Makindo Medical Notes

Related Subjects: |Hypertension |Subarachnoid Haemorrhage |Perimesencephalic Subarachnoid haemorrhage |Haemorrhagic stroke |Acute Stroke Assessment (ROSIER&NIHSS)

The main cause of subarachnoid haemorrhage (SAH) is a ruptured berry aneurysm. See the separate topic on the management of SAH for further details.

Introduction

• Saccular (Berry) aneurysms are developmental abnormalities in the blood vessels of the circle of Willis and its branches. They may be due to inherited connective tissue weakness, anatomical defects, and abnormal flow patterns.
• They are not detectable at birth or in childhood but may appear in early adulthood, enlarge, and become detectable in later life. They can remain silent lifelong, or in some patients, they may bleed and cause a subarachnoid haemorrhage (5% of all strokes).
• Found in 1-2% of the population, these aneurysms can cause local pressure effects, such as a third nerve palsy, or remain asymptomatic throughout life. Only a minority present with an acute bleed.
• This discussion should be read alongside the article on Subarachnoid Haemorrhage. Berry aneurysms are the most common cause of SAH but not the only one.

Images

Presentation

• Sudden "thunderclap" headache or collapse due to a bleed into the subarachnoid space. Immediate referral to a neurosurgeon is required.
• Saccular aneurysms cause 70-80% of non-traumatic SAH cases.
• Asymptomatic aneurysms may be detected during imaging for other reasons or via screening of first-degree relatives.
• Pressure symptoms may occur as aneurysms enlarge, potentially affecting cranial nerves (e.g., IIIrd nerve palsy due to posterior communicating artery aneurysm).

Anatomy

• Aneurysms have a neck and a dome (fundus), and their morphology can be assessed radiographically.
• They often form at arterial bifurcations and have a thickened hyalinised intima, with the muscular wall and internal elastic lamina absent at the neck.
• As aneurysms grow, they can become irregular and may develop mural thrombus, with the risk of rupture from the dome.

Risks

• Risk factors include age, smoking, and hypertension.
• Increased size, a history of prior SAH, cigarette smoking, and location in the basilar apex or posterior communicating artery increase rupture risk.

Associations

• Ehlers-Danlos syndrome (type IV), Marfan syndrome
• Autosomal dominant polycystic kidney disease (ADPKD)
• Coarctation of the aorta, bicuspid aortic valve
• Neurofibromatosis type 1 (NF1)
• Hereditary haemorrhagic telangiectasia
• Alpha 1 antitrypsin deficiency
• Cerebral AVM, fibromuscular dysplasia

Sites

Imaging Berry Aneurysms

• Non-contrast CT: Blood may be seen in the subarachnoid space during an acute SAH, and the aneurysm may be detected. A CTA should be done if possible.
• CT angiography (CTA): Useful to detect patent or thrombosed aneurysms. It shows aneurysms as hyperattenuating lesions, and thrombosis may be visualized as a filling defect.
• MRI angiography (MRA): MRI can detect patent aneurysms as flow voids or reveal heterogeneous signals in thrombosed aneurysms.
• Digital subtraction angiography (DSA): Gold standard, especially for small aneurysms, and offers 3D reconstructions for accurate measurement.

Treatment and Prognosis

Large or symptomatic aneurysms should be treated either by endovascular coiling or surgical clipping. Small aneurysms (<7 mm) are usually low-risk but can rarely rupture.

Treatment Options

• Clipping: Neurosurgical clipping requires a craniotomy and has a procedural mortality rate of 1-3%. It is effective for reducing the risk of rebleeding but carries a higher risk of vasospasm.
• Coiling: Endovascular coiling is a minimally invasive alternative that avoids craniotomy and offers a better outcome in selected patients. It is often preferred, though not always suitable due to anatomical constraints.
• Comparison: The ISAT trial showed better outcomes with coiling, with fewer patients dependent or dead at one year compared to clipping.

Fusiform Aneurysms

• Elongated, spindle-shaped aneurysms due to atherosclerosis, typically affecting the basilar artery.
• May cause neurological symptoms from compression but rarely rupture.

Mycotic Aneurysms

• Associated with endocarditis and caused by infected emboli lodging in cerebral arteries, leading to microinfarcts or abscesses.
• Rupture is rare, but treatment focuses on managing the underlying infection.