**Core Concept**
The question is testing the identification of a specific type of ear discharge associated with a particular lesion. The underlying concept is the relationship between ear discharge and the underlying pathology, specifically the types of lesions that cause different characteristics of discharge.

**Why the Correct Answer is Right**
The correct answer is **Chronic Otitis Media with Cholesteatoma**. Cholesteatoma is a type of skin cyst that forms in the middle ear, and it is characterized by a scanty, foul-smelling, and painless discharge. This is due to the accumulation of dead skin cells and debris within the cyst, which leads to a foul odor and a minimal amount of discharge. The painlessness of the discharge is due to the fact that the cyst is located in a closed space, and the pressure within the cyst is equal to the pressure outside, preventing any discomfort.

**Why Each Wrong Option is Incorrect**
* **Option A:** Mastoiditis is an infection of the mastoid bone, which is located behind the ear. It is characterized by pain, fever, and discharge, but not typically scanty or foul-smelling.
* **Option B:** Otosclerosis is a type of bone growth in the middle ear that can cause hearing loss, but it is not associated with discharge.
* **Option D:** Eustachian tube dysfunction can cause a sensation of fullness in the ear and difficulty hearing, but it is not typically associated with scanty or foul-smelling discharge.

**Clinical Pearl / High-Yield Fact**
Remember that a scanty, foul-smelling, painless discharge from the ear is highly suggestive of a cholesteatoma, and further investigation and imaging are necessary to confirm the diagnosis.

**Correct Answer: C. Chronic Otitis Media with Cholesteatoma**