# Secondary Headache Red Flags and Emergencies

## Introduction

While most headaches are primary disorders, secondary headaches caused by life-threatening conditions demand rapid recognition. The neurologist must systematically identify red flags that warrant urgent investigation. This lecture reviews the "SNOOP" mnemonic and major secondary headache emergencies.

## The SNOOP Red Flag Mnemonic

| Letter | Red Flag | Examples / Concerns |
|---|---|---|
| **S** | Systemic symptoms or disease | Fever, weight loss, cancer, HIV, pregnancy |
| **N** | Neurological signs | Papilledema, focal deficits, altered mental status, seizures |
| **O** | Onset sudden | Thunderclap (max in <1 min) → SAH, RCVS, CVST |
| **O** | Older age (>50) | Giant cell arteritis, mass lesion, subdural |
| **P** | Pattern change | Progressive worsening, positional, Valsalva-triggered, new type |

The SNOOP framework organizes headache red flags into five categories. "S" stands for systemic symptoms (fever, weight loss, cancer, HIV, pregnancy) or systemic disease. "N" denotes neurological symptoms or signs including papilledema, focal deficits, altered mental status, and seizures. The first "O" indicates onset that is sudden, particularly thunderclap headache reaching maximal intensity in less than 1 minute. The second "O" refers to older age at onset, specifically new headache after age 50. "P" indicates a pattern change: progressive worsening, positional headache, Valsalva-triggered headache, or headache fundamentally different from prior ones.

## Thunderclap Headache

### Definition and Differential Diagnosis

Thunderclap headache is defined as headache reaching maximum intensity within 1 minute, often described as the "worst headache of my life." Subarachnoid hemorrhage (SAH) must be excluded first. Other causes include reversible cerebral vasoconstriction syndrome (RCVS), cerebral venous sinus thrombosis (CVST), cervical artery dissection, pituitary apoplexy, spontaneous intracranial hypotension, and meningitis.

### Subarachnoid Hemorrhage

Non-contrast CT head has a sensitivity exceeding 95% within 6 hours, decreasing to approximately 85% by 24 hours and 50% by 5 days. If CT is negative, lumbar puncture must be performed looking for xanthochromia (spectrophotometry preferred) and an elevated RBC count that does not clear between tubes. CT angiography identifies the causative aneurysm if SAH is confirmed. A sentinel headache (warning leak) precedes major SAH in approximately 30% of cases.

### Reversible Cerebral Vasoconstriction Syndrome

RCVS presents with recurrent thunderclap headaches over 1-4 weeks, often triggered by vasoactive substances (triptans, SSRIs, cannabis, cocaine) or the postpartum state. CT/MRI may show convexity SAH, posterior reversible encephalopathy, or infarction. Angiography demonstrates segmental vasoconstriction that resolves within 12 weeks. CSF is normal, which distinguishes RCVS from PACNS. Treatment involves removing the offending agent, verapamil or nimodipine, and supportive care.

## Cerebral Venous Sinus Thrombosis

Headache occurs in 90% of CVST cases and may be thunderclap, progressive, or positional. Risk factors include oral contraceptives, pregnancy or puerperium, prothrombotic states, infection, and dehydration. Associated features include seizures, focal deficits, papilledema, and altered consciousness. Diagnosis requires CT venography or MR venography; non-contrast CT alone is insufficient. Treatment is anticoagulation with heparin (even in the presence of hemorrhagic infarction), followed by warfarin or a DOAC for 3-12 months.

## Cervical Artery Dissection

Carotid or vertebral artery dissection causes unilateral head, neck, or face pain with or without ischemic symptoms. Carotid dissection produces unilateral frontal or periorbital headache, Horner syndrome (miosis, ptosis, anhidrosis), and ipsilateral cranial nerve palsies (CN XII most common). Vertebral dissection causes occipital or posterior neck pain and may lead to lateral medullary or cerebellar infarction. Dissection may follow minor trauma, chiropractic manipulation, or occur spontaneously. Diagnosis is made with CTA or MRA of the head and neck; fat-saturated T1 MRI shows intramural hematoma. Treatment is antithrombotic therapy (the CADISS trial showed no significant difference between anticoagulation and antiplatelet therapy).

