RAI thyroid bed uptake after total thyroidectomy: A novel SPECT‐CT anatomic classification system

Abstract

Objective Recent, more selective use of radioactive iodine (RAI) has led to reevaluation of the clinical importance of achieving complete total thyroidectomy with minimal residual normal thyroid tissue. We utilize the improved localization by post-RAI remnant ablation, single photon emission computerized tomography-computed tomography (SPECT-CT) to define specific anatomic sites of residual RAI-uptake foci after total thyroidectomy for differentiated thyroid cancer (DTC) and to provide a novel classification system relating uptake to thyroid anatomy and preservation of adjacent neural structures. Study Design Retrospective. Method Radioactive iodine-uptake foci in thyroid bed were localized by SPECT/CT imaging at the time of RAI remnant ablation in 141 DTC patients undergoing total thyroidectomy. Results Minimal residual RAI uptake (median 0.32% at 24 hours) in the thyroid bed was detected by diagnostic planar whole body scans in 93% and by posttherapy SPECT/CT imaging in 99% of subjects. Discrete RAI uptake foci were identified on the SPECT/CT imaging at Berry’s ligament (87%), at superior thyroid poles (79%), in paratracheal-lobar regions (67%), in isthmus-region (54%), and in pyramidal lobe (46%). Despite the residual foci, the nonstimulated thyroglobulin (Tg) prior to remnant ablation (with a median thyroid-stimulating hormone of 0.36 m IU/L) was <0.6 ng/mL in 53% and <1 ng/mL in 73% of cases. Conclusion After extracapsular total thyroidectomy, highly sensitive detection tools identify microscopic residual RAI avid foci in thyroid bed in the majority of patients. These foci can be classified as 1) neural-related and 2) capsule-related. These common residual foci have no relationship to postoperative Tg, suggesting that attempts at radical removal of thyroid tissue in these locations may not be warranted.

Use of radioiodine‐131 scan to measure influence of surgical discipline, practice, and volume on residual thyroid tissue after total thyroidectomy for differentiated thyroid carcinoma

“…15,16,19 Although it is well known that mortality outcomes in patients surgically managed with well-differentiated thyroid carcinoma are favorable, 6,10 the estimations surrounding recurrence are not as promising. 15,16,19 Although it is well known that mortality outcomes in patients surgically managed with well-differentiated thyroid carcinoma are favorable, 6,10 the estimations surrounding recurrence are not as promising.…”

“…15,19,20 Our study also did not attempt to correlate surgeon parameters with disease recurrence. In tertiary care centers where resident surgeons are commonly involved in procedures during their training, a resident physician may complete the majority of a case while the staff would be recorded as the operator.…”

“…First, through administration of a therapeutic dose of I-131, residual thyroid tissue is ablated and facilitates biochemical follow-up. 2,6,10,12,13,15,16 Contemporary literature illustrates differences in rates of complication after thyroidectomy, with more experienced or higher-volume surgeons producing lower rates of hypocalcemia and recurrent laryngeal nerve palsy as well as improved patient outcomes. Last, early and delayed postablation radioactive I-131 scans are able to visualize and quantify remnant thyroid tissue and to detect metastases, thus contributing to classifying and informing appropriate follow-up and interventions.…”

“…Last, early and delayed postablation radioactive I-131 scans are able to visualize and quantify remnant thyroid tissue and to detect metastases, thus contributing to classifying and informing appropriate follow-up and interventions. 15 This residual tissue is often limited to anatomically challenging locations, including the superior aspect of the pyramidal lobe or Berry's ligament. 14 Because thyroidectomies are performed by surgeons who vary broadly in their discipline, hospital setting, and procedural volume, there may be a resultant variance in the amount of postoperative remnant thyroid tissue.…”

“…1,[9][10][11][12][13] These postablation scans have been estimated to guide changes in subsequent management in up to 9%-15% of patients with thyroid cancer. 15,19,20 Because of the suboptimal morbidity and mortality outcomes of larger remnant thyroid tissue, an evaluation of the operator variables surrounding thyroidectomy may provide clinically pertinent insight. Larger remnant thyroid tissues result in less efficacious ablation, more local symptoms after radiotherapy, less accurate serum thyroglobulin (Tg) monitoring for recurrence or metastasis, and a greater likelihood of late recurrence in a middle-aged cohort with increasing longevity.…”