Computed tomography findings of thyroid hemiagenesis: differentiation from hemithyroidectomy

OBJECTIVES: Thyroid hemiagenesis is a rare congenital anomaly characterized by the lack of development of one thyroid lobe. The purpose of this study was to evaluate computed tomography (CT) findings of thyroid hemiagenesis and to establish useful CT criteria for differentiating thyroid hemiagenesis from the hemithyroidectomy state. METHODS: The CT images of 11 patients with thyroid hemiagenesis were retrospectively reviewed and compared with those of 100 (49 left and 51 right) patients in a hemithyroidectomy state. Image analysis was performed according to the following CT parameters: (a) side of thyroid hemiagenesis, (b) edge of the medial end of the remnant thyroid gland, (c) location of the medial end of the remnant thyroid gland, expressed as the angle of the medial end and (d) any other thyroid abnormality observed during the initial examination. RESULTS: The missing lobe occurred more often in the left than in the right lobe (72.7% vs. 27.3%) as well as concomitant isthmus agenesis (100% vs. 37.5%). The sharp edge of the medial end of the remnant thyroid gland was more common in thyroid hemiagenesis (64%) than in hemithyroidectomy (26%) (P = 0.0153). In left thyroid hemiagenesis, the angle of the medial end (63%) was more frequently > + 30° than in hemithyroidectomy (0%) (P < 0.0001). Two patients presented with hypothyroidism; the remaining nine showed a normal thyroid function. The associated thyroid diseases were autoimmune thyroiditis (n = 1) and papillary thyroid carcinoma (n = 1). CONCLUSIONS: The sharp edge of the medial end of the remnant thyroid gland and an angle of > + 30° for the medial end in cases wherein the left lobe is absent are useful CT features for distinguishing thyroid hemiagenesis from hemithyroidectomy.