Most common cause of unilateral proptosis in adults is –
**Core Concept**
Thyroid-related orbitopathy is the most common cause of unilateral proptosis in adults, resulting from autoimmune inflammation and fibrosis of the orbital tissues. This condition is often associated with Graves' disease.
**Why the Correct Answer is Right**
The correct answer is due to the autoimmune nature of Graves' disease, which leads to an increase in orbital tissue volume. This expansion is caused by the infiltration of lymphocytes and plasma cells, as well as the deposition of mucopolysaccharides. The resulting inflammation and fibrosis lead to the characteristic proptosis seen in thyroid-related orbitopathy. The extraocular muscles are also affected, leading to strabismus and diplopia.
**Why Each Wrong Option is Incorrect**
**Option A:** Carotid-cavernous fistula is a rare cause of proptosis, typically presenting with pulsatile proptosis and bruit on examination. This option is incorrect because it is a less common cause of unilateral proptosis.
**Option B:** Orbital cellulitis is an infection of the orbital tissues, typically caused by bacterial or fungal pathogens. This option is incorrect because it is more commonly bilateral and associated with fever and pain.
**Option C:** Orbital lymphoma is a type of cancer that affects the orbital tissues, but it is less common than thyroid-related orbitopathy. This option is incorrect because it is a less common cause of unilateral proptosis.
**Clinical Pearl / High-Yield Fact**
When evaluating unilateral proptosis, it is essential to consider thyroid-related orbitopathy as a primary differential diagnosis. A thorough history and physical examination, including assessment of the thyroid gland, should be performed to guide further evaluation and management.
**Correct Answer:** C. Orbital lymphoma