Positive thyroid cancer scintigraphy using technetium-99m methoxyisobutylisonitrile

Abstract

The aim of the study was to evaluate the possibility of detecting thyroid cancer recurrences without the need for withdrawal of thyroid suppressive treatment. Upper-body or whole-body scintigraphy was performed in a group of 200 patients evaluated for differentiated thyroid cancers in 1993 and 1994 using technetium-99m sestamibi. Scans were performed 20-30min following i.v. administration of 500MBq of 99mTc-methoxyisobutylisonitrile (MIBI). Bone and lung metastases were detected with very high sensitivity and specificity, with a very high predictive value of negative results and a somewhat lower predictive value of positive results. The sensitivity and specificity of findings in the neck were lower but the predictive value of negative results was high. Whole-body scans with 99mTc-MIBI are a useful tool in the follow-up of patients with differentiated thyroid cancer, for the detection of distant metastatic lesions.

Diagnostic Value of Technetium-99m Methoxyisobutyl Isonitrile (99mTc-MIBI) Scintigraphy in Detecting Thyroid Cancer Metastases: A Critical Evaluation

“…Another factor for their low sensitivity might be the delayed image acquisition time, because we previously found that 99mTc-MIBI accumulation observed in the early image (10-30 minutes) disappeared at the delayed scan (3 hours) in 8 of 13 patients with lung métastases and 5 of 11 bone metastases (14). However, Nemec et al (12) reported high sensitivity for bone (100%; 17/17) and lung (94.7%; 18/19) Compared with the studies by Nemec et al (12), we had lower sensitivity (78.4%; 40/51) for lung métastases, which appears attributable to the small size of lesions (<1.0 cm).…”

“…Because 99mTc-MIBI enters skeletal muscle tissue by passive diffusion, muscle perfusion abnormalities such as peripheral artery disease (20), muscle diseases, and removal of muscles after extensive operation for thyroid cancer may cause asymmetric appearance and also false-positive scans. Nemec et al (12) reported 39 false-positive sites including 27 in the neck, 9 in the lung, and 3 in the bone, and suggested that false-positive uptake may have occurred in scars after previous treatment of primary tumors and their métastases. However, they did not describe other causes of false-positive results.…”

“…As a nonspecific tumor-seeking agent not dependent on tissue type, its use has been proposed in detecting a variety of malignant neoplasms and their metastasis (4)(5)(6)(7)(8). With regard to thyroid cancer, 99mTc-MIBI has also been reported to localize the métastases successfully (9)(10)(11)(12)(13)(14), although its ability to differentiate primary malignant from benign tumors is limited (13,15). 99mTc-MIBI accumulates within cell mitochondria and cytoplasm through electrical potentials generated across membrane bilayers (6).…”

“…In both studies, the data were analyzed on a patient basis, not on a lesion basis. Moreover, Nemec et al(12) did not perform WBS in all patients, which makes the diagnosis of true-negative lesions quite difficult.…”

Nuclear Imaging in the Management of Thyroid Carcinoma

“…The precise role of this agent in assessing patients with thyroid cancer has yet to be determined. Available evidence indicates that, like 201T1, 99mjc sestamibi may be useful in localizing recurrent thyroid carcinoma in 131I-negative patients in whom there is other evidence of recurrence (47)(48)(49)(50). Because of the 6-h half-life of 99mTc, allowing the administration of 20-25 mCi (740-925 MBq), and its more suitable photon energy for imaging, 99mTc sestamibi produces images of higher quality than 201T1.…”