Could a Bronchogenic Cyst Present as an I-131-avid, 99m Tc-Non-Avid Lesion and Mimic Metastatic Thyroid Cancer?
Kuan-Chieh Chen, Yi-Ming Chang, Hsing-Hao Su et al.
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Case in brief
A 54-year-old man with papillary thyroid carcinoma underwent thyroidectomy and subsequent imaging. A 99m Tc scan showed no thyroid remnant but identified a 3.5-cm left lung lesion with faint uptake on SPECT/CT, raising concern for metastasis. After I-131 therapy, scans on days 3 and 7 showed intense uptake in the lesion. Surgical excision established the diagnosis of a benign bronchogenic cyst; testing was negative for thyroglobulin, TTF-1, BRAF V600E, and PAX-8. The proposed explanation for I-131 uptake was NIS-mediated uptake or mucinous content.
What made this case unusual
The benign bronchogenic cyst showed intense I-131 avidity despite only faint 99m Tc uptake, mimicking metastatic thyroid cancer.
Diagnostic / clinical pearl
I-131 avidity in a lung lesion does not establish thyroid cancer metastasis; consider a bronchogenic cyst and use tissue confirmation when needed to resolve the diagnosis.