A 34-year-old woman comes to the office because of a painless lump in her neck that she noticed two weeks ago. She reports no difficulty swallowing, shortness of breath, or changes in the quality of her voice. Her past medical history is significant for localized radiation therapy to the neck for a cutaneous hemangioma during her early childhood. She does not take any medications and has no known allergies. She has never smoked cigarettes and drinks alcohol only on social occasions. Her temperature is 37.0 C (98.6°F), blood pressure is 118/76 mmHg, pulse is 72/min, and respirations are 14/min. Physical examination reveals a firm, 2.2-cm, non-tender nodule in the right lobe of the thyroid gland that moves upward when the patient swallows. A single, 1.5-cm, non-tender lymph node is palpable in the right level II cervical chain. The remainder of the physical examination is unremarkable. Serum thyroid-stimulating hormone level is 1.8 uU/mL. Ultrasound of the thyroid demonstrates a hypoechoic nodule with irregular borders and internal microcalcifications. Fine-needle aspiration of the nodule is performed, and cytology reveals clusters of cells with overlapping, enlarged nuclei containing clear centers.
Which of the following is the most likely diagnosis?
The correct answer is:
D) Papillary thyroid carcinoma
Papillary thyroid carcinoma is the most common form of thyroid cancer and is frequently associated with a history of ionizing radiation exposure to the head and neck. It typically presents as a painless, slow-growing thyroid nodule in a patient who is euthyroid. The hallmark cytological feature is the presence of enlarged nuclei with a cleared-out appearance due to dispersed chromatin, often referred to as Orphan Annie eye nuclei. Other characteristic findings include psammoma bodies, which are laminated calcifications, and nuclear grooves.
Answer choice A: Anaplastic thyroid carcinoma, is incorrect. This is an extremely aggressive malignancy that usually affects older adults, typically in their 60s or 70s. It presents as a rapidly enlarging, painful neck mass that often causes compressive symptoms like dysphagia or hoarseness early in the course.
Answer choice B: Follicular thyroid carcinoma, is incorrect. This cancer typically spreads through the bloodstream to distant sites like the bones or lungs. A key limitation of fine-needle aspiration is that it cannot differentiate between follicular adenoma and follicular carcinoma because the diagnosis of malignancy depends on identifying capsular or vascular invasion, which requires a complete surgical specimen.
Answer choice C: Medullary thyroid carcinoma, is incorrect. This malignancy originates from the calcitonin-secreting parafollicular C cells. It can occur sporadically or as part of Multiple Endocrine Neoplasia type 2A or 2B syndromes. Histological evaluation would show nests of malignant cells in an amyloid stroma rather than the clear nuclei seen in this patient.
Answer choice E: Thyroid lymphoma, is incorrect. This rare malignancy is strongly associated with pre-existing Hashimoto thyroiditis. It usually presents as a rapidly expanding thyroid mass in an older patient and is characterized by a dense infiltration of lymphocytes rather than the specific epithelial nuclear features described.
Key Learning Point
Papillary thyroid carcinoma is the most prevalent thyroid malignancy and is often linked to childhood radiation exposure. Diagnosis is made via fine-needle aspiration showing characteristic nuclear features such as clear centers and nuclear grooves.