## Giant Cell Arteritis

New headache in a patient over 50 years old must raise consideration of giant cell arteritis (GCA). The headache is temporal and boring, accompanied by scalp tenderness, jaw claudication, and visual symptoms. Anterior ischemic optic neuropathy is the most feared complication and can cause permanent blindness. ESR and CRP are markedly elevated (ESR above 50 mm/hr, CRP above 2.5 mg/dL). Temporal artery biopsy is the gold standard; skip lesions require an adequate specimen length of 2 cm or more. Temporal artery ultrasound showing the halo sign has high specificity. Treatment is immediate high-dose prednisone (1 mg/kg/day) without waiting for biopsy results; IV methylprednisolone should be given if visual loss is present. Tocilizumab serves as a steroid-sparing agent (GiACTA trial).

## Idiopathic Intracranial Hypertension

The classic presentation is headache with papilledema in a young obese woman. Symptoms include daily headache worsened by Valsalva, transient visual obscurations, pulsatile tinnitus, and diplopia from CN VI palsy. Diagnosis requires elevated opening pressure above 25 cm H2O on lumbar puncture with normal CSF composition, and MRI showing empty sella, optic nerve sheath distension, and transverse sinus stenosis. Treatment consists of weight loss and acetazolamide (IIHTT trial); fulminant cases require CSF diversion (optic nerve sheath fenestration or VP shunt).

## Spontaneous Intracranial Hypotension

The hallmark is orthostatic headache that worsens within minutes of standing and improves with recumbency. It is caused by a CSF leak from a dural tear, often in the thoracic spine. Brain MRI shows diffuse pachymeningeal enhancement, brain sagging, subdural collections, and pituitary engorgement. Spine MRI or CT myelography identifies the leak site. Treatment includes bedrest, hydration, and caffeine, with epidural blood patch as the first-line definitive therapy. Targeted fibrin glue patch or surgery is used for refractory cases.

## Pituitary Apoplexy

Pituitary apoplexy causes sudden severe headache from hemorrhage or infarction of a pituitary adenoma. Associated features include visual field deficits (bitemporal hemianopia), ophthalmoplegia from cavernous sinus compression, altered consciousness, and acute adrenal insufficiency. CT may show sellar hemorrhage, but MRI with pituitary protocol is more sensitive. Emergency management requires IV hydrocortisone (adrenal crisis can be fatal) and urgent neurosurgical consultation.

## Clinical Pearls

Every thunderclap headache is SAH until proven otherwise; if CT is negative, lumbar puncture is mandatory. Normal CSF in the setting of thunderclap headache with angiographic vasoconstriction points to RCVS, not PACNS. In any patient over 50 years with new headache, ESR and CRP should be checked and the patient examined for scalp tenderness and jaw claudication. Orthostatic headache with pachymeningeal enhancement is spontaneous intracranial hypotension, not meningitis.

## References
- Dodick DW. Pearls: headache. Semin Neurol. 2010;30(1):74-81.
- Ducros A, Wolff V. The typical thunderclap headache of reversible cerebral vasoconstriction syndrome and its various triggers. Headache. 2016;56(4):657-673.
- Saposnik G, Barinagarrementeria F, Brown RD Jr, et al. Diagnosis and management of cerebral venous thrombosis: a statement for healthcare professionals from the American Heart Association/American Stroke Association. Stroke. 2011;42(4):1158-1192.
- Stone JH, Tuckwell K, Dimonaco S, et al. Trial of tocilizumab in giant-cell arteritis. N Engl J Med. 2017;377(4):317-328.