What are the possible causes of a severe headache in a patient?

Causes of Severe Headache

Severe headaches require immediate evaluation for life-threatening causes including subarachnoid hemorrhage, bacterial meningitis, cerebral venous thrombosis, and intracranial hemorrhage, while also considering primary headache disorders that can present with severe pain. 1, 2

Life-Threatening Causes Requiring Immediate Evaluation

Subarachnoid Hemorrhage (SAH)

• Thunderclap headache (sudden, severe onset reaching maximum intensity within seconds to minutes) is the hallmark presentation and demands immediate non-contrast CT head, which has 95-98% sensitivity within 6 hours of symptom onset. 1, 2, 3
• If CT is negative but clinical suspicion remains high, lumbar puncture is mandatory to detect xanthochromia, which remains 100% sensitive for 2 weeks after hemorrhage and >70% sensitive at 3 weeks. 3
• SAH can present with sentinel headaches (warning leaks) that are frequently misdiagnosed, making any "first or worst" headache a critical red flag. 3
• Aneurysms and arteriovenous malformations are the typical underlying causes, and CTA should be performed immediately if SAH is confirmed on CT to identify the bleeding source. 1

Bacterial Meningitis

• Fever with neck stiffness and severe headache constitutes a medical emergency requiring immediate evaluation and lumbar puncture. 4
• Constitutional symptoms including fever, altered mental status, and meningeal signs (Kernig's sign, Brudzinski's sign) should prompt urgent CSF examination. 1
• Delay in diagnosis can be fatal, making this a cannot-miss diagnosis in any patient with severe headache and fever. 5

Cerebral Venous Thrombosis (CVT)

• Headache is present in nearly 90% of CVT cases and typically progresses over days to weeks, though thunderclap presentation can occur. 1
• Isolated headache without focal neurological findings or papilledema occurs in up to 25% of CVT patients, making this a particularly challenging diagnosis. 1
• Risk factors include oral contraceptive use, pregnancy/postpartum period, infection (especially mastoiditis in children), and hypercoagulable states. 1
• MRI with MR venography is the diagnostic test of choice, with contrast-enhanced MRV helpful for evaluating sigmoid sinuses. 1
• Focal neurological deficits, seizures (present in a significant minority), and signs of increased intracranial pressure may accompany the headache. 1

Intracranial Hemorrhage and Mass Lesions

• Brain tumors present with headache accompanied by abnormal neurologic findings in 94% of cases, with 60% having papilledema at diagnosis. 1
• Additional neurologic signs include gait disturbance, abnormal reflexes, cranial nerve findings, and altered sensation—making meticulous neurologic examination essential. 1
• MRI with and without contrast is the imaging modality of choice when tumor or mass lesion is suspected. 1
• Arterial dissection (carotid or vertebral) should be suspected with sudden severe unilateral headache, especially when associated with Horner syndrome or other focal neurologic signs. 1

Secondary Causes Requiring Urgent Evaluation

Pseudotumor Cerebri (Idiopathic Intracranial Hypertension)

• Presents with severe headaches, visual impairments, and papilledema, typically in overweight females of childbearing age but can occur in males and prepubertal children. 1
• MRI with and without contrast should demonstrate secondary signs including empty sella, dilated optic sheaths, tortuous or enhancing optic nerves, and flattening of posterior globes. 1
• Normal brain parenchyma without hydrocephalus, mass, or structural lesion distinguishes this from other causes of increased intracranial pressure. 1
• MR venography is indicated to evaluate for venous sinus abnormalities, found in 52% of cases. 1

Temporal Arteritis (Giant Cell Arteritis)

• Must be excluded in all patients over age 50 with new-onset severe or recurrent headaches. 3, 6
• Headache is the most common symptom, reported by 60-90% of patients, though ESR can be normal in 10-36% of cases. 3
• Temporal artery biopsy can give false-negative results in 5-44% of patients, so clinical suspicion must remain high. 3
• Visual loss can occur rapidly if untreated, making this a time-sensitive diagnosis. 3

Spontaneous Intracranial Hypotension (SIH)

• Orthostatic headache affecting the whole head that worsens within 2 hours of becoming upright and improves >50% within 2 hours of lying flat is highly characteristic. 4
• A descending distribution from head to nape and downward is pathognomonic and should never be dismissed as benign. 4
• Associated symptoms include neck pain, nausea, tinnitus, hearing changes, and photophobia. 4
• Urgent neurology referral within 2-4 weeks if self-caring, within 48 hours if requiring help, with patients advised to lie flat pending evaluation. 4

