Right-sided thyroid hemiagenesis with enlarged isthmus and lingual ectopic thyroid tissue presenting as nodular goiter: case report and literature review.

Introduction and importance: Thyroid hemiagenesis (THA) is a very rare congenital anomaly defined by the underdevelopment or complete absence of one thyroid lobe. Similarly, ectopic thyroid tissue (ETT) is a rare condition where thyroid tissue is located outside its usual anatomical position, most often at the tongue base. The simultaneous occurrence of THA and ETT is extremely rare, as demonstrated in our case. Case presentation: A 30-year-old female presented with a long-standing history of anterior neck swelling. Ultrasound revealed right THA along with enlarged isthmus. Fine needle aspiration indicated a follicular neoplasm (Bethesda category IV). A contrast-enhanced CT scan confirmed the findings and incidentally identified a well-enhancing lesion at the tongue base. A thyroid scan confirmed its thyroid origin. A PET scan ruled out malignancy in both the cervical and lingual lesions. A subsequent incisional biopsy of the lingual ETT performed two months later also confirmed the absence of malignancy. The patient underwent a total thyroidectomy and was referred for radioactive iodine ablation therapy to address the lingual lesion. The procedure was well-tolerated, and the patient experienced an uneventful recovery. Clinical discussion: THA is most often diagnosed incidentally as it's mostly asymptomatic through imaging modalities such as ultrasonography or thyroid scintigraphy, or during surgical procedures. Since it is generally asymptomatic, THA itself does not require management. Conclusion: This case emphasizes the complexities of THA, especially when coexisting with ETT. The potential for neoplastic transformation and the development of hypothyroid symptoms heightens the importance of timely diagnosis and intervention.