Thyroid hemiagenesis is a rare congenital anomaly of thyroid with about 300 cases reported in the literature until 2010(8). It is three times more common in females as compared to males. In 80% the hemiagenesis involves the left lobe of thyroid gland (with left to right ratio 4:1) and about 50% of patients with left lobe hemiagenesis will also have an absent thyroid isthmus (5, 9). The present case was female and had no known family history of thyroid abnormality. Left lobe hemiagenesis without involvement of the isthmus was found on ultrasound.
Patients with hemiagenesis of thyroid gland are most frequently clinically euthyroid as in the present case (6). However, a large case-control study observed a significantly higher incidence of concomitant thyroid disorders such as Gravesʼ disease, Hashimotoʼs thyroiditis, subacute thyroiditis, nodular goiter, hyper functioning adenoma, primary carcinoma, and metastatic carcinoma, the most frequent disorders being thyroid nodules and autoimmune thyroid disease than subjects with bilobate thyroid glands (10). We found solitary thyroid nodule in the present case of hemiagenesis as a reason to seek medical attention.
Ultrasonography (US) and radionuclide thyroid scanning are the imaging modalities of choice in the evaluation of the thyroid gland (11). Thyroid scintigraphy using technetium or iodine can be helpful in hemiagenesis of thyroid gland but showed drawbacks due to artefacts related to non-visualization of one thyroid lobe due to neoplasm, contralateral autonomous solitary thyroid nodule that is suppressing normal tissue, inflammatory, and infiltrative diseases of the thyroid (12, 13). Therefore, scintigraphy findings should be supplemented by ultrasound to avoid false positive results (14). Ultrasonography is a better diagnostic tool as it is widely available and cost-effective with no radiation exposure to the patient (15). The patient was examined with ultrasound of the neck and laboratory tests of thyroid function test.
Thyroid hemiagenesis has been considered benign congenital anomaly that requiring no medical or surgical treatment. Nevertheless, the entity has been associated with high incidence of associated thyroid disorders as mentioned earlier. Therefore, early detection of those disorders, follow up and intervention when indicated are of paramount importance (6, 16).