Intra-thoracic thyroid rests: an updated classification and case series

Thyroid rests are common and arise during embryological development, with aberrant descent of thyroid tissue along the thyro-thymic tract. These give rise to a range of pathologies, including goitre formation and malignancy. Thyroid rests have been graded I-IV based on their connection to the thyroid gland proper - grade I is a short protuberance, grade II & III are connected via a pedicle and fibrous band respectively, and grade IV is completely disconnected. We propose the addition of grade V to describe entirely intra-thoracic disconnected rests. The recognition of Grade V is important, as failure of complete excision may lead to recurrence of a mediastinal goitre, also known as the 'forgotten goitre'.

A retrospective review was performed to include all patients who underwent thyroidectomy for benign retrosternal thyroid disease from January 2015 to January 2022 at the University of Sydney Endocrine Surgical Unit. Data regarding patient demographics, pre-operative work-up, intra-operative findings, histopathology and complications were collated.

Our unit performed 1087 thyroidectomies for benign retrosternal goitre during the study period. Twenty-six Grade V rests were identified in 20 patients (1.8%). Surgery was performed for compressive symptoms in 13 patients, seven were incidental. All patients underwent sternotomy or manubriotomy.

It is important to recognize thyroid rests that are completely disconnected from the thyroid gland. Identification of these rests requires tailored pre-operative work-up, as excision requires access to the thoracic cavity for vascular control. Incomplete excision may lead to development or persistence of the "forgotten goitre" among other pathologies.