Primary Headache Disorders Presenting with Severe Pain

Migraine

• Can present with severe, bilateral whole-head pain (not always unilateral), with throbbing quality, moderate-severe intensity, and worsening with routine activity. 4, 7
• Must have at least two of: unilateral location, throbbing character, worsening with activity, or moderate-severe intensity, plus nausea/vomiting and/or photophobia/phonophobia. 7
• Affects 18% of women and 6.5% of men in the United States. 7
• Patients typically prefer to lie still in a dark, quiet room, distinguishing it from cluster headache. 8

Cluster Headache

• Strictly unilateral, severe to very severe pain lasting 15-180 minutes, with frequency of 1-8 attacks per day. 8, 7
• Accompanied by ipsilateral cranial autonomic symptoms (lacrimation, conjunctival injection, nasal congestion, ptosis, miosis). 8
• Patients characteristically pace or rock during attacks, contrasting with migraine patients who remain still. 8
• Affects approximately 0.1% of the general population. 7

Tension-Type Headache

• Bilateral pressing/tightening quality, mild to moderate intensity, not aggravated by routine activity. 4, 7
• Lacks prominent associated symptoms (no nausea, photophobia, or autonomic features). 7
• While typically not severe, can occasionally present with significant pain intensity. 4

Critical Red Flags Requiring Immediate Neuroimaging

• Thunderclap onset (sudden severe headache reaching maximum intensity rapidly) 4, 2
• Focal neurological signs or symptoms (weakness, sensory changes, visual field defects, aphasia) 4, 9
• Unexplained fever with headache 9
• Recent head or neck trauma 9
• New headache in patient over age 50 9, 3
• Rapidly increasing headache frequency or severity 9
• Headache awakening patient from sleep (less worrisome but warrants evaluation) 9
• Headache brought on by Valsalva maneuver, cough, or exertion 9
• History of cancer or immunosuppression (HIV infection) 9
• Pregnancy 9
• Abnormal neurological examination (39% positive predictive value for intracranial pathology) 2

Diagnostic Approach Algorithm

Immediate Evaluation (Emergency Department)

• Non-contrast CT head is first-line for thunderclap headache, trauma, or suspected acute hemorrhage due to availability and high sensitivity (95-98% for SAH within 6 hours). 1, 2
• Lumbar puncture if CT negative but SAH suspected, or if meningitis suspected with fever and neck stiffness. 2, 4
• MRI brain is preferred over CT for most other indications when patient is stable, as it provides superior detail without radiation. 1, 9

Urgent Outpatient Evaluation

• MRI with and without contrast for suspected tumor, pseudotumor cerebri, or when red flags present without acute emergency features. 1
• MR venography for suspected cerebral venous thrombosis or pseudotumor cerebri. 1
• Temporal artery biopsy and ESR for suspected temporal arteritis in patients over 50. 3

Routine Evaluation

• Neuroimaging is NOT routinely indicated for typical primary headaches without red flags. 7
• The yield of neuroimaging in patients with headache and normal neurologic examination is quite low: brain tumors 0.8%, AVMs 0.2%, aneurysms 0.1%. 3
• For migraine specifically, the yield is even lower: brain tumor 0.3%, AVM 0.07%, aneurysm 0.07%. 3

Common Pitfalls to Avoid

• Do not dismiss orthostatic headache with descending pattern as benign—this is characteristic of spontaneous intracranial hypotension requiring specific evaluation. 4
• Do not attribute "sinus headache" to sinusitis—most patients with self-diagnosed sinus headache actually have migraine or tension-type headache. 4
• Do not miss medication overuse headache—overuse of acute medications (≥10 days/month) can transform episodic headache into chronic daily headache. 4, 10
• Do not rely solely on ESR to exclude temporal arteritis—it can be normal in 10-36% of cases. 3
• Do not assume bilateral headache excludes serious pathology—many secondary causes present with diffuse pain. 4
• Do not perform lumbar puncture before neuroimaging if increased intracranial pressure suspected—risk of herniation. 1
• Do not miss the 25% of CVT patients who present with isolated headache—maintain high suspicion in patients with risk factors. 1
• Do not assume normal CT excludes SAH after 6 hours—sensitivity drops to 74% by day 3 and 50% by 1 week. 3