We would like to alert our surgical colleagues to the potential of obtaining false positive FDG-PET/CT ( 18 F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography) results in the presence of tuberculosis.
The most common cause of false positive FDG-PET study in clinical oncology setting is the uptake of 18 F-FDG ( 18 F-Fluorodeoxyglucose) in the areas of infection and inflammation; with the increasing application of this molecular imaging technique in various cancers there is growing appreciation of this among the PET interpreting physicians . This has prompted investigators from various centres across the world to carry out full-fledged prospective evaluation study to re-ascertain the usefulness and the true accuracy of FDG-PET/CT imaging in different malignancies.
Recently, a 17-year-old male, with a diagnosis of papillary carcinoma of thyroid, who had undergone total thyroidectomy and radioiodine ablation 2 years previously, presented with a history of recent onset left supraclavicular adenopathy. He had no other systemic symptoms and the stimulated serum thyroglobulin level was 0.4 ng/ml. The whole body radioiodine scan was negative for any disease focus. While an excision of the palpable adenopathy was being contemplated, a whole body FDG-PET was carried out, parallel to ultrasonography of the neck, to rule out any other focus of non-iodine avid disease in the rest of the whole body.
A FDG-PET scan was completed ( Fig. 1 a and b) which found intense FDG uptake in the nodal conglomerate (SUVmax 8.96) in the left supraclavicular area and two tiny foci in the right supraclavicular area. Ultrasonography (USG) of the neck demonstrated confluent lymph nodal mass on left side at level IV and in the supraclavicular area. Also noted was 3 small subcentimeter sized nodes at right level III along jugular vein. An USG guided FNAC (ultrasonography guided fine needle aspiration cytology) smear of the nodes revealed epithelioid granuloma in necrotic background indicating granulomatous inflammation consistent with tuberculosis ( Fig. 2 ).