From the Guidelines
A CT scan for a headache is typically needed when there are concerning features suggesting a serious underlying condition, such as a sudden, severe "thunderclap" headache, headache following head trauma, or headache with fever, stiff neck, or rash, as indicated by the Ottawa SAH Rule 1. The decision to perform a CT scan should be made by a healthcare provider after a thorough evaluation, taking into account the patient's age, medical history, and symptoms. Some key factors that may indicate the need for a CT scan include:
- Age ≥40 years
- Neck pain or stiffness
- Witnessed loss of consciousness
- Onset during exertion
- Thunderclap headache (instantly peaking pain)
- Limited neck flexion on examination These criteria are based on the Ottawa SAH Rule, which has been validated in several studies, including a prospective study of 1153 patients, which found the rule to be 100% sensitive and 13.6% specific for identifying patients with subarachnoid hemorrhage 1. High-quality CT scanners can detect subarachnoid hemorrhage with a high sensitivity, especially when the images are interpreted by fellowship-trained, board-certified neuroradiologists 1. The use of CT angiography (CTA) may also be considered, as it has been shown to be a rapid and less invasive alternative to catheter angiography, with sensitivities approaching equivalence to catheter angiography for larger aneurysms 1. However, the decision to perform a CT scan or CTA should be made on a case-by-case basis, taking into account the individual patient's risk factors and symptoms, as well as the potential risks and benefits of the procedure, as noted in the 2012 guidelines for the management of aneurysmal subarachnoid hemorrhage 1.
From the Research
Determining the Need for a CT Scan in Headache Diagnosis
- A CT scan is often required to diagnose the cause of a headache, particularly if it is severe and acute 2, 3, 4, 5.
- The key diagnosis to make in this situation is hemorrhage, either subarachnoid or intraparenchymal, which can be detected by CT scan 2.
- Noncontrast computed tomography is highly sensitive in detecting subarachnoid blood, especially within 6 hours of hemorrhage 3, 5.
- If the CT scan is negative, a lumbar puncture (LP) may be necessary to rule out subarachnoid hemorrhage (SAH), especially if the patient's symptoms are suspicious of SAH 3, 5.
Indications for CT Scan in Headache Diagnosis
- Severe and acute headache 2, 3, 4, 5.
- Suspicion of subarachnoid hemorrhage (SAH) 3, 5.
- Negative neurological examination and no abnormalities at standard CT and CSF analysis 6.
- History of aneurysm or cerebral venous thrombosis (CVT) 6.
Diagnostic Accuracy of CT Scan in Headache Diagnosis
- Noncontrast cranial CT within 6 hours of headache onset accurately rules in and rules out SAH 3.
- CT scan has a high sensitivity and specificity for detecting SAH, especially with fifth generation CT scanners 4.
- CT angiography (CTA) may be necessary to exclude cerebral venous thrombosis (CVT), dissection, or reversible cerebral vasoconstriction syndrome (RCVS) 6.