Thyroid hemiagenesis and incidentally discovered papillary thyroid cancer: Case report and review of the literature

While performing a systematic ultrasound study of the thyroid gland volume for the evaluation of iodine deficiency in 2845 normal Belgian school children, we found an absence of the left lobe in 6 children (4 girls and 2 boys). There was no association with other thyroid malformations or dysfunction. This first systematic ultrasound evaluation of thyroid hemiagenesis in normal children established a prevalence of thyroid hemiagenesis of 0.2% and confirmed the female predominance and higher incidence of agenesis of the left lobe.

Permanent primary congenital hypothyroidism (CH) can be caused by abnormal thyroid differentiation (athyreosis), migration (ectopy), or function (leading to goiter). Goiters follow an autosomal recessive pattern of inheritance, whereas ectopy and athyreosis are considered as a single sporadic entity with a female preponderance. On the other hand, a high prevalence of extrathyroidal malformations has been reported in CH, but without linking specific defects to specific types of CH. On the basis of TSH screening, 273 newborns were referred to an academic pediatric endocrinology clinic in the province of Quebec between 1988 and 1997. Of 230 patients with permanent primary CH who had scintigraphy at diagnosis, 141 had ectopy (104 girls), 36 had athyreosis (21 girls), 42 had goiter (18 girls), 10 (3 girls) had a normal scan, and 1 girl had hemiagenesis. Only in the ectopies was the proportion of girls significantly higher than 0.5 (P<0.001). Isolated cardiac malformations were observed in 7 patients (3.0%), a prevalence 5-fold higher than that in the general population; this was largely due to atrial and ventricular septal defects, which were only observed in ectopy and athyreosis. Our data suggest that the molecular mechanisms that lead to complete absence of thyroid differentiation or defective thyroid migration 1) may be similar, but are modulated by the genetic makeup of the embryo and/or the hormonal milieu of the fetus; and 2) may also be involved in septation of the embryonic heart.

Congenital hypothyroidism (CH) is most frequently caused by thyroid developmental abnormalities and it has recently been seen to have a familial component. The aim of this study was to investigate whether thyroid developmental abnormalities exist in first degree relatives of CH children with thyroid dysgenesis, an anomaly which, when present, is sometimes asymptomatic. Thyroid ultrasonography and function were evaluated among first degree relatives (n = 241) of 84 isolated CH children with thyroid dysgenesis. The results were compared with those of an unselected control population (n = 217). In 19 individuals (7.9% of cases) belonging to 18 families (21.4%), 21 cases of thyroid developmental abnormalities were detected, whereas only 2 subjects (0.9%) were affected in controls (P < 0.001). These 21 thyroid developmental abnormalities included thyroglossal duct cysts (n = 14), additional thyroid tissue with presence of a pyramidal lobe (n = 3), thyroid hemiagenesis (n = 3), and ectopic thyroid tissue (n = 1). All of these subjects showed normal thyroid function and belonged to nuclear families of CH children with athyreosis (n = 8), ectopic thyroid tissue (n = 9), or hemiagenesis (n = 1). A segregation analysis led to the conclusion that thyroid developmental abnormalities are compatible with an autosomal dominant mode of inheritance with a low penetrance estimated at 21% for asymptomatic thyroid developmental abnormalities and a probability of less than 7% of developing CH for a carrier of the susceptibility allele. In conclusion, these observations support the hypothesis of a common genetic component of the disorder with heterogeneous phenotypes.