Endocrine Abstracts

Thyroid ectopia is a frequent and severe form of congenital hypothyroidism and results from failure of the process of embryonic development and migration of the thyroid gland from the pharyngeal pouch to the anterior neck with the isthmus sited at the level of the cricoid cartilage. With improved technetium scanning techniques, cases of dual foci thyroid tissue are increasingly recognised. The incidence and clinical characteristics of this group of patients has not been established.

Methods: A review of clinical, biochemical, and radiological data from babies referred through the UK newborn screening programme to Great Ormond Street Hospital between 2006 and 2012 with identification of all cases of thyroid ectopia. Anterior and lateral views of the thyroid technetium scans were reviewed by a single consultant in nuclear medicine to establish the presence of one or two foci of thyroid tissue. Clinical and biochemical data from the single and dual foci thyroid groups were compared.

Results: 143 cases were reported to demonstrate thyroid ectopia on technetium scan between 2006 and 2013. Of these 22 (15.4%) had dual foci ectopic thyroid tissue. The initial TSH was lower in the dual foci (177.5 mU/l) compared with single foci (252.1 mU/l) and free T₄ higher in the dual foci than single foci groups (10.38 vs 8.44 pmol/l). The male:female ratio in the dual foci group was 1:3.4 compared to 1:2.6 in the single foci groups. There was no difference in gestation or birth weight between groups. Related pathology was more frequent with single foci.

Discussion: Dual foci thyroid ectopia occurs in 15% of thyroid ectopia and presents with a slightly milder phenotype. It is more common than previously recognised and this divergence of two populations of cells in thyroid embryogenesis with failure of migration requires further genetic evaluation.