**Core Concept**
Pulsatile otorrhoea refers to the abnormal pulsatile flow of blood or cerebrospinal fluid from the ear. This condition is often associated with abnormalities in the vascular or neurological structures of the temporal bone.

**Why the Correct Answer is Right**
Pulsatile otorrhoea is typically seen in cases of a glomus jugulare tumor, which is a type of paraganglioma arising from the jugular bulb. This tumor can erode into the jugular vein, leading to abnormal pulsatile flow of blood from the ear. The exact mechanism involves the tumor's invasion into the jugular vein, causing a communication between the high-pressure arterial system and the lower-pressure venous system, resulting in the characteristic pulsatile otorrhoea.

**Why Each Wrong Option is Incorrect**
**Option A:** Mastoiditis is an infection of the mastoid air cells, which can cause otorrhoea but is not typically pulsatile. The flow of pus or fluid in mastoiditis is not pulsatile due to the absence of a direct communication with the arterial system.
**Option B:** Otosclerosis is a condition of abnormal bone growth in the middle ear, leading to hearing loss. While it can cause otorrhoea, the flow is not typically pulsatile due to the absence of a vascular connection.
**Option C:** Perilymphatic fistula is a condition where there is a communication between the perilymphatic space and the middle ear or external environment, leading to otorrhoea. However, the flow is not typically pulsatile, as it is not directly connected to the arterial system.

**Clinical Pearl / High-Yield Fact**
When encountering a patient with pulsatile otorrhoea, it is essential to consider the possibility of a glomus jugulare tumor, which requires prompt evaluation and management to prevent complications.

**Correct Answer: D. Glomus jugulare tumor.**