**Question:** A 20 year old male comes to casualty with head injury. Examination reveals normal consciousness, clinically normal, and blood in the tympanic membrane. Most likely cause is:

A. Traumatic tympanic membrane perforation
B. Subarachnoid haemorrhage
C. Closed head injury
D. Middle ear infection (otitis media)

**Core Concept:**

Head injuries can present with various symptoms and signs, depending on the severity and location of the injury. Among the options provided, we need to identify the most likely cause of the blood in the tympanic membrane.

**Why the Correct Answer is Right:**

The correct answer is **B. Subarachnoid haemorrhage (SAH)**. Subarachnoid haemorrhage is a type of brain hemorrhage that occurs when blood leaks into the subarachnoid space, the area between the inner lining of the skull (dura mater) and the brain. In this case, the presence of blood in the tympanic membrane indicates that the blood has likely leaked from the subdural or subarachnoid space, leading to the bleeding in the middle ear (tympanic membrane).

**Why Each Wrong Option is Incorrect:**

A. **Traumatic tympanic membrane perforation (Option A)** is a tear or rupture in the eardrum (tympanic membrane), which is a different condition than the one described in the question. A traumatic tympanic membrane perforation would typically present with symptoms like pain, otorrhoea (ear discharge), and hearing loss, not blood in the tympanic membrane.

C. **Closed head injury (Option C)** is a broader term for any injury to the head, which could include various types of hemorrhages, fractures, or contusions. However, the presence of blood in the tympanic membrane already narrows down the possibilities, making Subarachnoid haemorrhage a more likely cause.

D. **Middle ear infection (Otitis media) (Option D)** is a common condition characterized by inflammation and infection of the middle ear. This option is incorrect because the presence of blood indicates a more severe hemorrhage, rather than inflammation. Blood in the tympanic membrane is more consistent with SAH (Subarachnoid haemorrhage).

**Clinical Pearls:**

1. **Clinical Pearls:** The question presents an example of a rare but severe presentation of a more common condition, making it essential for students to recognize that blood in the tympanic membrane is not a typical symptom of middle ear infections but is more consistent with SAH.

2. **Clinical Pearls:** In clinical practice, a middle ear infection (Otitis media) would present with otalgia (ear pain), otorrhoea (ear discharge), and tympanic membrane redness or inflammation (infection). The presence of blood in the tympanic membrane suggests a more severe hemorrhage rather than an infection or inflammation.