Endocrine Abstracts

Introduction: The thyroid gland, shaped like a butterfly with two lobes connected by the isthmus, is a common site for nodule formation. Only 2-9% thyroid cancers occur in the isthmus. Cancers in the isthmus are more prone to spread beyond the thyroid, leading to a less favourable prognosis. While ultrasound features like a taller-than-wide shape and microcalcifications suggest malignancy in lobar nodules, suspicious characteristics in isthmus nodules are underreported.

Case presentation: A 54-year-old male non-smoker with bronchial asthma, presented with persistent hoarseness of voice for 2 months, facial puffiness, and giddiness. He denied throat pain, fever, cough, dysphagia, or dyspnoea. On examination no palpable neck nodule, lymphadenopathy, or oral cavity abnormalities. CECT of the neck and thorax identified a hypo-enhancing thyroid nodule in isthmus measuring 12 mm × 8 mm. USG confirmed a well-defined isoechoic nodule with a small central cystic component in the left isthmus, classified as TIRADS 3, without calcifications or internal vascularity. Fibre optic laryngoscopy showed mild sluggish movement of the left true vocal cord (TVC) and a small vocal cord nodule on the right side. Fine-needle aspiration cytology (FNAC) was suspicious for papillary thyroid carcinoma (Bethesda V). Thyroid function tests showed a TSH level of 3.34 with normal FT4 and negative anti-TPO antibodies.

Conclusion: Recent studies indicate that thyroid carcinomas in the isthmus have a worse prognosis than those in other locations, with higher rates of lymph node metastases and extrathyroidal extension. This may be due to the isthmus’s smaller size, thinner structure, and unique lymphatic drainage. These findings, along with the observation that malignant nodules in the isthmus tend to be smaller, suggest the need for revised American College of Radiology TI-RADS algorithms and new biopsy cutoff values for nodules in this region. This case highlights the importance of thorough evaluation and management of thyroid nodules in the isthmus due to their unique characteristics and prognostic implications.