Medullary thyroid cancer arising from a thyroid rest: a case report

Area of Science:

• Endocrinology
• Oncology
• Pathology

Background:

• Medullary thyroid carcinoma (MTC) is a rare neuroendocrine tumor originating from thyroid C cells.
• Most MTC cases present with a primary thyroid lesion, making extrathyroidal presentations uncommon.
• This report focuses on a unique case of MTC without evidence of an intrathyroidal primary tumor.

Observation:

• A 67-year-old woman presented with a neck mass but no intrathyroidal disease on initial imaging.
• Positron emission tomography-computed tomography (PET-CT) identified paratracheal lymphadenopathy.
• Fine-needle aspiration was inconclusive, initially suggesting metastatic pulmonary neuroendocrine carcinoma due to thyroid transcription factor-1 (TTF-1) positivity.

Findings:

• Pathology review and elevated calcitonin and carcinoembryonic antigen (CEA) levels raised suspicion for MTC.
• Total thyroidectomy and neck dissection revealed no intrathyroidal MTC or C cell hyperplasia.
• Lymph node findings confirmed metastatic MTC originating from an ectopic thyroid rest, a rare entity.

Implications:

• This case underscores the importance of considering MTC in the differential diagnosis of neck masses, even without a clear thyroid primary.
• The findings highlight the possibility of MTC arising from ectopic thyroid tissue.
• Further investigation into rare presentations of MTC is warranted to improve diagnostic and therapeutic strategies.