# Subarachnoid Haemorrhage > Subarachnoid haemorrhage for NEET-PG Medicine: thunderclap headache, CT then lumbar puncture, Hunt-Hess grading, nimodipine and delayed vasospasm. - Canonical URL: https://prepelephant.com/topics/neet-pg/medicine/subarachnoid-haemorrhage - Exam / course: NEET-PG · Subject: Medicine - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-08 - Last updated: 2026-10-08 - Reference basis: Harrison's Principles of Internal Medicine; Adams and Victor's Principles of Neurology; Davidson's Principles and Practice of Medicine - How to cite: "Subarachnoid Haemorrhage", PrepElephant, https://prepelephant.com/topics/neet-pg/medicine/subarachnoid-haemorrhage ## Direct answer Subarachnoid haemorrhage is bleeding into the subarachnoid space, most often from a ruptured saccular aneurysm at the Circle of Willis, producing a thunderclap headache that peaks within a minute. Non-contrast CT within six hours of onset is the first test, lumbar puncture for xanthochromia follows a negative scan, and CT or digital subtraction angiography then defines the aneurysm. ## What you must remember - **Thunderclap headache:** maximal intensity within a minute, often with neck stiffness, vomiting, photophobia and sometimes transient loss of consciousness. - **Imaging window:** non-contrast CT within six hours of onset on a modern scanner detects most cases, but a negative late scan does not exclude the diagnosis. - **Lumbar puncture:** xanthochromia from bilirubin is looked for after about twelve hours; red cells that do not clear across successive tubes suggest bleeding, though a traumatic tap can confuse. - **Hunt-Hess grades:** I, asymptomatic or mild headache; II, moderate to severe headache with neck stiffness and no focal deficit beyond cranial nerve palsy; III, drowsiness with mild focal deficit; IV, stupor with hemiparesis; V, coma. - **Fisher grade:** thicker subarachnoid clot on CT predicts higher vasospasm risk, which peaks in the second week. - **Nimodipine:** 60 mg every four hours for 21 days improves neurological outcome, probably through protection against ischaemia rather than by preventing vasospasm itself. - **Aneurysm securing:** clipping or endovascular coiling, ideally early, prevents rebleeding, a major early threat; blood pressure is controlled until then. - **Delayed ischaemia:** monitored clinically and with transcranial Doppler, treated with euvolaemia and induced hypertension, with rescue angioplasty for refractory vasospasm. ## Worked example: a sudden headache at a desk A 41-year-old woman collapses at her desk with a headache that reaches peak intensity in seconds, then vomits. On arrival she is alert, with neck stiffness and no focal deficit, which places her in Hunt-Hess grade II. 1. **Image the head:** Non-contrast CT shows thick subarachnoid blood with intraventricular extension, a pattern that carries high vasospasm risk. CT angiography identifies an anterior communicating artery aneurysm, and she goes to neurocritical care. 2. **Start nimodipine and secure:** Nimodipine is started at 60 mg every four hours. The aneurysm is secured early by coiling or clipping according to local expertise, with blood pressure controlled until then. 3. **Monitor sodium:** Sodium is monitored closely, because hyponatraemia after subarachnoid haemorrhage may reflect cerebral salt wasting, which needs saline, rather than SIADH, which needs fluid restriction. Treating the wrong problem can worsen her. 4. **Watch for delayed ischaemia:** From about day four to fourteen the risk of delayed ischaemia rises, so transcranial Doppler and neurological checks are repeated. 5. **Treat new deficits:** If new deficits appear, euvolaemia and induced hypertension are used, and rescue angioplasty is considered for refractory vasospasm. 6. **Judge the outcome:** The outcome depends on early securing and vigilant monitoring rather than any single drug. ## Where the exam sets its traps Four traps recur in examiner questions. - **Trap:** treating a normal CT as the end of the question — **Correct:** a negative scan done after six hours is not reassuring when suspicion stays high, so lumbar puncture for xanthochromia follows. Reversible cerebral vasoconstriction syndrome, cerebral venous thrombosis, dissection and pituitary apoplexy can all mimic thunderclap headache. - **Trap:** saying nimodipine prevents angiographic vasospasm — **Correct:** it is given for outcome rather than to prevent angiographic vasospasm, a point candidates often misstate. - **Trap:** lowering blood pressure aggressively before securing — **Correct:** control is needed before securing, but aggressive lowering reduces cerebral perfusion. - **Trap:** continuing antithrombotics when a patient presents with headache — **Correct:** antithrombotic drugs are withheld in acute subarachnoid haemorrhage, a favourite stem clue when a patient on anticoagulants presents with headache. ## Frequently asked questions ### What is the best first investigation for suspected subarachnoid haemorrhage? Non-contrast CT of the head is the best first investigation for suspected subarachnoid haemorrhage, and it is most sensitive within six hours of onset. A negative CT performed later, or one with high clinical suspicion, should be followed by lumbar puncture for xanthochromia. ### Why is xanthochromia looked for in lumbar puncture? Xanthochromia is looked for because red cells break down into bilirubin in CSF after subarachnoid haemorrhage, and it becomes detectable after about twelve hours. It supports the diagnosis when CT is negative and helps distinguish true bleeding from a traumatic tap. ### What is the role of nimodipine in subarachnoid haemorrhage? Nimodipine is given in subarachnoid haemorrhage at 60 mg every four hours for 21 days because it improves neurological outcome. It works mainly by protecting against ischaemic injury rather than by preventing angiographic vasospasm. ### What does the Hunt-Hess grade indicate in subarachnoid haemorrhage? The Hunt-Hess grade indicates the clinical severity of subarachnoid haemorrhage, running from grade I with mild headache to grade V with coma. Higher grades predict poorer outcome, and the grade guides the urgency and intensity of neurocritical care. ### When does delayed cerebral ischaemia occur after subarachnoid haemorrhage? Delayed cerebral ischaemia after subarachnoid haemorrhage usually occurs between about day four and day fourteen, peaking around the second week. It is monitored with clinical checks and transcranial Doppler, and treated with euvolaemia and induced hypertension.