Unexpected finding of thyroid hemiagenesis in a patient presenting with a right thyroid nodule and a history of Poland syndrome

Introduction: Poland syndrome is defined primarily by congenital absence of the pectoralis major. Thyroid hemiagenesis is the congenital absence of a single thyroid lobe. The combination of both pathologies has not been previously described. Case presentation: Poland syndrome is a rare congenital condition characterised by aplasia or hypoplasia of the pectoralis major muscle, associated to varying degrees with malformation of the ipsilateral upper limb. It is often accompanied by other congenital abnormalities, but the presence of a single thyroid lobe is exceptional. We report to our knowledge the first observation of thyroid hemiagenesis and Poland syndrome. Observation: A 19-year-old female was referred for chronic right neck swelling. On physical examination, she had a relatively small stature but an overall normal appearance. Neck examination revealed a mobile 3 cm right firm thyroid nodule. There was complete absence of the left breast and pectoralis muscles, with normal development on the right. The left hand was relatively small and exhibited syndactyly. Biochemical testing revealed normal thyroid function. Neck ultrasound revealed complete absence of the left thyroid lobe and the presence of a well-circumscribed hypoechoic 3 cm right thyroid nodule without calcifications, TIRADS score 3. The patient was diagnosed with Poland syndrome, a 3 cm right thyroid nodule, and agenesis of the left thyroid lobe. Her consent was obtained for a right thyroid lobectomy due to the cosmetic impact of the nodule, as well as the small risk that this represented a thyroid malignancy. An uncomplicated right thyroid lobectomy was performed. Final surgical pathology was consistent with a 3 cm benign follicular adenoma. Conclusion: Poland syndrome and thyroid hemiagenesis are both rare congenital malformations. Their association has not been previously described. Prior to surgery, the patient must be informed of the mandatory need for lifelong thyroid hormone replacement.