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A simple non contrast CT is invaluable in showing structural anatomy and helps immediately separate those who need neurosurgery from those who don't. CT Contrast if available can be helpful to help highlight tumours. For those with Thunderclap headache and normal CT and LP the prognosis is very good.

Assessing Acute Severe Headache

ABC, IV access get CT head and get help from ITU if airways or low GCS IV fluids. Simple analgesia Paracetamol/Codeine first until diagnosis clearer Abnormal CT: SAH or Haemorrhage or Hydrocephalus or Mass or Abscess : Assess by neurosurgeons Acute Ischaemic Stroke: Dissection, RCVS, Cerebral venous thrombosis - treat as indicated Acute Infection: Consider LP and Aciclovir/Cefotaxime Thunderclap headache but CT normal: consider LP at 12 hours exclude small SAH

New severe headache/Thunderclap

• Sudden-onset severe headache reaching maximum intensity within 5 minutes may indicate serious causes such as
  • Subarachnoid haemorrhage
  • Intracranial haemorrhage
  • Venous sinus thrombosis
  • Reversible vasoconstriction syndrome
  • Hypertensive encephalopathy
  • Carotid/vertebral artery dissection.
  • Bacterial meningitis
  • Pituitary apoplexy
  • Low pressure headache
  • First ever migraine/cluster headache
• New onset headache in a person aged over 50 years consider as well
  • Giant cell arteritis
  • Space occupying lesion.
  • Glaucoma
• Progressive Headache esp worse in morning or with cough or straining
  • Tumour
  • Subdural haematoma
  • Any SOL
  • Hydrocephalus
  • Arnold-Chiari malformation
  • Posterior fossa disease
• Fever, neck pain, photophobia
  • Bacterial Meningitis
  • Viral meningitis
  • Systemic illness
• Fever, neck pain, photophobia + focal neurology/seizure
  • HSV Encephalitis
  • Meningoencephalitis
  • ADEM
• Headache and papilloedema
  • Space occupying lesions
  • Cerebral venous sinus thrombosis
  • Benign intracranial hypertension.
• New-onset neurological deficit, change in personality and new-onset cognitive dysfunction - consider serious causes such as a cerebrovascular event, malignancy or other space occupying lesions such as subacute or chronic subdural hematoma.
• Atypical aura (duration greater than 1 hour, or including motor weakness) or aura occurring for the first time in a patient during use of combined oral contraceptives - consider serious causes such as cerebrovascular event.
• Dizziness - consider serious causes such as ischaemic or haemorrhagic stroke.
• Visual disturbance - can be associated with migraine but also with serious causes such as acute closure glaucoma and temporal arteritis.
• Vomiting - can associated with migraine but may also be associated with a serious cause of headache such as mass lesion, brain abscess, or carbon monoxide poisoning. Carbon monoxide poisoning if household contacts have similar symptoms.

Precipitating factors such as

• Preceding recent (usually within the past 3 months) head trauma - consider serious causes such as subacute or chronic subdural hematoma.
• Headache triggered by a Valsalva manoeuvre (such as coughing, sneezing, bending or exertion [physical or sexual]) - consider serious causes such as Chiari 1 malformation or a posterior fossa lesion.
• Headache that worsens on standing - consider a CSF leak.
• Headache that worsens on lying down - consider a space-occupying lesion or cerebral venous sinus thrombosis.

Comorbidities such as:

• Compromised immunity (for example due to HIV or immunosuppressive drugs) - consider serious causes such as cerebral infection or malignancy.
• Current or past malignancy - consider serious causes such as cerebral metastases.
• Current or recent pregnancy - consider serious causes such as pre-eclampsia.

References

• Headache assessment NICE UK guidance
• Thunderclap* is usually worst ever headache, Onset to full severity within seconds, May be associated with syncope
• Priorities must be assessed with attention to the seriousness so that SAH, CVT, Stroke and Meningitis and pituitary apoplexy or even CO toxicity need to be considered and excluded first of all.

