Haemotympanum is the accumulation of blood in the middle ear cavity, often resulting from blunt head trauma that causes bleeding within the temporal bone or middle ear without perforating the tympanic membrane. The bluish discoloration observed behind an intact tympanic membrane is a classic sign of haemotympanum. The presence of blood dampens the vibration of the tympanic membrane and ossicles, leading to a conductive hearing loss, typically around 40 dB.

Fracture of the stapes or malleus (options a and b): These are less likely without direct trauma to the temporal bone or severe force. Ossicular fractures usually result in a more significant hearing loss and may show discontinuity on imaging.
Perilymph fistula (option d): This involves a leak of inner ear fluid into the middle ear, usually causing sensorineural hearing loss and vertigo, not a conductive hearing loss.
Tympanic membrane perforation (option e): Would present with a visible perforation on otoscopy and often a history of barotrauma or direct injury to the ear canal.
Further Reading:

Bluestone CD, Simons JP. Pediatric Otolaryngology. 5th ed. Saunders; 2014.
Gulya AJ, Minor LB, Poe DS. Glasscock-Shambaugh Surgery of the Ear. 6th ed. People's Medical Publishing House; 2010.
Smith JA, Danner CJ. Complications of temporal bone trauma. Otolaryngol Clin North Am. 2008;41(3):567-584.
Additional Concepts:

Exam Focus: For the FRCS (ORL-HNS) Examination, it's crucial to recognize key clinical signs and correlate them with the most probable diagnosis. Haemotympanum is a high-yield topic, especially distinguishing it from other causes of hearing loss post-trauma.

Anatomy Review: Understand the anatomy of the middle ear and how trauma can affect structures like the ossicles, tympanic membrane, and inner ear fluids.

Diagnostic Approach: Be prepared to discuss the diagnostic steps, including when to order imaging such as a CT scan to rule out temporal bone fractures or ossicular chain disruptions.

Management Strategies: Know that haemotympanum often resolves spontaneously and requires conservative management. However, awareness of potential complications and indications for surgical intervention is essential.

Pediatric Considerations: Children may present differently than adults. Their symptoms and signs can be subtle, and examination techniques may need to be adjusted accordingly.

Common Pitfalls: Be cautious not to overlook haemotympanum due to its subtle presentation. In exams, ensure you interpret otoscopic findings accurately and link them to the patient's history.