Adding 99mTc-MIBI SPECT CT imaging improves accuracy, confidence in diagnosing renal carcinoma

By Liz Meszaros, MDLinx
Published April 21, 2017

Key Takeaways

Preoperative 99mTc-sestamibi single-photon emission computed tomography/computed tomography (99mTc-MIBI SPECT/CT) may strengthen results obtained with conventional imaging—including CT and MRI—in patients with clinical stage T1 solid renal masses, by both improving benign histology characterization and lowering the possibility of misclassification, according to a recent study published in the journal Clinical Nuclear Medicine.

“Sestamibi SPECT/CT lets radiologists and urologists ‘see’ the most common benign kidney tumor, something CT and MRI have not succeeded in doing alone,” said study co-author Mohamad E. Allaf, MD, MEA Endowed Professor of Urology, Johns Hopkins University School of Medicine, Baltimore, MD. “This noninvasive scan may prevent patients with a potentially benign kidney tumor from having to undergo a surgery to remove the tumor or potentially the entire kidney, along with its associated risks and high costs. At Johns Hopkins, use of this test has already spared a number of our patients from unnecessary surgery and unnecessary removal of a kidney that would require them to be on dialysis. These results are hugely encouraging, but we need to do more studies.”

Conventional imaging with CT or MRI has, traditionally, frustrated clinicians with an inability to distinguish benign from malignant kidney tumors.

“In the absence of diagnostic certainty, surgeons tend to remove kidney tumors in an abundance of caution, leading to an estimated 5,600 surgically removed benign kidney tumors each year in the United States,” said Michael A. Gorin, MD, one of two residents involved in developing this approach, and now chief resident, The James Buchanan Brady Urological Institute, Johns Hopkins University School of Medicine, Baltimore, MD.

Drs. Allaf and Gorin and fellow researchers conducted this study to assess whether adding preoperative 99mTc-MIBI SPECT/CT increased diagnostic confidence in differentiating benign from malignant enhancing renal masses. They enrolled 48 patients with clinical stage T1 solid renal masses, all of whom underwent 99mTc-MIBI SPECT/CT before partial or radical nephrectomy. They also retrospectively gathered conventional CT and MRI images, performed roughly 8 weeks before the 99mTc-MIBI imaging.

Both before and after reviewing the 99MTc-MIBI uptake ratios for each patient, two blinded readers recorded their degree of confidence in the classification of each lesion with conventional imaging based on a 5-point scale, with 1 equal to definitely benign, and 5 to definitely malignant. The reference standard was surgical pathology.

These researchers found that the added review of the 99mTc-MIBI SPECT/CT uptake ratios increased the diagnostic confidence in the differentiation of solid renal masses in 29.2% of the lesions. Furthermore, in nine lesions, adding 99mTc-MIBI SPECT/CT changed initial confidence levels of malignancy to a benign diagnosis.

A diagnosis of a benign histology was confirmed via post-surgical pathology in seven lesions, and one of chromophobe renal cell carcinoma in two lesions. In five cases, 99mTc-MIBI increased the confidence level toward malignancy, and all were confirmed as renal cell carcinoma upon surgical pathology. Area under the receiver operator curve was 0.60 for conventional imaging alone, and 0.85 after 99mTc-MIBI SPECT/CT review (P for difference=0.03).

Researchers noted that even in patients in whom tumors were not reclassified, adding 99mTc-MIBI SPECT/CT increased the physicians’ ability to more confidently classify malignant tumors, thus reducing the risk of misdiagnosis and unnecessary surgery for all patients.

“As radiologists, we have struggled to find noninvasive ways to better classify patients and spare unnecessary surgery, but this has not been easy,” said Steven P. Rowe, MD, PhD, the second of the two former residents who developed this approach, and now assistant professor of radiology and radiological science, Johns Hopkins University School of Medicine. “Sestamibi SPECT/CT offers an inexpensive and widely available means of better characterizing kidney tumors, and the identical test is now being performed as part of a large trial in Sweden, for which the first results have just recently been published and appear to confirm our conclusions.”

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