Causes	Details	Seriousness
Acute Stroke	Ischaemic and acute haemorrhagic stroke can cause sudden headache but more common with haemorrhage. CT scan will be diagnostic for haemorrhage. Particularly worrying is patient on anticoagulation or with any focal neurology. In those with Ischaemic stroke, it is often on the affected side and is a vascular headache that represents shunted blood through collaterals due to a major arterial obstruction, e.g. MCA occlusion. Needs an urgent CT head. In stroke Headache commoner: Haemorrhagic > Ischaemic, Posterior > Anterior circulation infarcts, Thrombotic > embolic ischaemic strokes, Cortical > deep white matter strokes, Venous > arterial infarction. In practice, a CT head is always needed	Life/Disability threatening
Subarachnoid Haemorrhage	red flags worst ever headache, neck stiffness, meningism, vomited, onset with exercise. Rupture of an aneurysm or AVM is usually catastrophic and presents with thunderclap headache and often collapse and coma	Life / disability threatening
Cerebral Venous thrombosis	consider this within the differential of thunderclap presentation. CT head may be normal, show clot or venous infarction +/- haemorrhage. Suspect if LP shows high red cells, high opening pressure and increased lymphocytes. Diagnose formally with CT venography or MR venography, whichever available. Anticoagulate.	Life / disability threatening
Cervical Dissection	Neck, retro-orbital pain or occipital pain. Associated focal neurological signs. Horner's syndrome with ipsilateral carotid dissection. Brainstem signs with vertebral dissection and may also have a Horner's from PICA thrombosis and lateral medullary syndrome.	Life/disability threatening
Reversible Vasconstriction syndrome	Reversible cerebral vasoconstriction syndrome (RCVS): single or repeated severe, often bilateral thunderclap headaches. Seizures and focal neurological deficits, ischaemic stroke and non-aneurysmal SAH, LP blood and protein. MRA/CTA/DSA: beads on a string appearance of cerebral arteries which resolves at 3 months. Verapamil/Nimodipine may be given. Multiple suggested causes idiopathic, pregnancy, vasoactive drugs, hypertensive crisis, etc.	Not Life threatening
Pituitary Apoplexy	severe headache and IIIrd nerve palsy and visual loss as severe pressure around optic nerve from haematoma. CT/MRI + contrast may show infarction/bleeding. May have known pituitary tumour. Needs neurosurgical decompression if vision affected. Needs IV Hydrocortisone because acute hypopituitarism is possible. Neurosurgical consult	Potentially Life/vision threatening
Acute CNS infection	bacterial meningitis: look for petechiae if meningococcaemia, neck stiffness, Kernig's sign, meningism. Acute delirium in elderly, pyrexia. Treat empirically if any suspicion. Many with a fever of recent onset and headache will have a systemic illness headache. This is poorly understood. Usually self-limiting with a good outcome, when the underlying infection resolves. Some, however, end up with a non-specific persistent headache for months.	Life threatening/disabling
Temporal (giant cell) arteritis	subacute headache in older patient. Check ESR or CRP. Temporal artery tenderness or polymyalgia symptoms or transient or persistent visual loss. Needs TAB.	Vision/stroke threatening
Acute angle closure glaucoma	consider in a patient with headache associated with a red eye, halos or unilateral visual symptoms. Urgent ophthalmology referral.	Vision threatening
Carbon monoxide poisoning	CO produced when gas, oil, coal or wood do not burn fully. Cold weather. More than one person affected in shared accommodation. Check ABG and COHb levels. SaO2 falsely normal	Life threatening
Spontaneous intracranial hypotension	marked low pressure headache on standing. Can come on suddenly. Relieved by remaining supine. Post LP or spontaneous leak. Give fluids and simple caffeinated drinks. May need epidural blood patches (usually done by anaesthetist). Typical meningeal enhancement on MRI and cerebellar tonsillar descent and bilateral SDH. CSF opening pressure <10 cmH2O.	Not Life threatening
Migraine (no aura)	aura absent but severe often pulsating, often recurring unilateral headache may last 4-72 h. Shorter with effective treatment, longer than 72 h in others. Desire to be alone, quiet, lie down and sleep. The severe attack looks ill, nauseated, grey pallor. Feels very miserable. Headache is often worse than those with aura. Manage as migraine with aura.	Low risk of harm
Migraine with aura	recurrent episodic headache with systemic symptoms. Comes on gradually, and there may be preceding aura such as tingling, weakness, and altered speech, word-finding difficulties, flashing lights, scotomas or fortification spectra. Positive family history. Headache then comes on and lasts 4-72 h by definition but some are shorter and some longer. Patients feel awful; look grey, usual response for severe attacks is to want to lie down and sleep. First line: Aspirin 900 mg or IBUPROFEN 600 mg PO if not vomiting or else DICLOFENAC 100 mg PR + METOCLOPRAMIDE. Second line: triptans, e.g. SUMATRIPTAN 50 mg PO or 6 mg SC (C/I with IHD/TIA, stroke). If severe vomiting, consider IV NS.	Low risk of harm
Cluster headaches	(commonest of the trigeminal autonomic cephalgias). Occur in repeated attacks. Severe. Unilateral. Retro-orbital stabbing. Tearing, miosis, ptosis. Restless patient pacing floor. Give 100% O2 and SUMATRIPTAN 6 mg SC as the first choice treatment for the relief of acute attacks of cluster headache. Prevent with PREDNISOLONE or VERAPAMIL. Commoner in men.	Benign
Paroxysmal hemicranias	severe, unilateral orbital, supraorbital, and/or temporal pain, always same side, lasting 2-45 min up to 5-10 times/day. With either conjunctival injection, lacrimation, nasal congestion, runny nose, ptosis, eyelid oedema. Dramatic effect of INDOMETHACIN 150 mg daily.	Benign
Short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT) syndrome	rare, males > females in middle age. Moderate headache lasts 1 minute. Ipsilateral conjunctival injection, lacrimation. Nasal stuffiness/rhinorrhoea and increased intraocular pressure on the symptomatic side and swelling of the eyelids. Usually frontal and periocular. Intractable to medications.	Benign
Medication overuse headache	must be excluded in all patients with chronic daily headache (headache >15 days per month for more than 3 m) and those using opioid-containing medications or overusing triptans are at most risk. Resembles migraine or tension type headache. Chronic analgesic ingestion especially codeine. Gradual withdrawal. Prevent with AMITRIPTYLINE or GABAPENTIN.	Benign
Tension headache	usually a chronic band-like headache but many variants. Rarely truly thunderclap. Often long history of similar episodes. No associated symptoms or signs beyond headache. Give NSAID or paracetamol.	Benign
Coital/post-coital headache	diagnosis once SAH excluded. May be experienced with orgasm. There is a real possibility that this could be SAH but it would be less likely if it has occurred several times before without incident. In future take NSAIDs prior to sex. Exclude SAH in all new cases with LP/CT. Benign form is orgasmic cephalgia once SAH safely excluded.	Benign
Exploding head syndrome	not a true headache but can be misunderstood with poor history. Auditory hallucination that occurs whilst falling asleep sound like a gun going off in ones head. May be unable to speak or move. Benign condition avoid extensive investigations or treatment	Benign

