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.
Keywords
Differentiated thyroid cancer - number of foci - pinhole imaging - postthyroidectomy
- thyroid tissue
