USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

What condition is characterized by fibrous tissue replacement of the thyroid gland and surrounding tissue, and can obstruct the trachea?

1. Follicular adenoma

2. Papillary adenocarcinoma

3. Riedel thyroiditis

4. Toxic multinodular goiter

The correct answer is: Riedel thyroiditis

The condition characterized by fibrous tissue replacement of the thyroid gland and surrounding tissue, which can lead to tracheal obstruction, is indeed Riedel thyroiditis. This rare form of chronic thyroiditis is noted for the extensive fibrotic changes that can invade local structures, often leading to symptoms of compression such as difficulty breathing due to tracheal involvement. Riedel thyroiditis is distinct from other thyroid conditions because it presents not only with thyroid enlargement but also with a hard, woody consistency of the gland. This fibrosis can extend beyond the thyroid gland, affecting adjacent structures. As such, it can manifest as a neck mass and is associated with compressive symptoms. Other thyroid conditions listed have different characteristics and complications. Follicular adenoma is a benign tumor of the thyroid that does not typically cause obstructive symptoms. Papillary adenocarcinoma refers to a common form of thyroid cancer, which may present with a nodule but does not inherently lead to the fibrous replacement of tissue. Toxic multinodular goiter involves hyperfunctioning nodules and is associated with hyperthyroidism rather than fibrous replacement or significant obstruction.