Parasitic thyroid nodules: cancer or not?

Area of Science:

• Endocrinology
• Nuclear Medicine
• Surgical Pathology

Background:

• A 58-year-old woman presented with thyrotoxicosis 14 years after a hemithyroidectomy for a benign follicular adenoma.
• Imaging revealed cervical lymphadenopathy with suspicious tracer uptake, initially suspected as metastatic thyroid cancer.

Purpose of the Study:

• To investigate the cause of thyrotoxicosis in a patient with lateral neck thyroid deposits.
• To evaluate the role of radioactive iodine in managing benign parasitic thyroid nodules.

Main Methods:

• Ultrasound, Technetium-99m uptake scan, fine-needle aspiration with thyroglobulin washings.
• Completion thyroidectomy, bilateral cervical lymph node dissection, and radioactive iodine (3.7 GBq) ablation.
• Histopathological analysis and BRAF V600E mutation testing of thyroid tissue.

Main Results:

• Histology confirmed benign multinodularity and 24 parasitic thyroid nodules in the left lateral neck, with reactive lymphadenopathy.
• Post-radioactive iodine treatment, serum thyroglobulin became undetectable, and follow-up showed no recurrence.
• BRAF V600E mutation analysis of parasitic thyroid tissue was negative.

Conclusions:

• Thyrotoxicosis from lateral neck functional thyroid tissue can be due to benign parasitic nodules, a rare differential diagnosis after thyroid surgery.
• Parasitic thyroid nodules, potentially from surgical implantation, may necessitate radioactive iodine ablation due to difficulty in complete resection.
• Negative BRAF mutation analysis in parasitic thyroid tissue aids in excluding papillary thyroid carcinoma.