False Positive Findings on I-131 WBS and SPECT/CT in Patients with History of Thyroid Cancer: Case Series

Abstract

Introduction. Although whole body scan (WBS) with I-131 is a highly sensitive tool for detecting normal thyroid tissue and metastasis of differentiated thyroid cancer (DTC), it is not specific. Additional information, provided by single photon emission computed tomography combined with X-ray computed tomography (SPECT/CT) and by the serum thyroglobulin level, is extremely useful for the interpretation of findings. Case Presentation. We report four cases of false positive WBS in patients with DTC: ovarian uptake corresponding to an endometrioma, scrotal uptake due to a spermatocele, rib-cage uptake due to an old fracture, and hepatic and renal uptake secondary to a granuloma and simple cyst, respectively. Conclusions. Trapping, organification, and storage of iodine are more prominent in thyroid tissue but not specific. Physiologic sodium-iodine symporter expression in other tissues explains some, but not all, of the WBS false positive cases. Other proposed etiologies are accumulation of radioiodine in inflamed organs, metabolism of radiodinated thyroid hormone, presence of radioiodine in body fluids, and contamination. In our cases nonthyroidal pathologies were suspected since the imaging findings were not corroborated by an elevated thyroglobulin level, which is considered a reliable tumor marker for most well-differentiated thyroid cancers. Clinicians should be aware of the potential pitfalls of WBS in DTC to avoid incorrect management.

Inguinal Endometriosis Visualized on I-131 Whole Body Scan

“…An increase in blood flow to the inguinal endometriosis or presence of inflammation in this area might be the reasons for increased radioiodine uptake. Hyperemia, vasodilation, local edema, and increased capillary permeability may cause increased radioiodine uptake in inflamed areas (7,8). In our case, there were multiple reactive lymph nodes around the inguinal mass.…”

False-positive radioiodine uptake after radioiodine treatment in differentiated thyroid cancer

“…Overall, the literature showed 145 case reports and two series regarding false-positive 131 uptake after RIT For the reasons stated above, we excluded 129 papers, considering only those in which SPECT/CT was performed. A total of 18 papers were thus included: 1 series [17] and 17 case reports [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. The series reported 23 cases of falsepositive results: 15 in the chest, six in the pelvis, one in the cranium, and one in the abdomen.…”

“…Overall, 20 cases regarded radioiodine uptake in the chest: 11 in the lung (mainly inflammatory), four on the chest bones or on soft tissue due to inflammation/trauma, one in the thymus, one mesenchymal tumor and the rest in not well-characterized sites [17][18][19][20][21]34]. A total of 15 cases regarded uptake in the abdomen/pelvis: six in the kidney (cysts), five in the ovary (teratoma, benign cysts and malignant disease), two in the uterus and the others in not well-characterized sites [22][23][24][25][26][27][28][29]. Three cases reported uptake in the head: two surgical clips, and one on one eye [30,31,33].…”

False-positive radioiodine accumulation in a huge pelvic mass after thyroidectomy for papillary carcinoma, a case report from Syria

“…Lungo M et al [ 5 ] and Hannoush et al [ 6 ] in 2000 and 2017 reported a false-positive radioiodine uptake in endometrial cyst. Benign cystadenofibroma was reported by Flug J et al [ 7 ].…”