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Diagnostic Imaging Modalities in Congenital Hypothyroidism

« Back to Volume 22, Issue 3, September 2006 - Table of Contents

Newborn screening for congenital hypothyroidism (CH) is one of the major achievements of preventive medicine. This condition occurs frequently and early diagnosis and treatment have been shown to prevent brain damage and the ensuing mental retardation. The etiology of CH may play an important role in determining disease severity, outcome, and therefore, its treatment schedule. Radionuclide imaging (RI) is currently the most precise diagnostic technique to establish the etiology of CH. Conventional ultrasound can identify an athyrotic condition at the normal neck position and has gained acceptance for the initial evaluation of CH; however, its ability in delineating ectopic thyroid is limited.

Dr. Ohnishi and colleagues used color Doppler ultrasonography (CDU) to assess blood flow and morphology in the detection of ectopic thyroid in CH patients. Eleven patients (7 females, 4 males), who had elevated TSH levels by a neonatal mass screening program and who had absent thyroid glands at the normal neck position by the standard gray-scale ultrasonography (GSU), were enrolled in this study. None of the patients had a family history of thyroid diseases. All of the patients underwent CDU, GSU, MRI, and RI investigations. The findings on CDU, GSU, and MRI were compared with those of RI, and the sensitivities for detecting ectopic thyroid were calculated.

Diagnoses by different diagnostic modalities are shown (Table). Based on RI findings by either 99mTc-pertecnetate or 123I-sodium iodine studies, 10 patients were diagnosed as CH with ectopic thyroid and one patient with undetectable serum thyroglobulin (<5 ng/ml [the normal range in childhood is 5–35 ng/ml]) as CH with athyreosis. Peripheral or internal color flow signal on CDU was depicted clearly in 9 patients. The area of the signal imaging detected by CDU corresponded to thyroid tissue found by RI. The GSU showed 7 ectopic thyroids as a hypoechoic mass or a hyperechoic mass to the surrounding tissue. GSU failed to detect 3 ectopic thyroids. The MRI detected ectopic thyroid as rounded masses with higher signal intensity than that of the surrounding tissue in both the T1-weighted and T2-weighted images. A total of 7 ectopic thyroids were clearly detected by MRI. The MRI failed to detect 3 ectopic thyroids, like GSU.

The sensitivity of CDU, GSU, and MRI for detecting ectopic thyroids was 90, 70, and 70%, respectively. Onishi et al. concluded that CDU is superior to GSU and MRI for detecting ectopic thyroids and that CDU may be adopted as the diagnostic tool for the initial investigation of suspected CH.

Ohnishi H, Sato H, Noda H , Inomata H, Sasaki N . J Clin Endocrinol Metab. 2003;88:5145–5149.

First Editor’s Comment

CH causes irreversible mental retardation without T₄ replacement from early life. Since the implementation of newborn screening programs for CH, early diagnosis and treatment usually begins around the first week of life, resulting in a dramatic improvement in the outcomes of intellectual potential of affected infants. Permanent primary CH affects one newborn in ~3000–4000. The causes of CH are thyroid agenesis or hypolasia, present in 20%–40% of the cases, ectopic thyroid detected in 45%–60%, and dyshormonogenesis which accounts for the remaining 10%–15% of cases. The etiology of CH may be important in determining disease severity, outcome, and treatment schedule, with higher treatment doses and close monitoring required, particularly early in life, in patients with athyreosis.

The most precise diagnostic technique to establish the etiology of CH has been RI; a high TSH level and undetectable thyroglobulin levels indicate athyreosis. In the late 1970s, standard GSU was recognized as a potential method for evaluating the anatomy of the thyroid gland. The GSU has recently gained acceptance in evaluation of the etiology of CH since it has the advantage of ready availability, noninvasiveness, and low cost; however, its ability in identifying ectopic thyroid glands is not as satisfactory nor as reliable as RI. Although MRI may identify lingual thyroids, its clinical usefulness in the diagnosis of patients with CH has not been established. Both GSU and MRI were of low sensitivity (70%) in the diagnosis of the precise cause of CH.

The CDU provides not only the standard gray-scale image, but also a color display of blood flow and, hence, permits the evaluation of thyroid vascularity. Nevertheless, CDU had not been reported for detecting ectopic thyroid. Ohnishi et al assessed the ability of CDU to establish the presence of ectopic thyroid tissue in patients with CH. This method compared with the imaging of RI, GSU, and MRI showed that CDU had a sensitivity of 90% and was superior to GSU and MRI. The researchers concluded that CDU has an advantage over GSU and MRI in its ability to image ectopic thyroid. They felt that this technique may be adopted as the first choice of a diagnostic tool at the initial investigation for suspected CH. However, further studies are required to compare CDU with the various methods of RI before it can be established as the technique of choice to determine the type of CH.

Yoshikazu Nishi , MD

Second Editor’s Comment

Although this paper from Japan was published 3 years ago is important in the management of CH patients. Unfortunately the technology described is not yet widely available.

Fima Lifshitz, MD

Last Updated: 6/12/2009