Endocrine Abstracts

Introduction: Thyroid imaging is of proven help in establishing a diagnosis of congenital hypothyroidism in newly referred infants. Radio-isotope and/or ultrasound imaging is commonly used; each has weaknesses but have complimentary strengths and thus have been used in combination in our centre since 1999. We undertook a retrospective review and analysis of ultrasound imaging in infants with proven thyroid ectopia to re-examine the diagnoses.

Patients and methods: Eighteen infants with proven thyroid ectopia on radio-isotope scanning were reassessed. Fifteen were found to have useable images. Thyroid biochemistry at the time of diagnosis was also reviewed.

Results: All infants showed the presence of tissue bilaterally in the thyroid fossa. This tissue was deemed to be non-thyroidal in nature since, apart from being non-functional on isotope scan, it exhibited some or all of the following typical features: hyperechogenicity, heterogeneity, significantly smaller size than normal neonatal thyroid (P≤0.001), poor vascularity and anechoic and/or hypoechoic cystic areas. A striking and consistent ultrasonographic finding was the extension of this tissue behind and around the great vessels of the neck – a previously unreported feature. Quantitative thyroglobulin measured at diagnosis was highly variable (2–612 μg/l) although the median value was 181.5 μg/l.

Conclusion: Considerable experience is required to interpret ultrasound data in neonates with abnormal thyroid function. We caution against diagnosing dysplastic thyroid in situ on the basis of ultrasound alone, particularly if the tissue exhibits any of the features we describe which are associated with non-thyroidal, cervical tissue found in situ in proven thyroid ectopia. A combination of initial venous thyroid function, including thyroglobulin measurement, and dual ultrasound and isotope scanning enhances diagnostic accuracy.