**Question:** A road traffic accident patient in the casualty is comatose with unilaterally dilated pupil. The NCCT of the patient shows a Lesion peripherally present with concavo-convex border. What is the probable diagnosis?

**Core Concept:** Concavo-convex border on NCCT (Non-Contrast Computed Tomography) scan is a characteristic feature of a subdural hematoma (SDH), a type of head injury. A subdural hematoma occurs when there is bleeding between the dura mater and arachnoid mater, causing a mass effect on the brain.

**Why the Correct Answer is Right:** In this scenario, the patient presents with coma and unilateral dilated pupil, which points towards a possible traumatic brain injury. Furthermore, the NCCT scan reveals a peripheral, concavo-convex border lesion, which is a characteristic feature of subdural hematoma. The peripheral location and concavo-convex border help distinguish it from other types of brain lesions.

**Why Each Wrong Option is Incorrect:**

A. **Answer A (Contusion):** Contusions are localized areas of brain tissue injury with no specific borderline. The concavo-convex border is not a feature of contusions.

B. **Answer B (Edema):** Brain edema is a general increase in brain volume due to fluid accumulation. It does not present with a peripheral, concavo-convex border on NCCT scan, unlike subdural hematoma.

C. **Answer C (Oedema):** Similar to option B, cerebral oedema is a general brain swelling without specific scan findings.

D. **Answer D (Haematoma):** A general term for a collection of blood outside the blood vessels. Haematoma is not specific to subdural hematoma and lacks the characteristic concavo-convex border on NCCT scan.

**Clinical Pearl:** Traumatic brain injury, specifically a subdural hematoma, should be considered in patients with coma and unilateral dilated pupil following a head injury. The characteristic NCCT scan findings aid in confirming the diagnosis.