Diagnosis of ectopic thyroid: value of pretracheal soft-tissue measurements.

Thyroid ectopia, dysgenesis, or agenesis has been conventionally diagnosed with the use of radioisotope scanning procedures. This report proposes the use of a conventional lateral radiograph of the neck to determine the presence or absence of the thyroid gland in its normal anatomic position. The thyroid gland is ensheathed by the pretracheal layer of the deep cervical fascia anterior to the trachea. The gland's presence or absence can be determined by calculating the ratio of the soft-tissue measurements between the anterior wall of the trachea and both the outer margin of the skin and the margin of the subcutaneous fat as determined from a lateral radiograph of the neck. This "pretracheal ratio" may be used to accurately differentiate between a lingual thyroid and other masses at the base of the tongue.