Abstract
Thyroid hemiagenesis (THA) is a rare congenital anomaly in which one lobe of thyroid gland fails to develop during embryological stage. Agenesis may be unilateral, total or isthmic. Left thyroid lobe is more commonly involved than right lobe in hemiagenesis. Agenesis of the isthmus was seen in 50% of cases. Left sided hemiagenesis is more common than right sided hemiagenesis with a Left to right ratio of 4:1. Clinically patients can be euthyroid, hypothyroid or hyperthyroid. Often it is diagnosed as an incidental finding during ultrasonography (USG) study of neck, which can easily diagnose this condition.
 Actual incidence of THA is unknown; most cases are diagnosed in patients admitted for thyroid scan or thyroid surgery because of suspicion of other thyroid abnormalities. This explains high frequency of association of hemiagenesis with other thyroid abnormalities such as multinodular goiter, adenoma, hyperthyroidism, hypothyroidism, chronic thyroiditis, and carcinoma.
 Khaladkar, et al. emphasized that surgeon when planning a thyroidectomy must be aware of rare anatomical variations because such anomalies are not noticed in the differential diagnosis, investigations and treatment.
 We report a rare case of 46 years old female patient who presented with nontoxic nodular goiter and intraoperatively we found a right sided multinodular goiter including the isthmus with complete absence of the left thyroid lobe with ipsilateral inferior parathyroid adenoma which is according to the available studies is the sixth case recorded worldwide till now.
Highlights
Thyroid gland is the first endocrine gland to start developing in the embryo [1]
Right hemithyroidectomy was performed, we found that the left lobe of the thyroid gland was completely absent but there was a big inferior parathyroid adenoma on the ipsilateral side of hemiagenesis and it was excised after we identified the other parathyroid gland which were all normal in size and preserved
The diagnosis of Thyroid hemiagenesis (THA) was established based on sonographic assessment combined with scintiscan, which were performed to exclude the presence of functional thyroid tissue on the contralateral side to the lobe demonstrated in ultrasonography, and to visualize potential accessory or probable ectopic thyroid tissue located ectopically [20]
Summary
Thyroid gland is the first endocrine gland to start developing in the embryo [1]. It is well known for its developmental anomalies such as persistence of pyramidal lobe, thyroglossal duct, agenesis of isthmus, agenesis or hemiagenesis of thyroid gland, or aberrant thyroid glands [2]. The superior parathyroid gland, from the fourth pharyngeal pouch, migrates very little before it rests on the dorsal and superior aspect of the thyroid gland [7] This explains why parathyroid adenomas can be found in association with thyroid hemiagenesis in an anatomically normal position [8]. Disorders that are associated with THA have been largely related to the thyroid gland, but some cases of superimposed parathyroid abnormalities have been reported These are mostly coexisting parathyroid adenomas on the ipsilateral side of THA and have been single or even double [15]. Right hemithyroidectomy (right lobectomy with isthmus) was performed, we found that the left lobe of the thyroid gland was completely absent but there was a big inferior parathyroid adenoma on the ipsilateral side of hemiagenesis and it was excised after we identified the other parathyroid gland which were all normal in size and preserved. The histopathological picture is that of benign parathyroid nonfunctioning oxyphil adenoma with characteristics abundant eosinophilic granular cytoplasmic cytomorphological changes
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