**Core Concept**
Pulsatile otorrhoea refers to the abnormal flow of blood through the ear, often accompanied by a palpable pulse or rhythmic sensation. This phenomenon is typically associated with vascular malformations or anomalies in the ear.

**Why the Correct Answer is Right**
Pulsatile otorrhoea is most commonly caused by a glomus tumor, a type of paraganglioma that arises from the glomus body in the middle ear. These tumors are highly vascular and can lead to pulsatile bleeding through the ear canal. The glomus body is a cluster of modified smooth muscle cells and chemoreceptor cells that are involved in regulating blood pressure and detecting changes in oxygen levels.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because pulsatile otorrhoea is not typically associated with acute otitis media, which is an infection of the middle ear. While acute otitis media can cause a range of symptoms, pulsatile bleeding is not a common feature.
**Option B:** This option is incorrect because mastoiditis is an infection of the mastoid bone, which is located behind the ear. While mastoiditis can cause a range of symptoms, pulsatile bleeding is not a typical feature.
**Option C:** This option is incorrect because otosclerosis is a type of bone growth in the middle ear that can cause hearing loss. While otosclerosis can cause a range of symptoms, pulsatile bleeding is not typically associated with this condition.

**Clinical Pearl / High-Yield Fact**
When evaluating a patient with pulsatile otorrhoea, it's essential to consider the possibility of a glomus tumor. These tumors can be difficult to diagnose, but they often present with a characteristic "red, beefy" appearance in the ear canal.

**Correct Answer: C. Otosclerosis is not correct in this case, the answer is actually Glomus Tumour.