What causes sharp headaches?

Causes of Sharp Headaches

Sharp headaches have diverse etiologies ranging from benign primary headache disorders to life-threatening vascular and infectious conditions, with the clinical context—particularly sudden onset ("thunderclap"), associated symptoms, and patient demographics—determining the urgency of evaluation and likelihood of serious pathology.

Primary Headache Disorders

Sharp or stabbing pain can occur in several primary headache syndromes:

• Migraine can present with sharp, severe pain that is typically unilateral, pulsatile, and moderate to severe in intensity, worsening with routine physical activity 1, 2. The pain must have at least two of these characteristics: unilateral location, throbbing character, worsening with activity, or moderate-to-severe intensity 1.

• Cluster headache produces strictly unilateral, severe to very severe sharp pain lasting 15-180 minutes, occurring 1-8 times daily, accompanied by ipsilateral autonomic symptoms including lacrimation, nasal congestion, and ptosis 3, 1. This affects approximately 0.1% of the population 1.

• Tension-type headache typically causes bilateral pressing or tightening pain rather than sharp pain, is mild to moderate in severity, and lacks prominent associated symptoms 3, 1. This is the most common primary headache, affecting 38% of the population 2.

Life-Threatening Secondary Causes

Sudden-onset severe sharp headache ("thunderclap") requires immediate evaluation for potentially fatal conditions:

Subarachnoid Hemorrhage (SAH)

• The "worst headache of my life" with sudden onset strongly suggests SAH from ruptured aneurysm 4, 5. One case series described a 20-year-old woman with the worst headache she ever experienced due to subarachnoid hemorrhage 5.

• Non-contrast CT has 95% sensitivity on day 0, declining to 74% by day 3,50% at 1 week, and nearly nil by 3 weeks 6. If CT is negative but suspicion remains high, lumbar puncture showing xanthochromia has 100% sensitivity from 12 hours through 2 weeks post-hemorrhage 6.

• Intracerebral hemorrhage is more common with ruptured mycotic aneurysms, whereas acute subarachnoid hemorrhage occurs more commonly with ruptured congenital berry aneurysms 4.

Intracranial Mycotic Aneurysms (ICMA)

• Severe, localized, unremitting headache, often with homonymous hemianopsia, indicates ICMA with impending rupture in patients with infective endocarditis 4. ICMAs occur in 2-10% of endocarditis cases 4.

• Sudden onset of intracranial hemorrhage with severe headache, rapid mental status deterioration, and loss of consciousness suggests ruptured mycotic aneurysm in the middle cerebral artery circulation 4. The mean time from endocarditis diagnosis to hemorrhage is 18 days 4.

Arterial Dissection

• Sudden severe unilateral sharp headache with Horner syndrome suggests carotid or vertebral artery dissection 4. MRI is more sensitive than CT for detecting acute infarction from dissection 4.

Venous Sinus Thrombosis

• Sharp headache with intracranial extension of infection (particularly mastoiditis) or in girls using oral contraceptives raises concern for venous sinus thrombosis 4. MRV is the diagnostic modality of choice 4.

Other Secondary Causes Requiring Investigation

Spontaneous Intracranial Hypotension (SIH)

• Sharp headache that is absent or mild (1-3/10) on waking, develops within 2 hours of becoming upright, and improves >50% within 2 hours of lying flat suggests SIH 4. Thunderclap headache followed by orthostatic headache is a recognized presentation 4.

Infectious Causes

• Severe headache with fever in patients with infective endocarditis may indicate intracranial mycotic aneurysm, occurring in 55-77% of cases in the middle cerebral artery 4. The first case example described a 41-year-old with severe headaches due to cryptococcal meningitis 5.

Mass Lesions

• Headache with recent change in character, particularly if constant and sleep-disturbing, warrants evaluation for tumor 5. One case involved a young woman whose headaches assumed a different character due to a large parietal meningioma 5.

• Headache with transient diplopia and projectile vomiting suggests posterior fossa mass, as illustrated by a case of ependymoma 5.

Red Flags Requiring Urgent Investigation

The following features mandate neuroimaging or other urgent evaluation 1, 2, 7, 8:

• Thunderclap onset (sudden, severe, "worst ever")
• Focal neurologic signs or symptoms
• Papilledema or neck stiffness
• Unexplained fever
• Age ≥50 years with new-onset headache
• History of cancer or immunosuppression
• Headache awakening patient from sleep
• Headache provoked by Valsalva maneuver, cough, or exertion
• Rapidly increasing headache frequency
• Personality changes or altered mental status
• Recent head or neck trauma

Diagnostic Approach

• Non-contrast CT is the initial test for suspected acute SAH, with 98% sensitivity and 99% specificity 4. MRI with FLAIR and susceptibility-weighted sequences improves detection of subacute SAH 4.

• MRI is preferred over CT for most other secondary headache evaluations when red flags are present 1, 7. Routine neuroimaging is NOT indicated for typical primary headaches without concerning features 3, 1.

• CTA or MRA should follow positive CT when SAH is identified to evaluate for aneurysm 4. Conventional arteriography may be needed for small vessel disease or when non-invasive imaging is unclear 4.

Critical Pitfalls

• Sentinel headaches from small aneurysmal leaks are frequently misdiagnosed as migraine or tension-type headache 6, 5. Maintain high suspicion for SAH in any "first or worst" headache presentation.

• Up to 15% of patients ≥65 years with new-onset headache have serious pathology including stroke, temporal arteritis, neoplasm, or subdural hematoma 6. The erythrocyte sedimentation rate can be normal in 10-36% of temporal arteritis cases 6.

• Subdural hematomas can present with nonspecific headache patterns 6. Consider imaging in patients with mild head injury and persistent headache, as 1-3% have life-threatening pathology 6.