**Core Concept**
Modified radical mastoidectomy is a surgical procedure to remove diseased mastoid air cells and sometimes parts of the middle ear. This procedure is often performed to treat chronic otitis media or mastoiditis. Post-operative complications such as persistent ear discharge and retro-orbital pain can occur due to various factors.

**Why the Correct Answer is Right**
The patient's symptoms of persistent ear discharge and retro-orbital pain after a modified radical mastoidectomy are suggestive of a condition called **Cerebrospinal Fluid (CSF) Otorrhea**. This occurs when there is a leakage of CSF from the subarachnoid space into the ear canal, often as a result of a communication between the middle ear and the subarachnoid space. This can be due to the surgical procedure itself, or it can be a complication of the original disease process.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is likely incorrect because it does not directly relate to the symptoms described and the surgical procedure performed.
* **Option B:** This option might be a distractor related to other post-operative complications, but it does not specifically address the symptoms of CSF otorrhea.
* **Option D:** This option might be a distractor related to other complications of the surgical procedure, but it does not directly relate to the symptoms of CSF otorrhea.

**Clinical Pearl / High-Yield Fact**
CSF otorrhea can be a life-threatening condition if not promptly treated, as it can lead to meningitis or other central nervous system infections. It is essential to recognize this condition early and manage it appropriately.

**Correct Answer:** C. Cerebrospinal Fluid (CSF) Otorrhea.