Incidental finding of a dermoid cyst in a whole-body iodine scan: importance of using [131I]SPECT/CT in the differentiated thyroid carcinoma

Abstract

A 33-year-old female with a history of total thyroidectomy for papillary thyroid carcinoma was referred to the nuclear medicine department for ablative radioiodine therapy. Post ablation scan showed an area of intense iodine uptake on the left side of the pelvic region, corresponding to the large well-defined heterogeneous mass in the left ovary in the SPECT/CT images. The radiologic features of this lesion were compatible with a dermoid cyst, previously unrecognized. Eventually, the lesion was laparoscopically removed, and a typical dermoid cyst was confirmed through histopathologic assessment.

Epidermal Cyst Mimicking Thyroid Cancer Metastasis

“…The cases of false-positive uptakes in cysts have been reported in the literature, including renal cyst, 3,4 bronchogenic cyst, 5 pleuropericardial cyst, 6 ganglion cyst, 7 sebaceous cyst, 8 benign epithelial cyst in the mesenteric fat of the abdomen, 9 and dermoid cyst of the ovary. 10 However, it is rare to observe radioiodine uptake in the epidermal cyst. In addition, this patient's axillary lesion is easily mistaken for axillary lymph node metastasis from thyroid carcinoma, because axillary lymph node metastasis is not uncommon.…”

“…False-positive on 131 I-WBS is common. The cases of false-positive uptakes in cysts have been reported in the literature, including renal cyst, 3,4 bronchogenic cyst, 5 pleuropericardial cyst, 6 ganglion cyst, 7 sebaceous cyst, 8 benign epithelial cyst in the mesenteric fat of the abdomen, 9 and dermoid cyst of the ovary 10 . However, it is rare to observe radioiodine uptake in the epidermal cyst.…”

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].…”

“…However in all cases, diagnosis was possible by SPECT/CT and other imaging techniques. In four cases [17,[22][23][24], all were in the pelvis, diagnosis was virtually impossible, and surgery had to be performed to clarify the histology. Table 1 reports the possible causes of false-positive imaging, possible sites in SPECT/CT, and possible actions for reaching a diagnosis.…”