**Core Concept**
Cavernous hemangioma is a benign vascular tumor of the orbital tissues, characterized by a retrobulbar location, well-defined capsule, slow progression of proptosis, and a predilection for the 2nd to 4th decades of life. It arises from endothelial cells of the cavernous sinus and is often found within the muscle cone.

**Why the Correct Answer is Right**
Cavernous hemangioma is the most common benign orbital tumor in young adults, typically presenting with slowly progressive proptosis due to expansion of the tumor within the orbital cavity. It has a well-defined capsule, retrobulbar location, and is easily resectable. The tumor is composed of dilated, thin-walled vascular channels and is histologically distinct from other orbital lesions. It is most common in the 2nd to 4th decades, aligning with the clinical presentation.

**Why Each Wrong Option is Incorrect**
Option A: Capillary hemangioma is a small, superficial vascular tumor, usually located in the conjunctiva or extraocular muscles, not retrobulbar, and often presents with sudden onset, not slow progression.
Option C: Lymphangioma is a lymphatic malformation, typically presenting in infancy, with a more diffuse, cystic appearance and not a well-defined retrobulbar mass.
Option D: Hemangiopericytoma is a rare, aggressive vascular tumor, often with a more infiltrative growth pattern, not well-capsulated, and more common in older adults.

**Clinical Pearl / High-Yield Fact**
Cavernous hemangioma is the most common benign orbital tumor in young adults and should be considered in any patient with slowly progressive proptosis and a well-defined retrobulbar mass—especially when resectability is expected.

✓ Correct Answer: B. Cavernous hemangioma