THA is a rare congenital anomaly of the thyroid gland with about 800 cases reported in the literature until 2020 . The true prevalence of THA is not clearly known, with the reported prevalence rates varying between 0.05 to 0.5 % . In this report, we present a case of woman diagnosed with left lobe THA without involvement of the isthmus and a right-sided thyroid nodule (TI-RADS 2) on ultrasound. In Uganda, since the introduction of the universal iodization in 1993, iodine fortification of salts has markedly reduced the incidence of goiter . Therefore, it is important than all suspicious lesions are meticulously investigated. In the present case, we cannot completely rule out the possibility of early childhood exposure to iodine deficiency since she was born before the era of universal salt iodization in Uganda.
Patients with THA are most frequently clinically euthyroid as in the present case . However, large case-control studies 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, in patients with THA than in those with bilobate thyroid glands, the most frequent disorders being thyroid nodules and autoimmune thyroid diseases [8, 11]. We found a solitary thyroid nodule in the present case of THA as a reason to seek medical attention.
Most cases of THA are sporadic, however, familial clustering of THA has also been reported [1, 12]. The prime genes mentioned in association with THA include thyroid transcription factors – TTF1 (NKX2–1), TTF2 (FOXE1) and PAX8. Homozygous deletions of one of these genes in animal models led to thyroid dysgenesis of varying severity [1, 13]. The impact of THA on the patient’s general health is not clear. Nonetheless multiple associated conditions have been described in the literature, of which parathyroid abnormalities were the most common [1, 14].
Ultrasonography and radionuclide thyroid scanning are the imaging modalities of choice in the evaluation of the thyroid gland . Thyroid scintigraphy using technetium or iodine can be helpful in the diagnosis of THA but has 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, and inflammatory; and infiltrative diseases of the thyroid [16, 17]. Therefore, scintigraphy findings should be confirmed by ultrasound to avoid false positive results . Ultrasonography is a better diagnostic tool as it is widely available and cost-effective with no radiation exposure to the patient . However, in case of ectopic thyroid gland in the retrosternal or mediastinal location, scintigraphy with I-123 is the investigation of choice as it has high specificity . In our patient, the diagnosis of THA was confirmed with ultrasound of the neck.
TI-RADS lexicon was developed by the American College of Radiology for risk stratification of a thyroid nodule using ultrasound to guide further management . Stratification is based on composition, echogenicity, shape, margin, and echogenic foci of the thyroid nodule. According to the current recommendations, TR1 – benign (no fine needle aspiration (FNA)), TR2 – not suspicious (no FNA), TR3 – mildly suspicious (FNA if ≥ 2.5 cm, follow up if ≥ 1.5 cm), TR4 – moderately suspicious (FNA if ≥ 1.5 cm, follow up if ≥ 1 cm) and TR5 – highly suspicious (FNA if ≥ 1 cm, follow if ≥ 0.5 cm) [21, 22]. Our patient had TR 2, henceforth FNA was not performed.
THA has been considered a benign congenital anomaly requiring no medical or surgical treatment. Nevertheless, the entity has been associated with a high incidence of other associated thyroid disorders. Therefore, the diagnosis of THA should prompt to investigate for other thyroid disorders for early detection and treatment [1, 7, 21].