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Saccular cerebral aneurysm

Dr Sajoscha Sorrentino and Dr Donna D'Souza et al.

Saccular cerebral aneurysms (also known as berry aneurysms) are intracranial aneurysms typically with a characteristic rounded shape and account for the vast majority of intracranial aneurysms. They are also the most common cause of non-traumatic subarachnoid haemorrhages. 

Epidemiology

Prevalence of saccular cerebral aneurysms in the asymptomatic general population has been reported over a wide range (0.2 - 8.9%) when examined angiographically, and in 15 - 30% of these patients, multiple aneurysms are found 4. 

A familial tendency to aneurysms is also well recognised, with patients who have more than one affect first degree relative affected having a 17 - 44% chance of themselves having an aneurysm 4. 

Pathology

The aneurysmal pouch is composed of thickened hyalinised intima with the muscular wall and internal elastic lamina being absent. As the aneurysm grows it may become irregular in outline, and may have mural thrombus. Typically rupture occurs from the dome 4.

Associations

Numerous associations have been identified, most relating to abnormal connective tissue. Associations include:

Location

Cerebral aneurysms typically occur at branch points, usually of sizable vessels, but sometimes at the origin of small perforators which may not be seen on imaging. Approximately 90% of such aneurysms arise from the anterior circulation 4. 

  • anterior circulation: ~ 90%
    • ACA / AComm complex: ~30 - 40%
    • supraclinioid ICA and ICA / PComm junction: ~30%
    • MCA (M1/M2 junction) bi/trifurcation: ~ 20 - 30%
  • posterior ciculation: ~ 10%
    • basilar tip
    • SCA
    • PICA

Radiographic features

Berry aneurysms can be imaged in a variety of methods: 

  1. CT angiography (CTA)
  2. MR angiography (MRA)
  3. digital subtraction (catheter) angiography (DSA)

Each of these confers certain advantages and disadvantages, although in general digital subtraction catheter angiography, especially with 3D acquisitions, is considered the gold standard in most institutions. 

Required description on a radiology report

Regardless of the modality used, a number of features need to be assessed to allow a decision in relation to treatment to be made. 

  • size : ideally 3 axis maximum size meansurements
  • neck : maximal width of the neck of the aneurysm
  • shape and lobulations
  • orientation : the direction in which the aneurysm points is often important in both
  • endovascular and surgical planning
  • any smaller branches in the vicinity of the aneurysm
  • any branch taking off from the aneurysm

Treatment and prognosis

Treatment of large or symptomatic aneurysms is with either endovascular coiling or surgical clipping. 

Management of small aneurysms is controversial. At less that 7mm in maximal diameter aneurysms are statistically unlikely to rupture, however due to their prevalence anyone working in the area has seen numerous patients with small aneurysms which have ruptured resulting in subarachnoid haemorrhage, often with devastating consequences. 

5 year cumulative risk of rupture of anterior circulation aneurysms 5:

  • < 7 mm : 0%
  • 7 - 12 mm : 2.6%
  • 13 - 24 mm : 14.5%
  • > 25 mm : 40%

5 year cumulative risk of rupture of posterior circulation aneurysms 5:

  • < 7 mm : 2.5%
  • 7 - 12 mm : 14.5%
  • 13 - 24 mm : 18.4%
  • > 25 mm : 50%

As such management will vary according to local experience, the location and appearance of the aneurysm, patient demographics etc... 

Differential diagnosis

When the abnormality has been confirmed to be vascular, the differential includes:

See also

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