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Ectopic Lingual Thyroid
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Case Study Compiled by Ashely Gordon, student technologist

William Butts, CNMT,
The Brown Imaging Center,
Augusta, Georgia

Current Study Findings

Following oral administration of 13.54 uCi of I-131 NaI, a twenty four hour uptake is obtained. The twenty-four hour uptake is 9%. Normal range (in this clinical setting) is 10-30%

Following intravenous administration of 16.71 mCi of 99mTc Pertechnetate, multiple images of the neck are obtained including a broad view with markers (at the chin and supersternal notch), an anterior image, and LAO, and RAO. The examination shows decreased activity in the lower neck just above the sternum. There is increased activity in the pharynx which likely represents the base of the tongue which likely represents lingular thyroid tissue. Clinical correlation is recommended/

Patient History

A 33 year old female presents with ectopic tissue at the base of her tongue. Laboratory TSH is elevated. She presents with no other signs or symptoms.


Discussion

Developmental Anatomy

The thyroid gland is a small endcrine gland in the front of the neck. It is made up of two lobes that lie along the windpipe. During development, the thyroid gland originates in the back of the tongue, but it normally migrates to the front of the neck before birth. Sometimes it fails to migrate properly and is located high in the neck or even in back of the tongue, which we see in this case. This is very rare. The thyroid gland can also migrate too far and end up in the chest -- a condition known as substernal thyroid. The exact cause of these disorders remains unknown. By the end of the first trimester, the thyroid gland is not only located in its normal location in the neck, but it is also capable of collecting iodine from fetal circulation for the production of thyroid hormone. By the time the fetus reaches full term, the thyroid system is fully functional.

Thyroid Feedback Axis

The function of the thyroid gland is to take iodine, found in many foods, and convert it to thyroid hormones T4 and T3. Thyroid cells are the only cells in the body which can absorb iodine. These cells combine iodine and the amino acid tyrosine to make T3 and T4. These hormones are then released into the blood and transported through the body where they influence metabolism. The thyroid gland is under the control of the pituitary gland and when the levels of T3 and T4 drop too low, the pituitary gland produces thyroid stimulating hormone, or TSH. Under the influence of TSH, the thyroid will secrete T3 and T4. The pituitary will then decrease TSH production. The pituitary gland is under the influence of the hypothalamus that produces TRH, Thyroid releasing hormone. TRH tells the pituitary to release TSH.

Functional Evaluation

Measuring the amounts of TSH and T4/T3 levelsin the blood can tell us whether the patient may have a thyroid disorder. Also, an iodine uptake scan can measure how much iodine is taken up by the thyroid gland. Hypothyroid patients usually take up too little iodine and hyperthyroid patients take up too much iodine. Radioactive iodine, I-131 is (organified) in the thyroid gland or excreted in the urine over the next few hours after administration. The amount of iodine that goes into the thyroid gland is then measured by a thyroid uptake. Patients on thyroid medication will have a low uptake because their own thyroid is not functioning. The normal 24 hour uptake of iodine is 10-30%. In this case we see that the uptake is low normal at 9%. The patient presented with elevated levels of TSH which could be indicative of hypothyroidism if T4 levels are low. Interpretation of iodine uptake should be done in conjunction with laboratory blood tests.

Conclusion

A thyroid scan gives a picture of how well the thyroid gland is functioning. 99mTc Pertechnetate is used in the scan because it is a monovalent anion trapped by the thyroid gland in the same matter as iodine, (although Tc04 does not undergo organification). After trapping, pertechnetate slowly washes from the thyroid gland. Iodine and pertechnetate both share the same active transport uptake pathway. Hypofunctioning glands will appear less intense than the salivary glands and hyperfunctioning glands will appear hotter than the salivary glands. Normal uptake was seen on this scan except that lingual thyroid tissue is likely.