Usefulness of Ultrasonography in The Diagnosis of The Etiology of Congenital Hypothyroidism Comparing with Radioisotope Scanning

Congenital hypothyroidism (CH) is the most prevalent preventable cause of mental retardation. Since it is impossible to determine the etiology of CH by biochemical tests per se, imaging modalities of thyroid gland are used to evaluate the morphology and function of this gland and among them radionuclide scanning is currently the gold standard. Considering the limitations of time and accessibility of radioisotope scanning and benefits and faults of ultrasonography in determination of etiology of CH, the aim of this study was to determine the usefulness of sonography as compared to the gold standard imaging method of scintigraphy, in the diagnosis of etiology of primary congenital hypothyroidism in the screening program of Isfahan. This study was conducted from May 2002-February 2007. In order to compare ultrasonography to thyroid scintigraphy for etiologic diagnosis of CH, 102 CH newborns examined by both thyroid scintigraphy and ultrasonography were included in this study. The ultrasonographic findings were compared with the standard-of-reference scintigraphic findings and the sensitivity, specificity of the ultrasonography were determined. According to results of the ultrasonography 63, 27, 3 and 9 infants had normal thyroid glands, agenesia, ectopia and hypoplasia respectively and based on scintigraphic results 57, 36 and 9 of them had normal thyroid gland, agenesia and ectopia respectively. Ultrasound detected sensitivity, specificity, positive predictive value, negative predictive value, LR+ and LR- were 86%, 86%, 90%, 90%, 6.1 and 0.16 respectively. The sensitivity and specificity of ultrasonography compared with thyroid scintigraphy in diagnosis of thyroid gland ectopia was 33% and 100% respectively. Although calculated sensitivity and specificity of this method was not equal to those of thyroid radioisotope scanning but had an acceptable range, thyroid ultrasonography is a relatively appropriate imaging tool for diagnosing thyroid dysgenesia. Hence ultrasonography can be used as the first imaging tool for diagnosing CH, especially when the family prefers not to have the infant scanned.