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Intracranial Aneurysm

Summary

  • Focal dilatation of cerebral artery wall, typically at branching points
  • Risk of rupture leading to subarachnoid haemorrhage
  • Diagnosis primarily through imaging, treatment options include surgical clipping and endovascular coiling1

Pathophysiology

  • Weakening of arterial wall due to haemodynamic stress and structural abnormalities
  • Common locations: anterior communicating artery, posterior communicating artery, middle cerebral artery bifurcation
  • Risk factors for formation:
    • Genetic predisposition (e.g., polycystic kidney disease)
    • Hypertension
    • Smoking
    • Excessive alcohol consumption

Demographics

  • Prevalence: 3-5% of general population
  • More common in females (1.6:1 ratio)
  • Peak incidence of rupture: 40-60 years old
  • Higher prevalence in certain populations:
    • Finnish and Japanese populations
    • First-degree relatives of patients with intracranial aneurysms

Diagnosis

  • Often asymptomatic until rupture
  • Symptoms of unruptured aneurysms:
    • Headache
    • Cranial nerve palsies
    • Seizures
  • Ruptured aneurysm presentation:
    • Sudden, severe headache ("thunderclap headache")
    • Neck stiffness
    • Photophobia
    • Altered consciousness
  • Diagnostic tools:
    • CT angiography (CTA)
    • Magnetic Resonance Angiography (MRA)
    • Digital Subtraction Angiography (DSA)

Imaging

  • CT without contrast:
    • Acute subarachnoid haemorrhage: hyperdense blood in subarachnoid spaces
    • Calcification in aneurysm wall
  • CTA:
    • High sensitivity (77-97%) and specificity (87-100%) for aneurysms >3mm
    • Allows 3D reconstruction for surgical planning
  • MRA:
    • Time-of-Flight (TOF) technique: high sensitivity for aneurysms >3mm
    • Contrast-enhanced MRA: improved detection of small aneurysms
  • DSA:
    • Gold standard for diagnosis and characterization
    • Allows dynamic assessment of flow and collateral circulation

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  • An MRI in a patient with a longstanding left lateral rectus palsy showed a 1.2 cm cavernous ICA aneurysm interfering with the left abducens nerve.
  • The left lateral rectus was atrophic.

Treatment

  • Ruptured aneurysms are secured by endovascular coiling/flow diversion or surgical clipping
  • Small unruptured aneurysms are often surveilled; rupture risk rises with size, posterior circulation location and growth

Differential diagnosis

Differential Diagnosis Differentiating Feature
Arteriovenous Malformation Presence of feeding arteries and draining veins on angiography
Cavernous Malformation Characteristic "popcorn" appearance on MRI
Meningioma Extra-axial location and dural tail sign on MRI
Pituitary Adenoma Sellar/suprasellar location; no flow voids; enhances homogeneously
Glioma Infiltrative appearance with surrounding oedema; no flow void or arterial origin
Metastasis Multiple lesions at grey-white junction; no flow void; ring or nodular enhancement
Cerebral Abscess Ring-enhancing lesion with restricted diffusion on MRI
Thrombosed Giant Aneurysm Layered appearance on MRI with varying signal intensities
Developmental Venous Anomaly Characteristic "caput medusae" appearance on contrast-enhanced imaging
Capillary Telangiectasia Faint enhancement on MRI without mass effect

  1. Allaw et al. A Review of Intracranial Aneurysm Imaging Modalities, from CT to State-of-the-Art MR. 2025. AJNR. American journal of neuroradiology - Open in new tab. ↩