Feature Article

Cerebral aneurysms and subarachnoid haemorrhage: avoiding the diagnostic pitfalls

Nicholas Little, Heath French



Patients with atypical or mild symptoms of subarachnoid haemorrhage due to a ruptured cerebral aneurysm are more difficult to diagnose than patients who present with typical symptoms of sudden severe headache and associated symptoms. Patients without typical symptoms are more likely to have low volume haemorrhages that may not be seen on a CT scan.

Key Points

  • Subarachnoid haemorrhage (SAH) due to a ruptured cerebral aneurysm is a potentially fatal condition that often presents as headache.
  • A raised index of suspicion must exist for all patients with sudden, severe headache with or without associated symptoms.
  • Initial investigation of suspected SAH should be a noncontrast CT scan; most haemorrhages will be apparent on this test.
  • Management of SAH is increasingly becoming endovascular.
  • The outcome for patients with no or only a mild global or focal neurological deficit on presentation has improved, but prehospital mortality and disability from the initial haemorrhage remains a significant problem.
  • Unruptured asymptomatic aneurysms are not an urgent scenario and can be dealt with in consultative outpatient fashion.

    Picture credit: © KO Studios

Headache, a common presentation to primary care physicians, usually has a benign cause and course but can occasionally be a symptom of a neurological condition requiring urgent neurosurgical treatment. ­Secondary headache (headache due to an underlying pathological cause, including structural, vascular, infective, inflammatory or drug-induced) therefore always needs to be considered in patients with new, severe or persistent headache or atypical presentations of headache.1,2

Patients presenting with sudden severe ‘thunderclap’ headache, with or without associated symptoms (which may include nausea and vomiting, loss of consciousness and a focal or global neurological deficit) clearly need immediate investigation with brain CT for probable subarachnoid haemorrhage (SAH) due to a ruptured cerebral aneurysm. However, patients with atypical or mild symptoms of SAH are more difficult to diagnose; these are often the patients with low volume haemorrhages that may not be seen on a CT scan. Further investigations are required in these patients to exclude SAH as the aetiology. As some of these investigations are invasive and involve risk (e.g. lumbar puncture and digital subtraction angiography), significant decisions and recommendations have to be made in patients who often have the mildest headache.2-5

Ruptured cerebral aneurysms have a significantly different natural history to unruptured aneurysms. The re-rupture rate in the first two weeks after haemorrhage is 20% (with mortality of 10%), and in the first six months is 50%.6,7 The annual rupture rate of a small (less than 10 mm) unruptured aneurysm is in the order of 1% per year or less.8


There are, of course, structural causes of headache and ­nontraumatic SAH other than a ruptured cerebral aneurysm, and these are generally discovered on further investigation.9,10 The critical issue is the diagnosis of the haemorrhage itself as a missed haemorrhage can have devastating effects for the patient.11

The investigation and management options for patients with SAH due to a ruptured cerebral aneurysm are discussed in this article, and a case study of a low volume haemorrhage is presented to demonstrate some of the difficulties and complexities surrounding diagnosis (Box and Figures 1a and b). The presentation and management of unruptured cerebral aneurysms is also discussed.


Investigations for SAH

CT scan

A noncontrast CT scan of the brain is the best and most widely available test for the investigation of severe headache.2 It is the most sensitive imaging modality for detecting blood, and will reveal blood in over 95% of patients with SAH, although the sensitivity decreases over time (sensitivity is 98 to 100% in the first 12 hours after SAH, reducing to 93% at 24 hours and to between 57 and 85% six days after SAH).2,12,13