What is the most likely diagnosis for a 18-year-old boy with a 1cm swelling adjacent to the thyroid and normal thyroid function?

In this scenario, the most likely diagnosis for an 18-year-old boy with a 1 cm swelling adjacent to the thyroid and normal thyroid function is papillary carcinoma. This type of thyroid cancer is the most common form found in young adults and is characterized by its slow-growing nature and typically good prognosis. Papillary carcinoma often presents as a solitary nodule, which aligns with the clinical finding of a 1 cm swelling.

The patient’s normal thyroid function indicates that the swelling is unlikely to be related to hyperthyroid or hypothyroid states, which further supports the potential for a malignancy like papillary carcinoma rather than other types that may be associated with functional abnormalities.

In contrast, follicular carcinoma, while also a type of thyroid cancer, is less common in this age group and more typically presents in a larger, more invasive form. Lymphoma may present with a rapidly enlarging mass but often affects those over the age of 60 and may cause systemic symptoms like B symptoms (fever, night sweats, weight loss). Anaplastic carcinoma is extremely rare in someone this young and is an aggressive form that typically presents with more severe features and caustic symptoms.

Thus, given the age, the specific characteristics