FDG-PET-CT, I-131-SPECT-CT, ultrasound (US) and US-guided fine needle biopsy (FNB) for recurrent differentiated thyroid cancer (DTC)

Objectives Evaluate the clinical benefit of multimodal imaging (MMI) including US-guided FNB for diagnosing recurrent DTC.

Methods 27 consecutive patients (pts.; age 58 ± 14 years; 41 % men) after previous thyroidectomy and I-131 ablation were prospectively studied between 7/2009 and 12/2010 with: (1) pre-PET neck US, (2) scintigraphy with ≥ 3 GBq I-131 incl. SPECT-CT of the neck, (3) whole body F-18-FDG PET-CT with a dedicated PET series with coregistered contast-enhanced-CT of the neck (slice thickness 1.5 mm), (4) post-PET US, (5) FNB of at least 1 index lesion. hTg, I-131 and PET were taken under endogenous or exogenous TSH-stimulation.

Results MMI was positive in 17 pts. (median hTg 16 ng/ml; range 0 - 2674) and negative in 10 (hTg 5; 0 - 86). 21 malignant lesions in the neck and mediastinum were detected in 13 pts.: 18 lymph node metastases (17/18 FDG-positive; 2 I-131-pos.; all confirmed by FNB and/or surgery) and 3 thyroid bed recurrences (all FDG-positive, I-131 negative, pos. FNB). 4 pts. had distant metastases: lung metastases in 2, bone metastases in 2, all FDG and/or I-131 positive. FDG-PET showed 8 false positive lesions: 6 inflammatory lymph nodes in 4 pts. (confirmed by FNB), 1 paralaryngeal focus (negative surgery) and pulmonary infiltrates in 1 patient (negative control CT). 1 pt. had an I-131 positive persisting pyramidal lobe. Compared with pre-PET US, MMI lead to therapeutically significant upstaging in 8 pts. (more extensive surgery in 6, radiation therapy in 1, laser ablation in 1).

Conclusions FDG-PET-CT changed therapy due to upstaging in 8/27 (30 %) of pts. False positive results in 4 pts. could be eliminated by FNB. FNB is strongly recommended as a supplement to FDG-PET in the neck.

Research Support Western Norwegian Health Care grant 91149