99mTc-MIBI SPECT/CT improves identification of benign renal masses

The ability to differentiate renal cell carcinoma (RCC) from benign renal tumors can be challenging for radiologists. Without a definitive diagnosis from diagnostic imaging exams, solid renal lesions with suspicious features on contrast-enhanced computed tomography (CT) and magnetic resonance imaging (MRI) require surgery. The addition of technetium (99mTc) sestamibi single photon emission computed tomography (SPECT/CT) can improve characterization of benign tumors, say researchers at Johns Hopkins University School of Medicine in Baltimore, MD.

Renal masses are increasingly being identified, often as incidental findings, in advanced cross-sectional abdominal imaging. Without a confident diagnosis that a renal mass is benign, rates of unnecessary surgery have increased, affecting the safety of patients and increasing the costs of inappropriate healthcare treatment. Up to 20% of renal masses treated with partial or radical nephrectomy are benign, almost half being oncocytomas.

In view of this published data, principal investigator Mehrbod S. Javadi, MD, assistant professor of radiology and radiological science, and colleagues conducted a study to determine if the addition of a preoperative^99mTc-MIBI SPECT/CT exam could increase the degree of diagnostic confidence in differentiation of benign from malignant masses. They retrospectively analyzed imaging exams of 48 patients diagnosed with a solitary solid enhancing clinical T1 renal mass 7 cm or less in dimension. Malignant renal tumors were pathologically confirmed in 39 of the patients.

The patient cohort included 35 patients who had a CT exam, 12 patients a contrast-enhanced MRI, and one patient a MRI without contrast. This was followed within 8 weeks with a^99mTc-MIBI SPECT/CT scan (Symbia, Siemens). Two nuclear medicine specialists each independently interpreted the SPECT/CT scans twice, with a 10 day interval following the first interpretation. They were asked to measure the maximum^99mTc-MIBI radiotracer uptakes within the tumor and within the ipsilateral normal renal parenchyma. Two body imaging specialists interpreted the renal masses on CT and MRI examinations as malignant, indeterminate, or benign. They then were given the opportunity to review the^99mTc-MIBI SPECT/CT average uptake ratio and make a change to their rating.

The authors reported that the additional data from the^99mTc-MIBI SPECT/CT examinations improved interpreting radiologists’ confidence in 14 of the 48 lesions, or nearly 30% of the cases. Confidence level toward making a diagnosis of malignancy also increased in 5 cases. Adding the results of the uptake ratio to the cross-sectional CT or MRI analysis allowed for the identification of 77.8% benign lesions and half of the chromophobe RCCs.

“With the dramatic increase in the detection of clinically occult renal masses due to the growing use of abdominal imaging, implementation of an effective risk-adopted approach is essential to avoid over-treatment by identifying the tumors with slow growth rates that will not cause future symptoms or effect life expectancy,” the authors wrote. They recommend future studies with a larger sample size to define the performance characteristics as well as the cost effectiveness of adding^99mTc-MIBI SPECT/CT exams to a patient’s orders.

REFERENCE

1. Sheikhbahaei S, Jones CS, Porter KK, et al. Defining the Added Value of^99mTc-MIBI SPECT/CT to Conventional Cross-Sectional Imaging in the Chaacterization of Enhancing Solid Renal Masses. Clin Nucl Med. 2017 42; 4: e188-e193.