

Some aneurysms can be managed by bypass surgery and some can be simply wrapped with muslin etc. Wrapping, though still carried out by many surgeons, is not a preferred option.

Certain intracranial aneurysms, because of their fusiform or complex wide-necked structure, giant size, or involvement with critical perforating or branch vessels are not amenable to direct surgical clipping or endovascular coil treatment.

Endovascular Coiling of Aneurysms
Endovascular coiling of aneurysms offer a safe, effective and viable alternative to surgery. Although surgery remains the gold-standard, endovascular therapy is gradually replacing surgery for certain aneurysms notably those of the posterior circulation. Surgery is still required for patients with aneurysms considered unsuitable for endovascular approach, such as those with wide necks, fusiform aneurysms, complex aneurysm with unclear anatomy and those smaller than 2mm in size.

The procedure of coiling has been described in many reports. The embolisation procedures can be performed following access through either femoral arteries to the common carotid or vertebral arteries. A microcatheter (Tracker-10 or 18; Target Therapeutics, Fremont, California, USA) etc. are used for access to the aneurysm and Guglielmi Detachable Coils (GDC) (Target Therapeutics, Fremont, California, USA). The aneurysm sac is filled with the coils until the lumen was occluded completely

Created by B I Ogungbo in September 2002. Modified January 2008. ©