A 40-year-old female patient complains of a persistent headache. A CT scan of the head was performed, as shown below. What is the most accurate diagnosis?

Explanation

## Correct Answer: B. Subarachnoid hemorrhage (SAH) Subarachnoid hemorrhage (SAH) presents with a characteristic **hyperdense appearance in the basal cisterns and sulci** on non-contrast CT, which is the pathognomonic finding in this case. The blood fills the cerebrospinal fluid (CSF) spaces between the arachnoid membrane and the pia mater, creating a distinctive pattern that appears as hyperdense material in the subarachnoid space rather than in a localized collection. In India, SAH is most commonly caused by rupture of berry aneurysms (80% of non-traumatic cases), followed by arteriovenous malformations and hypertensive hemorrhage. The classic presentation includes sudden-onset thunderclap headache, neck stiffness, photophobia, and meningeal signs. CT is the gold standard for acute SAH diagnosis within 6 hours of symptom onset, with sensitivity >95%. The distribution of blood in the basal cisterns, Sylvian fissures, and sulci is the key discriminating feature. If CT is negative but clinical suspicion remains high, lumbar puncture showing xanthochromia confirms the diagnosis. Management follows the Indian guidelines with early aneurysm identification (CT angiography or digital subtraction angiography), nimodipine for vasospasm prevention, and neurosurgical intervention as indicated. ## Why the other options are wrong **A. Epidural hemorrhage** — Epidural hemorrhage produces a **lens-shaped (biconvex) collection** that does not cross suture lines, typically located between the skull and dura. It appears as a localized hyperdense mass, not diffuse hyperdensity in the basal cisterns and sulci. The classic mechanism is traumatic tearing of the middle meningeal artery, presenting with lucid interval. This is a common NBE trap because both are intracranial bleeds, but the location and CT morphology are distinctly different. **C. Intraparenchymal hemorrhage** — Intraparenchymal (intracerebral) hemorrhage shows **hyperdensity within the brain substance itself**, often with surrounding edema and mass effect. It does not fill the subarachnoid spaces or basal cisterns diffusely. Common causes include hypertension, amyloid angiopathy, and anticoagulation. The location is within gray or white matter, not in the CSF spaces, making it radiologically distinct from the diffuse subarachnoid pattern seen here. **D. Subdural hemorrhage** — Subdural hemorrhage appears as a **crescent-shaped collection** between the dura and brain surface, crossing suture lines (unlike epidural). It can be acute (hyperdense), subacute (isodense), or chronic (hypodense). The key difference is that subdural blood is localized between dura and brain, not distributed throughout the subarachnoid space and basal cisterns. This distinction is critical for differentiating the two most common intracranial bleeds in Indian trauma practice. ## High-Yield Facts - **SAH CT finding**: Hyperdense material in basal cisterns, Sylvian fissures, and sulci (not localized collection) - **Berry aneurysm rupture** accounts for 80% of non-traumatic SAH in India; anterior communicating artery most common site - **Nimodipine** is the standard DOC for vasospasm prevention in SAH (60 mg every 4 hours for 21 days per Indian guidelines) - **CT sensitivity >95%** within 6 hours of SAH; decreases to 50% by day 5, necessitating LP with xanthochromia if clinical suspicion persists - **Thunderclap headache** (sudden, maximal intensity at onset) is the classic presentation; meningeal signs develop within hours - **CTA or DSA** is mandatory after SAH diagnosis to identify aneurysm location and guide neurosurgical intervention ## Mnemonics **BLEED LOCATION (Intracranial hemorrhages)** **E**pidural = lens-shaped, **S**ubdural = crescent, **S**ubarachnoid = diffuse in cisterns, **I**ntraparenchymal = within brain. Use: Quickly recall CT morphology for each bleed type. **SAH MANAGEMENT (NIMO)** **N**imodipine, **I**maging (CTA/DSA), **M**eningeal signs, **O**bservation for rebleeding. Use: Bedside management checklist for acute SAH. ## NBE Trap NBE commonly pairs epidural and subdural hemorrhage with SAH to test whether students can distinguish **localized collections (lens or crescent) from diffuse hyperdensity in CSF spaces**. The trap is assuming "intracranial bleed = epidural or subdural" without carefully analyzing the CT distribution pattern. ## Clinical Pearl In Indian emergency departments, a 40-year-old woman with sudden thunderclap headache and neck stiffness is SAH until proven otherwise—even if CT appears normal, LP with xanthochromia is mandatory. Early recognition and nimodipine initiation within 4 hours significantly reduce vasospasm-related morbidity and mortality. _Reference: Robbins Ch. 28 (Nervous System); Harrison Ch. 434 (Stroke); Bailey & Love Ch. 52 (Neurosurgery)_