Incidental diagnosis of primary intrathoracic goiter on radionuclide 99m-tc pertechnetate radioisotope thyroid scan

Abstract

Retrosternal goiters are classified into two groups. One is the truly primary intrathoracic or aberrant goiter. Presence of accessory thyroid tissue in the mediastinum of these patients group is congenital, with the blood supply derived entirely from intrathoracic vessels and it has no direct connection to the cervical thyroid gland. This primary intrathoracic goiter group represents less than 1% of surgically removed goiters. The much more common second group represents the acquired retrosternal goiter. It arises in the cervical thyroid gland and while growing it descends along a fascial plane, through the thoracic inlet into the mediastinum. Intrathoracic goiters usually present with clinical symptoms due to pressure on adjacent structures as the goiter enlarges within the rigid thoracic inlet. Asymptomatic large retrosternal, especially primary intrathoracic goiters are very uncommon. Here, we report a case of large retrosternal primary intrathoracic goiter found serendipitously on Technetium-99m (99mTc) pertechnetate radioisotope thyroid scan, which was missed on ultrasonogralhy (USG) neck in an asymptomatic patient presented with neck heaviness. Thus, here we emphasize the role of radioisotope thyroid scan over USG neck to diagnose retrosternal goiter.