A 50 year old lady is presenting with a retrobulbar orbital tumor within the muscle cone. It has a well defined capsule and presents with slowly progressive proptosis. The diagnosis is:

**Core Concept**
The question tests the ability to diagnose orbital tumors based on their location and characteristics. Orbital tumors can be benign or malignant and vary in their presentation. A retrobulbar orbital tumor within the muscle cone suggests a specific set of differential diagnoses.

**Why the Correct Answer is Right**
Given the description of a well-defined capsule and slowly progressive proptosis, the most likely diagnosis is a **cavernous hemangioma**. This is a common benign orbital tumor that typically presents with gradual proptosis due to its slow growth. The well-defined capsule is characteristic of cavernous hemangiomas, which are usually found within the muscle cone.

**Why Each Wrong Option is Incorrect**
**Option A:** Might be considered if the tumor was more aggressive or had different characteristics.
**Option B:** Could be a possibility but usually presents differently.
**Option D:** Typically has a different presentation and is less common in this context.

**Clinical Pearl / High-Yield Fact**
Cavernous hemangiomas are notable for being the most common benign orbital tumor in adults, often presenting with gradual proptosis and having a characteristic appearance on imaging studies.

**Correct Answer:** C. Cavernous Hemangioma

✓ Correct Answer: D. Cavernous hemangioma