I-131 uptake in fat necrosis of the breast

Radioiodine whole body scan pitfalls in differentiated thyroid cancer

PURPOSE

whole body scan (WBS) performed following diagnostic or therapeutic administration of I-131 is useful in patients with differentiated thyroid carcinoma. However, it can be falsely positive in various circumstances. We aimed to report a series of pitfalls in a clinical perspective.

METHODS

A search in the database PubMed utilizing the following terms: "false radioiodine uptake" and "false positive iodine 131 scan" has been made in January 2023. Among the 346 studies screened, 230 were included in this review, with a total of 370 cases collected. Physiological uptakes were excluded. For each patient, sex, age, dose of I-131 administered, region and specific organ of uptake and cause of false uptake were evaluated.

RESULTS

370 cases of false radioiodine uptake were reported, 19.1% in the head-neck region, 34.2% in the chest, 14.8% in the abdomen, 20.8% in the pelvis, and 11.1% in the soft tissues and skeletal system. The origin of false radioiodine uptake was referred to non-tumoral diseases in 205/370 cases (55.1%), benign tumors in 108/370 cases (29.5%), malignant tumors in 25/370 cases (6.7%), and other causes in 32/370 cases (8.7%).

CONCLUSIONS

WBS is useful in the follow-up of patients with differentiated thyroid carcinoma, however it can be falsely positive in various circumstances. For this reason, it is critically important to correlate the scintigraphic result with patient's medical history, serum thyroglobulin levels, additional imaging studies and cytologic and/or histologic result.

False-Positive 131I Uptake After Transareola Endoscopic Thyroidectomy in a Patient With Papillary Thyroid Carcinoma

ABSTRACT

False-positive 131I accumulation in patients with thyroid carcinoma could be due to various etiologies. Herein, we reported a case of papillary thyroid carcinoma in a 36-year-old woman. She underwent a 131I radiotherapy after a transareola endoscopic total thyroidectomy. 131I scintigraphy showed a high uptake in the thyroid bed. Surprisingly, increased activity was also noted in the right areola area. This activity corresponding to the entry site of endoscope revealed on the following SPECT/CT.

Dosing Therapeutic Radiopharmaceuticals in Obese Patients

The prevalence of obesity has increased dramatically in the Western population. Obesity is known to influence not only the proportion of adipose tissue but also physiological processes that could alter drug pharmacokinetics. Yet, there are no specific dosing recommendations for radiopharmaceuticals in this patient population. This could potentially lead to underdosing and thus suboptimal treatment in obese patients, while it could also lead to drug toxicity due to high levels of radioactivity. In this review, relevant literature is summarized on radiopharmaceutical dosing and pharmacokinetic properties, and we aimed to translate these data into practical guidelines for dosing of radiopharmaceuticals in obese patients. For radium-223, dosing in obese patients is well established. Furthermore, for samarium-153-ethylenediaminetetramethylene (EDTMP), dose-escalation studies show that the maximum tolerated dose will probably not be reached in obese patients when dosing on MBq/kg. On the other hand, there is insufficient evidence to support dose recommendations in obese patients for rhenium-168-hydroxyethylidene diphosphonate (HEDP), sodium iodide-131, iodide 131-metaiodobenzylguanidine (MIBG), lutetium-177-dotatate, and lutetium-177-prostate-specific membrane antigen (PSMA). From a pharmacokinetic perspective, fixed dosing may be appropriate for these drugs. More research into obese patient populations is needed, especially in the light of increasing prevalence of obesity worldwide.

Solitary Breast Metastasis From Thyroid Papillary Carcinoma Revealed on Whole-Body Radioactive 131I Scan

Breast metastasis from thyroid papillary carcinoma is an exceptional situation. Here, we present the diagnostic approach and the management of a 19-year-old woman with single breast metastasis from thyroid carcinoma. There was no extra thyroidal extension, neoplastic emboli, or lymph node invasion. The metastasis was revealed by whole-body radioactive I scan, explored by a fine-needle aspiration, and confirmed by elevated thyroglobulin in situ.

