SAT-478 A Case of Congenital Thyroid Hemi-Agenesis- Caution for Complications!

Introduction: Congenital Thyroid hemi-agenesis is an uncommon clinical entity. We present a case highlighting the importance of awareness of this condition and the need to evaluate and manage co-existing hypothyroidism and risk of malignancy. Case: A 20 year old female known to have Hashimoto’s thyroiditis (non-adherent to levothyroxine), and hemi-agenesis of left lobe of thyroid gland, presented with right-sided thyroid enlargement. She was clinically euthyroid. Physical exam: enlarged right sided thyroid gland with palpable anterior cervical lymphadenopathy. Left lobe could not be palpated. TFTs were notable for TSH 4.98 uIU/ml (0.358-3.74) and Free T4 0.79 ng/dl (0.76-1.46) consistent with sub-clinical hypothyroidism while Anti TPO antibody was positive at 8332.8 U/mL (0 - 60). CBC negative for leukocytosis. US thyroid: left-sided thyroid agenesis with intact isthmus and enlargement of right lobe of the thyroid 7.7 cm x 1.6 cm x 2.6 cm with 2 sub-centimeter hypoechoic solid nodules and 2 enlarged lymph nodes 1.5 cm and 2.3 cm (not found in US thyroid 2 years ago) Levothyroxine was re-started. ENT evaluation determined that her lymphadenopathy was benign and consistent with Hashimoto’s thyroiditis. Subsequent TFTs improved. Discussion: Thyroid Gland embryogenesis occurs in the 4(th) week of fetal life. Subsequent abnormal bilobal differentiation of the thyroid gland is presumed to be the etiology of congenital hemi-agenesis. Its prevalence in several studies is estimated to be between 0.05-0.25%. It is symptomatic pre-dominantly in females and may have familial origin with vast majority of cases having left hemi-agenesis with intact isthmus. It is helpful to know that most symptomatic patients have compensatory hypertrophy of the remnant lobe. It is important to remember that compensatory enlargement of the remnant lobe in the setting of hypothyroidism may be a sign of insufficient endogenous thyroxine production and/or replacement. Although rarely symptomatic, hemi-thyroid remnant may need to be evaluated for co-existing hyperthyroidism, hypothyroidism, carcinoma and multinodular goiter among others, with hypothyroidism thought to be the most common. US thyroid is a useful modality to help guide the evaluation of patients with hemi-agenesis. Awareness of this congenital condition is key in preventing unnecessary evaluations and interventions. Non-resolving lymphadenopathy in Hashimoto’s thyroiditis must be evaluated for lymphoma, however, based on studies, no additional risk of malignancy was identified in patients with underlying thyroid hemi-agenesis. References: Y.H. Wu, R.O. Wein, B. Carter Thyroid hemiagenesis: a case series and review of the literature Am J Otolaryngol, 33 (3) (2012), pp. 299-302