Number of Foci of Functioning Thyroid Tissue Remaining after Thyroidectomy for Differentiated Thyroid Cancer: Institutional Experience.

Radioiodine imaging of the neck with a pinhole collimator (PinC) is frequently performed in differentiated thyroid cancer (DTC) patients for visualizing individual, and a total number of foci (NOF) of functioning residual thyroid tissue (FRTT) within the thyroid bed in postthyroidectomy patients. The objective of this study was to determine our experience regarding the NOF of FRTT visualized on pretherapy radioiodine PinC images. We performed a retrospective review of radioiodine PinC images of the neck of patients with very low-risk DTC and who had thyroidectomy performed by selected surgeons at MedStar Washington Hospital Center. For each patient's image, the NOF of FRTT was determined by two blind readers. Statistical analysis was performed. One hundred and twenty-six patients met the criteria. Surgeon (S1, S2, S3, and S4) performed 17, 10, 86, and 13 thyroidectomies, respectively. The analysis (mean, range, and standard deviation) of NOF of FRTT was: S1: (2.2, 0-5, 1.3); S2: (1.6, 1-3, 0.8); S3: (2.6, 0-7, 1.5); S4: (3.3, 1-5, 1.3). The percentages of < 2, ≤3, ≤4, and <5 foci remaining were 4.9%, 21.5%, 77.0%, and 91.3%, respectively. For the selected surgeons, the NOF of FRTT in the thyroid bed or neck in postthyroidectomy patients never exceeded 7, rarely exceeded 5 (2.4%), and infrequently exceeded 4 (8.7%). Based on these data, our thresholds of the NOF for which we perform further workup for possible locoregional disease are ≥5. Each facility is encouraged to establish their own criteria for their facility and preferably for each of their surgeons.