**Core Concept**
Chronic Suppurative Otitis Media (CSOM) is a chronic infection of the middle ear that can lead to various complications due to the destruction of the middle ear structures. The commonest complication of CSOM is often related to the spread of infection to adjacent structures.

**Why the Correct Answer is Right**
The commonest complication of CSOM is **Chronic Otitis Media with Cholesteatoma**. This occurs when keratin debris accumulates in the middle ear, leading to the formation of a cholesteatoma, a type of skin cyst. The cholesteatoma can erode the ossicles, inner ear structures, and the temporal bone, causing hearing loss, facial paralysis, and intracranial complications. The formation of cholesteatoma is facilitated by the destruction of the tympanic membrane and the ossicles, which allows the accumulation of keratin debris.

**Why Each Wrong Option is Incorrect**
* **Option A:** Meningitis is a potential complication of CSOM, but it is not the commonest complication. Meningitis occurs when the infection spreads to the meninges, often through a direct extension from the middle ear.
* **Option B:** Labyrinthitis is an inner ear infection that can be a complication of CSOM, but it is not the commonest complication. Labyrinthitis occurs when the infection spreads to the inner ear, leading to vertigo, hearing loss, and balance problems.
* **Option C:** Facial paralysis can be a complication of CSOM due to the erosion of the facial nerve by the cholesteatoma, but it is not the commonest complication. Facial paralysis can occur in up to 20% of cases of CSOM, but it is not as common as cholesteatoma formation.

**Clinical Pearl / High-Yield Fact**
The key to preventing complications of CSOM is early diagnosis and treatment. Regular follow-up and monitoring of patients with CSOM can help identify complications early, and prompt treatment can prevent long-term damage.

**Correct Answer:** C. Cholesteatoma.