Heterogeneous tissue in the thyroid fossa on ultrasound in infants with proven thyroid ectopia on isotope scan--a diagnostic trap.

BACKGROUND

Thyroid imaging is of proven help in establishing a diagnosis of congenital hypothyroidism in infants. US often shows tissue in the thyroid fossa when radionuclide scintigraphy reveals only ectopic uptake.

OBJECTIVE

Our hypothesis was that the use of US alone could lead to the mistaken diagnosis of normal or dysplastic thyroid in cases of scintigraphy-proven thyroid ectopia.

MATERIALS AND

METHODS

We undertook a detailed retrospective review and analysis of imaging and concurrent biochemistry in infants with thyroid ectopia, confirmed by radionuclide scintigraphy.

RESULTS

Eighteen infants had thyroid ectopia; ten of the original US reports had suggested that cervical thyroid tissue was present. Review showed bilateral tissue in the thyroid fossa in all that was non-thyroidal in nature since, apart from showing no radionuclide uptake, it exhibited some or all of the following typical features: hyperechogenicity, heterogeneity, small size, poor vascularity, and anechoic and/or hypoechoic cysts. Also, extension of the tissue both around and behind the large cervical blood vessels was a universal finding.

CONCLUSION

Considerable experience is required to interpret neonatal thyroid US. We caution against diagnosing a dysplastic/hypoplastic thyroid gland in situ on the basis of US alone, particularly if the tissue exhibits any of the non-thyroidal features described.