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FALSE-POSITIVE I-131 ACTIVITY IN A PATIENT WITH THYROID CANCER
Authored By: Keith Fischer and Kartikeya Kantawala.
Patient: 70 year old male
History: 70 year old male: Papillary carcinoma of the thyroid, status post complete thyroidectomy. He was subsequently treated with 100 mCi of radioactive I-131.
Evaluate for residual functioning thyroid tissue.
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Fig. 1

Fig. 2
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Findings: RADIOPHARMACEUTICAL: 5.1 mCi I-131 sodium iodide p.o

FINDINGS: Images of the head, neck, trunk, and proximal extremities were obtained 44 hours after oral administration of I-131 sodium iodide.  There is expected I-131 activity in the salivary glands, colon, and urinary bladder. A band of linear uptake is seen in the right mediastinum.
Diagnosis: 1. No residual functioning thyroid tissue.

2. The mediastinal uptake correlates to physiologic uptake in an intrathoracic stomach in this patient with known esophageal cancer, status post resection and gastric pull-through procedure.
General Discussion:

FULL PATIENT HISTORY:

70 year old man with follicular variant of papillary thyroid cancer. He had complete thyroidectomy in March 2007 followed by 100 mCi of radioactive iodine in April 2007. Post-treatment scan showed uptake in the thyroid bed only with physiologic uptake in the intrathoracic stomach.

He also has a history of T1 adenocarcinoma of the distal esophagus for which he had resection and gastric pull-through procedure in October 2005.

DISCUSSION:

Whole body I-131 scan is a well-established imaging method for the detection of metastatic or residual tumor sites in patients with well-differentiated thyroid cancer. However, there are many potential causes of false-positive I-131 scan findings. False positive results may be caused by a wide variety of non-thyroidal neoplasms, which can concentrate radioiodine or from skin contaminated by urine, sweat, or saliva.

Brucker-Davis et al. classified many false-positive findings into four main groups: elimination of iodine through body fluids, infection or inflammation, cyst or transduates, and non-thyroidal tumors.


Potential sites that can mimic thyroid cancer metastases are liver, gall bladder, various causes of an intrathoracic stomach and hiatal hernia, renal cyst, ectopic kidney, focal bronchiectasis and pericardial effusion.

References:

1. Ju-won Seok et al; Normal Gallbladder Visualization during Post-Ablative Iodine-131 Scan

of Thyroid Cancer;J Korean Med Sci 2005; 20: 521-3


2. Freeman M, Roach P, Robinson B, Shields M. Hiatal hernia in iodine-131 scintigraphy: a potential cause of false-positive midline thoracic uptake. Clin Nucl Med 2003; 28: 709-10.


3. Kurtaran A, Ozer S, Kienast O, Dobrozemsky G, Dudczak R. Retained esophagus uptake of iodine-131 in a patient with papillary thyroid carcinoma mimicking a mediastinal mass. Thyroid 2003; 13: 225.

4. Achong DM, Oates E, Lee SL, Doherty FJ. Gallbladder visualization during post-therapy iodine-131 imaging of thyroid carcinoma. J Nucl Med 1991; 32: 2275-7.


5. McEwan LM, Fong W. Unusual extrathyroidal iodine accumulation in a post-ablative I-131 scan. Austral Rad 2001; 45: 512-3.

6. Brucker-Davis F, Reynolds JC, Skarulis MC, Fraker DL, Alexander HR, Weintraub BO, Robbins J. False-positive iodine-131 whole body scans due to cholecystitis and sebaceous cyst. J Nucl Med 1996; 37: 1690-3.

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Additional Details:

Case Number: 120039Owner(s): Keith Fischer and Kartikeya KantawalaLast Updated: 02-07-2013
Anatomy: Face and Neck   Pathology: Neoplasm
Modality: Nuc MedAccess Level: Readable by all users, writable by NucMed Certifiers
Keywords: trnmACR: 20000.12172, 20000.12174

Case has been viewed 43 times.
Certified by Keith Fischer on 11-02-2010

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