False-Positive Uptake of I-131 in a Laryngocele Mimicking Thyroid Remnant After Thyroidectomy for Papillary Thyroid Carcinoma

Abstract

A 66-year-old woman underwent total thyroidectomy for papillary thyroid carcinoma stage pT4 followed by radioiodine therapy with 3.7 GBq (100 mCi) iodine-131. Radioiodine therapy revealed intense radioiodine uptake of the neck, which was interpreted as thyroid remnant tissue. Follow-up whole-body scans with iodine-131 in hypothyroidism 3 months and 1 year after radioiodine therapy revealed focal uptake in the neck. Computed tomography and gadolinium-enhanced MRI of the neck demonstrated an ovoid lesion in the larynx without gadolinium enhancement. Neither thyroid remnant tissue nor enlarged cervical lymph nodes could be demonstrated either on CT or on MRI. Further examination of the patient in the ear, nose and throat department confirmed the finding of a laryngocele and biopsies demonstrated benign tissue. Follow-up whole-body scans with iodine-131 in hypothyroidism 3 years and after injection of rhTSH 5 years after radioiodine therapy reproduced the focal uptake in the neck. After initial radioiodine therapy thyroglobulin levels were never measurable, not at any of the whole-body scans in hypothyroidism, after rhTSH, or at intermediate follow-up examinations under TSH-suppressive levothyroxine therapy. The patient declined definitive operative revision of the laryngocele and is in good health 8 years after the diagnosis of papillary thyroid carcinoma.

Scintigraphic Visualization of Glossal Thyroid Tissue During the Follow-up of Thyroid Cancer Patients

“…For example, Schmidt et al reported on uptake in a laryngocele. 13 Usually, lingual thyroid tissue is not visible on the first ablation I-131 scan, and becomes apparent on successive diagnostic scans. In fact, in a large number of cases, ectopic foci lie clinically and metabolically dormant, unless stimulated by hormonal changes.…”