This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Orbit, Subject name: Ophthalmology
What is the cause for enlargement of muscle shown in this CT-scan? 
Select and explain. 
A. Pseudotumor, B. Myositis, C. Rhabdomyosarcoma, D. Grave's ophthalmopathy
D: Grave's ophthalmopathy
Answer: D: Grave's ophthalmopathy 
Explanation: Ans. (d) Grave's ophthalmopathyRef: Parson's, 22/e, p. 487Thyroid eye disease produce typical Fusiform enlargement of extraocular muscles and spares the tendon.