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THYROID ABNORMALITIES The median thyroid anlage may, on rare occasions, fail to develop. The resultant athyrosis, or absence of the thyroid gland, is associated with cretinism. The anlage also may differentiate in locations other than the isthmus and lateral lobes. The most common developmental abnormality, if looked on as such, is the pyramidal lobe (Fig. 18), which has been reported to be present in as many as 80% of patients in whom the gland was surgically exposed. Usually, the pyramidal lobe is small; however, in Graves’ disease or in lymphocytic thyroiditis, it is often enlarged and is commonly clinically palpable. The pyramidal lobe generally lies in the midline but can arise from either lobe. Origin from the left lobe is more common than is origin from the right lobe. 72 THYROID HEMIAGENESIS More than 100 cases have been reported in which only one lobe of the thyroid is present. 73 The left lobe is absent in 80% of these patients. Often, the thyroid lobe that is present is enlarged, and both hyperthyroidism and hypothyroidism have been reported at times. Females are affected
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