The rare variant of thyroid congenital abnormality, thyroid hemiagenesis refers disorders in which one thyroid lobe fails to develop or regress. This abnormality usually involves the left lobe of the thyroid gland
1. Because of most patients do not have any signs or symptoms thyroid disease, the true prevalence of thyroid hemiagenesis is not known. However, reports estimate prevalence at between 1:1900 and 1:2675.
2. Reported cases indicates that absence of the left lobe is more common (about 80% of the cases) and the isthmus was absent in 44-50 % of cases. In our case the left lobe was absent. The etiology of thyroid hemiagenesis is not clearly known. Aberrant thyroid migration and genetic component involving mutations in this or in several genes that are known to control thyroid morphogenesis/migration has been suggested
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Thyroid hemiagenesis is usually is associated with a variety of thyroid abnormalities, including Graves disease4, chronic lymphocytic thyroiditis, subacute thyroiditis5 nodular goiter2, hyper functioning adenoma, primary or metastatic carcinoma and rarely with hypothyroidism6. Our case was asymptomatic.
The diagnosis of thyroid hemiagenesis is based upon ultrasonography in most patients, as ultrasound is commonly available, cheap and easily employed technique, which also has been found efficient for the diagnosis of thyroid hemiagenesis. CT, MRI and scintigraphy are also useful in diagnose thyroid hemiagenesis but as they are more expensive and time demanding with no superiority to ultrasonography in diagnose thyroid hemiagenesis.
3D-US provides additional detailed diagnostic information compared to the 2D-US. The recent introduction of three-dimensional ultrasound (3D US) and advances in computer technology has provided better image resolution, acquisition and storing. With many advantages the volume sonography is to become routine imaging technology to clinical practice provided an advance in imaging technology. This technique allows simultaneous demonstration of 3 orthogonal planes. With this technique entire volume of anatomy can be reconstructed in any plane and this presents significant advantage for diagnosis and geometric measurements. Thus, 3D-US combines the relatively low cost, ease and convenience of conventional ultrasound with the advantage of obtaining unlimited planar reformatted sections7,8.
In conclusion, in our case, hemiagenesis of thyroid is discovered incidentally when patient are evaluated for other disorder and confirmed literature knowledge about diagnose and localization. True diagnosis of this rare silent abnormality with efficient imaging methods is of importance to save the patients from unnecessary surgery and iodine therapy and also US is a useful and reliable method for evaluating and detecting thyroid abnormalities.
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