Investigations

• FBC, U&E, ESR if Temporal arteritis suspected
• CT Brain must be performed earlier and will exclude many causes. If done within 6 hrs of onset newer scanners basically can exclude SAH
• CT / CTV or MRI / MRV if Cerebral venous sinus thrombosis suspected
• CTA if RCVS suspected or with SAH in the acute setting to help localise any aneurysm
• Immediate LP and CSF with measurement of opening pressure: if encephalitis or meningitis or Idiopathic intracranial hypertension
• Delayed LP and CSF or a late SAH presentation suspected. If looking for SAH then delay until 12h. Ensure experienced operator. Also, measure pressure. Send 4th bottle for xanthochromia which is best performed using CSF spectrophotometry. Protect sample from light wrapped in foil and get to the lab quickly

Patients who have had thunderclap headache who have a normal CT Brain and normal CSF carry an excellent long-term prognosis

Management

• ABC as ever. If comatose and unwell then once stable with intubation and ventilation if needed and then urgent CT head usually will help to define the cause and urgent need.
• If stable more time can be taken to dwell on the history and exam and need for urgent CT(A/V) and CSF sampling.

References and further reading

• Acute Headache. Ulster Med J. 2014 Jan; 83(1): 3-9. Raeburn B Forbes
• Dr Ben Wakerley Consultant Neurologist Gloucestershire Royal Hospital. Acute headache on the AMU