The Evaluation Of Abnormal Radioiodine Uptake Foci On Neck Diagnostic ¹³¹I-SPECT/CT In Differentiated Thyroid Cancer

Background:Differentiated thyroid carcinoma（DTC）is the most common type of thyroid malignancy,accounting for over 90%of all cases.Current treatments for DTC include thyroidectomy,radioactive iodine-131 therapy,and thyroid-stimulating hormone（TSH）suppression therapy.According to guidelines,patients undergoing DTC surgery should have as much thyroid tissue removed as possible to clear all visible thyroid tissue.However,to avoid postoperative complications,surgeons may conservatively remove thyroid tissue,resulting in residual tissue.Accurately assessing postoperative residual thyroid tissue can play an important role in formulating subsequent iodine-131 therapy plans,reducing disease recurrence and metastasis.The diagnostic iodine-131 scan includes iodine-131 whole body scan(¹³¹I-WBS)and iodine-131 single-photon emission computed tomography/computed tomography(¹³¹I-SPECT/CT).¹³¹I-WBS has gradually become the preferred imaging modality for detecting residual thyroid tissue due to its ease of use and high sensitivity.However,WBS cannot accurately locate abnormal uptake areas.¹³¹I-SPECT/CT can further improve the accuracy of abnormal uptake localization without invasion,precisely evaluating the location,uptake level,and imaging characteristics of abnormal uptake areas in the neck.Although there are many reports on the value of ¹³¹I-WBS and¹³¹I-SPECT/CT in detecting postoperative iodine-131 uptake areas in DTC,research on the location and imaging features of abnormal iodine-131 uptake areas after DTC surgery is rare and has not been systematically summarized,especially when the abnormal iodine-131 accumulation lesions are located outside the thyroid bed area,their clinical significance remains unclear and requires further analysis and research.Objective:This study aims to evaluate the distribution characteristics and imaging features of abnormal radioiodine uptake foci on neck diagnostic ¹³¹I-SPECT/CT in patients with differentiated thyroid carcinoma after thyroidectomy,as well as their clinical significance for decision-making.Methods:81 postoperative patients with differentiated thyroid carcinoma who underwent total thyroidectomy were included in this study.The neck abnormal iodine-131 uptake areas on diagnostic ¹³¹I-SPECT/CT images were analyzed by comparing them with preoperative computed tomography（CT）images.Based on the preoperative distribution of the thyroid on CT,the location of the uptake areas was divided into two parts:within the thyroid bed area and outside the thyroid bed area.According to CT structural imaging,the uptake areas were classified as negative,suspicious,or positive,and according to the iodine uptake characteristics on SPECT,the uptake areas were classified as high,moderate,or low uptake.The uptake areas within the thyroid bed area were further divided into five regions based on their anatomical location.And the location,uptake level,and CT appearance of residual lesions in each region were analyzed and categorized into normal and abnormal CT groups.The abnormal iodine-131 uptake areas outside the thyroid bed area were classified as ectopic thyroid tissue,lymph node metastasis,or undetermined lesions,and their location,uptake level,and CT appearance were analyzed.General information（age and gender）,clinical information（T stage,N stage,M stage,primary lesion scope,pathological type,thyroid function test indicators,BRAF-V600E gene mutation）,and iodine-131uptake area imaging information（number,location,uptake level,CT appearance）of all cases were collected and analyzed.The effective risk factors for residual thyroid lesions were analyzed using chi-square tests.Results:Of the 81 patients,79（97.5%）had 179 abnormal iodine-131 uptake areas,with111 within the thyroid bed area and 68 outside of it.Of the 111 uptake areas within the thyroid bed area,57（51.4%）were considered to be residual thyroid lesions mainly located in region I（57,51.4%）,followed by regions III（26,23.4%）and II（20,18.0%）.Most of them showed a suspicious or positive CT appearance（58,52.3%）,while high uptake was observed in most on SPECT images（60,45.1%）.Chi-square tests revealed that involvement of bilateral primary lesions and T3-4 staging were effective risk factors for CT abnormalities（suspicious and/or positive）（χ²=6.280,P=0.012;χ²=5.229,P=0.022）,while other variables（age,gender,pathological type,NM staging,stimulated thyroglobulin,stimulated thyroid-stimulating hormone,thyroglobulin antibody,BRAF-V600E gene）were not significant risk factors.Of the abnormal iodine-131 uptake areas outside the thyroid bed area,41（60.2%）were ectopic thyroid tissue,14（20.6%）were lymph node metastases,and 13（19.1%）were undetermined lesions.Conclusion:The incidence of abnormal iodine uptake foci in the neck after surgery is high（97.5%）in DTC patients,with certain distribution and imaging characteristics on diagnostic ¹³¹I-SPECT/CT.The incidence of residual lesions in the thyroid bed area after surgery is also high（84.0%）in DTC patients,mainly located beside the tracheal cartilage.This suggests that more precise removal of thyroid tissue around the tracheal cartilage is needed during surgery to prevent damage to surrounding tissues.Bilateral involvement of the primary lesion and T3-4 stage are effective influencing factors for abnormal CT findings of residual thyroid tissue.For these patients,the quality of surgical clearance should be improved to reduce the occurrence of visible residual lesions.When dealing with iodine uptake foci outside the thyroid bed area,it is important to differentiate between ectopic thyroid tissue and lymph node metastasis.Some iodine uptake foci outside the thyroid bed area have yet to be characterized,with a reported incidence of approximately 16.1%that has not been documented in domestic or foreign literature.