Hypothyroidism following removal of a "thyroglossal duct cyst".

This case demonstrates how a midline ectopic thyroid gland can be misdiagnosed as a thyroglossal duct cyst. Awareness of this clinical entity is critical if the diagnosis is to be made preoperatively. Thyroid function tests and a 99mTc or 123I scintiscan of the neck should be performed when evaluating a patient with a midline anterior cervical mass. Although thyroid replacement will often cause regression of the enlarged ectopic thyroid gland, surgical intervention is required if a solid mass persists. When an ectopic thyroid gland has been excised and is subsequently found to be the child's only thyroid tissue, thyroid replacement is necessary. If biopsy of the mass established the diagnosis at the time of surgery, effective treatment consists of longitudinally dividing the tissue and placing each half laterally beneath the strap muscles. When this is done, long-term follow-up and periodic thyroid function tests are advised. If this tissue should become hypoactive, thyroid replacement is then required.