**Question:** An elderly man who has had a trivial history of head injury three months ago, develops headache and turns unconscious. On examination, he is found to have fixed left dilated pupil and right hemiplegia. What is the most likely diagnosis -

A. Subarachnoid haemorrhage
B. Intracranial abscess
C. Ischaemic stroke
D. Traumatic subarachnoid haemorrhage

**Core Concept:**

The question presents a patient with a history of trivial head injury and subsequent neurological symptoms, which include headache, altered consciousness, and focal neurological deficits (fixed left pupil dilation and right hemiplegia). These findings indicate a potential neurological emergency, and we need to differentiate between the possible causes: subarachnoid haemorrhage, intracranial abscess, ischaemic stroke, and traumatic subarachnoid haemorrhage.

**Why the Correct Answer is Right:**

The correct answer, D. Traumatic subarachnoid haemorrhage, is chosen due to the patient's recent trivial head injury history and the specific neurological symptoms. Traumatic subarachnoid haemorrhage (SAH) is caused by a ruptured blood vessel within the subarachnoid space, leading to bleeding and subsequent neurological deficits. In this case, the patient's history of head injury and the focal neurological deficits align with traumatic SAH.

**Why Other Options are Incorrect:**

A. Subarachnoid haemorrhage (SAH) is caused by spontaneous rupture of an artery within the subarachnoid space. In this scenario, the recent trivial history of head injury excludes spontaneous SAH as the primary cause.

B. An intracranial abscess is an infection within the brain, typically caused by bacteria. The provided clinical presentation does not align with an intracranial abscess, as the history of head injury and neurological deficits are more consistent with traumatic insult rather than a bacterial infection.

C. Ischaemic stroke occurs due to impaired blood flow to a cerebral artery territory. Although the patient's history of head injury and neurological deficits are concerning, the clinical picture does not specifically align with ischaemic stroke, particularly given the recent history of trauma.

**Clinical Pearl:**

When assessing a patient with a history of recent head injury and neurological deficits, consider traumatic subarachnoid haemorrhage as a possible diagnosis, especially if the symptoms align with the history provided. In this case, the patient's recent trivial head injury and focal neurological deficits are more in line with traumatic SAH than spontaneous SAH. Prompt recognition of this condition is crucial for appropriate management, as traumatic SAH often presents differently from spontaneous SAH and requires a different diagnostic approach and treatment strategy.