Thyroid Uptake 99mtc Infant Ectopic

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Fig. 1. Normal thyroid gland in a 4-year-old girl 15 min after intravenous administration of 50 MBq 99mTc pertechnetate. Left panel: lateral view; right panel: anterior view.

considered helpful in the work-up. Scintigraphy added little to the management of children with post-irradiation hypothyroidism, Hashimoto's thyroiditis, or Graves' disease, when the clinical diagnosis was straightforward.

The Normal Thyroid Scintigraphy

The thyroid gland is located in the antero-inferior part of the neck (infrahyoid compartment) (fig. 1). There are two lobes and an isthmus. 10-40% have a small pyramidal lobe, arising from the superior part of the isthmus, which is occasionally identified on scintigraphy.

Congenital Defects

Congenital defects include anatomic and inherited disorders [10]. Anatomic defects comprise agenesis (fig. 2), hemiagenesis and maldescent of the gland, which is positioned along the tract of the thyroglossal duct. Rarely, congenital cysts of the thyroid are seen. The clinical consequences are highly variable, from severe hypothyroidism due to thyroid agenesis to moderate hypothyroidism due to ectopic (usually lingual) (fig. 3) thyroid rudiments or thyroid hypoplasia (fig. 4) and, finally, to subclinical hypothyroidism (high serum TSH with normal serum free T4 and free T3 concentrations) in patients with thyroid hemiagenesis. Imaging is valuable in defining agenesis of the thyroid. On 99mTc scintigraphy, the thyroid is not identified, but there is uptake by salivary glands [11]. Anatomic defects such as hemiagenesis are infrequently identified because they are rare and seldom result in subclinical or clinical hypothyroidism. Rare cases of coexisting hyperthyroidism [12], including TSH

Fig. 2. 99mTc pertechnetate thyroid scintigraphy demonstrating absence of thyroid uptake in a 10-day-old girl with congenital hypothyroidism due to thyroid agenesis (lateral and anterior view).
Lingual Thyroid Scintigraphy
Fig. 3. 99mTc pertechnetate thyroid scintigraphy showing uptake in the lingual region in a neonate (lateral and anterior view) with congenital hypothyroidism.

receptor antibodies resulting in Graves' disease have been described [13]. Most often congenital defects are found incidentally in patients having imaging of the neck for other reasons.

The introduction of neonatal screening programs has enabled early diagnosis and treatment of infants with congenital hypothyroidism (CH) and the prevention of mental retardation [14]. Patients with CH are classified as having developmental abnormalities of the thyroid gland in 85% of the cases. These include ectopic thyroid tissue, aplasia or hypoplasia of the thyroid or a normally located gland with hypothyroidism caused by dyshormogenesis [15] (fig. 5).

Thyroid Uptake 99mtc Infant Ectopic

Fig. 4. 99mTc pertechnetate thyroid scintigraphy (lateral view) showing reduced uptake in a cervical thyroid in a 13-day-old boy with mild congenital hypothyroidism. Additional US demonstrated a 5 X 5 mm large normoechoic thyroid in the midline, not divided into two lobes - findings compatible with thyroid hypoplasia.

Fig. 4. 99mTc pertechnetate thyroid scintigraphy (lateral view) showing reduced uptake in a cervical thyroid in a 13-day-old boy with mild congenital hypothyroidism. Additional US demonstrated a 5 X 5 mm large normoechoic thyroid in the midline, not divided into two lobes - findings compatible with thyroid hypoplasia.

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