What condition is characterized by enlargement of extraocular muscles with sparing of the tendinous insertions, often leading to proptosis in adults?

Thyroid ophthalmopathy, also known as Graves' disease, is the condition where extraocular muscles enlarge while sparing the tendinous insertions, leading to unilateral or bilateral proptosis. The muscles are affected in the order of Inferior rectus, Medial rectus, Superior rectus, and Lateral rectus (I'M SLow). Key diagnostic features include muscle enlargement on imaging and clinical symptoms such as lid retraction and periorbital edema. A common pitfall is mistaking it for orbital pseudotumor, which typically involves the tendons. Recognizing the pattern of muscle involvement is crucial for accurate diagnosis.