Management of Incidental Breast Lesions Detected at Nuclear Medicine Examinations

Nuclear medicine studies are often performed in patients with breast cancer; however, incidental radiotracer uptake in the breasts can be observed in patients with nonbreast malignancies. Benign and malignant lesions can be identified on planar, SPECT, and PET scans. This review will outline the molecular and radiographic imaging appearance of benign and malignant breast lesions on sestamibi scans, bone scans, radioiodine studies, as well as PET studies using fluorine 18 (¹⁸F) fluorodeoxyglucose, gallium 68 (⁶⁸Ga) tetraazacyclododecane tetraacetic acid octreotate (or DOTATATE), ⁶⁸Ga prostate-specific membrane antigen, and ¹⁸F-fluciclovine radiotracers. Recognizing these lesions at molecular and anatomic imaging is important to ensure accurate diagnosis and appropriate management. Keywords: Breast, Mammography, Molecular Imaging, PET/CT, Radionuclide Studies, SPECT/CT © RSNA, 2020.

I-131 uptake in the breast from fat necrosis

Radioactive iodine I-131 whole-body scintigraphy is used to monitor thyroid cancer metastases after total thyroidectomy. We present a case of a woman who was diagnosed with papillary thyroid cancer and underwent a total thyroidectomy. I-131 scintigraphy revealed abnormal accumulation of radioactive iodine in the right breast causing concern for thyroid cancer metastasis. Mammographic studies confirmed that the abnormal radiotracer accumulation was due to fat necrosis in the breast. I-131 uptake in fat necrosis is a poorly understood process that is not clearly defined in the literature. This case highlights that false-positive uptake of I-131 can mimic metastases of thyroid carcinoma.

Unusual Sites of Metastatic and Benign I 131 Uptake in Patients with Differentiated Thyroid Carcinoma

INTRODUCTION

Differentiated thyroid carcinoma (DTC) is the most common pathological type of thyroid carcinoma, which includes papillary and follicular subtypes. DTC is usually indolent, characterized by good prognosis, and long-term survival. Total thyroidectomy is the mainstay of treatment in DTC which is followed by diagnostic whole body 131I (WBI) scan. Like other primary malignancies of the head and neck, DTC follows a consistent pattern of spread in the cervical LNs. The central compartment, level VI and VII, is the first sentinel node followed by spread to the lateral compartments levels II-V, followed by the contralateral side. Inspite of nodal involvement, DTC usually have a favourable outcome. Presence of extrapulmonary distant metastases could predict a poor prognosis for high-dose ¹³¹I therapy. However, distant metastasis occurs often as a grave event and mortality rates vary depending on metastatic sites.

AIM AND OBJECTIVES

A range of rare ¹³¹I concentrating DTC deposits in sella, orbit, choroid, skeletal muscles, liver, skin, costochondral soft tissue, pancreas and kidney, and a few benign ¹³¹I concentrating sites are being depicted.

MATERIALS AND METHODS

Metastatic sites from DTC can be easily identified by performing a whole body ¹³¹I (WBI) scan along with a stimulated thyroglobulin (Tg) estimation (TSH >30 uIU/ml). Apart from thyroid and thyroid-related diseases, certain benign non-thyroidal pathologies can concentrate radioiodine (¹³¹I). From 13,000 of our patients who underwent radioiodine scan for thyroid cancer, we have selected a few cases of ¹³¹I concentrating benign and malignant lesions for illustration.

RESULTS

Out of 13000 DTC patients who underwent whole body ¹³¹I scintigraphy in our department from Jan 2007 till Mar 2018, 25 patients revealed benign sites of ¹³¹I uptake. 61 % patients had residual thyroid tissue with or without associated nodal involvement. Remaining patients had distant metastases. Rare sites of functioning thyroid metastases and benign sites of I 131 uptake have been selected for illustration.

CONCLUSION

Apart from the WBI (two-dimensional, planar) images, single-photon emission computed tomography-computed tomography (SPECT-CT) has been incremental in localizing benign lesions which greatly depends on their location. This pictorial review highlights the need to create an awareness to detect metastatic deposits of DTC at unexpected sites. Otherwise patients will need further investigation to rule out unsuspected sites of functioning distant metastases.