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

What is a key histological feature of papillary adenocarcinoma of the thyroid gland?

1. Presence of psammoma bodies

2. Extensive lymphatic spread

3. Orphan Annie nuclei

4. Hematogenous spread

The correct answer is: Presence of psammoma bodies

A key histological feature of papillary adenocarcinoma of the thyroid gland is the presence of psammoma bodies. Psammoma bodies are calcified structures that can be found in certain types of tumors, particularly those arising from epithelial tissues. In the context of papillary thyroid carcinoma, these structures are commonly observed and are considered a distinct characteristic that helps pathologists differentiate this type of cancer from other thyroid neoplasms. While extensive lymphatic spread and hematogenous spread can occur in various thyroid cancers, they are not specific histological features of papillary adenocarcinoma itself. Similarly, "Orphan Annie nuclei," which refer to nuclei that appear empty due to the loss of chromatin, are indeed associated with papillary thyroid carcinoma but are not as defining as the presence of psammoma bodies. The identification of psammoma bodies is not only a classic histological finding but also reinforces the diagnosis of this tumor type.