Endocrinology Fellow PGY 5 Grand Strand Medical Center Myrtle Beach, South Carolina, United States
Introduction : Thyroid hemiagenesis is a rare congenital disorder characterized by an absence of one thyroid lobe. It is usually incidentally diagnosed during imaging of the neck region. The prevalence of this condition is reported to vary from 0.05% to 0.5%, although the true frequency is uncertain. We report a case of follicular adenoma of oncocytic type with associated KRAS mutation in a patient with thyroid hemiagenesis.
Case(s) Description : A 59-year-old female with a past medical history of hyperlipidemia, asthma, and seasonal allergies was evaluated for chronic hoarseness of voice which was present for 10 years. She underwent laryngoscopy and was noted to have asymmetry of vocal wave and right vocal cord stiffness. She was planned to undergo transnasal vocal fold augmentation, and preoperative CT scan of the head and neck showed a large multinodular right thyroid lobe with a dominant nodule of approximately 1.5 cm. The patient had a subsequent thyroid ultrasound which showed an absent left thyroid lobe with a multinodular remaining right lobe with a solid, isoechoic dominant nodule of 1.7 x 1.2 x 1 cm. Fine needle aspiration cytology showed Atypia of Undetermined Significance (AUS) with some Hurthle cell components. Molecular testing with Thyroseq V3 indicated a 50 - 60% probability of cancer with KRAS mutation. She was referred to endocrine surgery and underwent total thyroidectomy. Surgical pathology showed follicular adenoma, oncocytic type without malignancy.
Discussion : Thyroid hemiagenesis is often associated with functional and morphological abnormalities of the thyroid gland including autoimmune thyroid disease or thyroiditis, multinodular goiter, differentiated thyroid cancer, and/or other developmental disorders including thyroglossal duct cyst, ectopic thyroid. Our patient had an indeterminate nodule with Hurthle cell predominance. The use of molecular testing is beneficial in proper diagnosis and risk stratification of thyroid nodules with indeterminate FNA cytology. In a recent retrospective analysis of consecutive FNA samples from primary thyroid nodules clinically tested by ThyroSeq v3, out of 40622 samples of AUS, 71% had a benign call rate after molecular testing. In a study of 204 thyroid fine-needle aspiration cases positive for RAS mutations with corresponding surgical pathology resection specimens, KRAS mutation was associated with a significantly lower carcinoma outcome when compared with HRAS61 and NRAS61 mutations. Further studies need to be done to risk stratify and determine the value of conservative management of indeterminate thyroid nodules with KRAS mutations.
