<prompt> A 55yers old male has sudden onset of thunder clap headache following by loss of consiusness for 4 hour investigation isNon contrast ct followed by angiogramPETMRI angiogramContrast enhanced CT  <response>: A MRI angiogram 128- H 18th Brad- Lee Neurology 5thPrimary thunderclap headache Sudden onset of severe headache may occur in the absence of any known provocation DD-i Sentinel bleed of an intracranial aneurysmii Cervicocephalic arterial dissectioniii Cerebral venous thrombosisiv Sympathomimetic drugs or tyramine containing foods in patients who is taking MAO is or they may be a symptom of pheochromocytoma. First presentation of any sudden onset severe headache should be vigoruously investigated with neuroimaging CT or when possible MRI with MR angiography and CSF examination Nimodipine may be helpful. Although by definition the vasoconstriction of primary thunder clap headache resolves spontaneously.Red flag svmptons in headache 1157- Dividson 22ndSymptomsPossible explanationSudden onset Maximal immediately or with in minutes- Subarachnoid haemorrhage- CCA- Pituitary apoplexy- MeningitisFocal neurological symptoms other than for typically migrainousIntracranial mass lesionsVascularNeoplasticInfectionsConstitutional symptoms Weight loss General malaise Pyrexia Meningism Rash Meningoencephalitis Neoplastic lymphoma or metastasis Inflammatory vasculiticRaised intracranial pressure worse on wakeninglying down, associated VomitingIntracranial mass lesionsNew onset aged 60 yearsTemporal arteritis Thunderclap headache is an acute and servre headache that is maximum in intensity at onset and has been likened to a clap thunder. The term TCH was initially used by Day and Raskin in reference to the pain associated with an unruptured intracranial aneurysm. However, multiple cause of thunderclap headache have since been describedsubarachnoid hemorrhage is the most common cause of thunderclapQ.Primary Thunder Clap headache Primary TCH is diagnosed when all other potential underlying cause have been eliminated by diagnostic testing Primary TCHs can recur intermittently and are generally associated with benign outcomeThe international Headache societys diagnostic criteria for primary TCHA. Severe headpain fulfilling criteria B and CB. Both of the following characteristics- Sudden onset,- Reaching maximum intensity in 1 min lasting form 1 hour to 10 daysC. Does not recur regularly over subsequent weeks or months.D. Not attributed to another disorder normal cerebrospinal fluid and normal brain imaging are neededSecondary causes of Thunderclap headache- Subarachnoid hemorrhage0- Sentinel headache- Cerebral venous sinus thrombosis0- Cervical artery dissection- Spontaneous intracranial hypotension- Pituitary apoplexy0- Retroclival hematoma- Ischaemic stroke- Acute hypertensive crisis- Reversible cerebral vasoconstriction syndrome- Third ventricle colloid cyst- Intracranial infection- Priamary thunderclap headache- Primary cough, sexual and exertional headache 