Majority of the renal masses are now detected when they are asymptomatic and small and the management depends on accurate characterization of the mass. Although imaging can be used to diagnose these masses, some are incorrectly believed to be renal cell carcinoma and unnecessary surgery may be performed. Multiple studies demonstrate that between 8- 27% of surgically resected solid renal masses are benign. In a large study by Jae Heon Kim, the overall prevalence of benign pathologic findings after Partial Nephrectomy exceeded 30%.(1)
Renal MIBI scan can be used for characterization of small renal masses and also for differentiation of oncocytomas and hybrid oncocytic/ chromophobe tumors (HOCTs) from other renal tumor histologies.
The basis of the 99mTc-sestamibi scan is that oncocytomas and HOCTs have high radiotracer uptake, whereas RCCs have low uptake. Normal renal parenchyma also demonstrates high avidity for 99mTc-sestamibi so common pattern seen with oncocytomas is uptake similar to the surrounding parenchyma. In contrast, RCCs typically have lower uptake relative to surrounding parenchyma appearing as photopenic “punched out” lesions or defects on the SPECT image.
P Viswambaram investigated 74 patients with SRMs with 99mTc-sestamibi SPECT/CT which correctly identified 49 malignant tumours and 11 benign tumours, resulting in a sensitivity of 89% and specificity of 0.73%.(2) In systemic review by Basile et al, Sestamibi SPECT/CT showed overall sensitivity of 86% and specificity of 91% in the differentiation of benign and malignant renal masses.(3) However, Sestamibi SPECT showed low specificity in differentiating oncocytomas and HOCT from chRCC (~41%). Finally, sestamibi SPECT/CT can be used to avoid overtreatment in patients with multiple synchronous renal tumors with indications for nephron-sparing surgery.
Figure 1: Sestamibi scan showing renal mass and surgical specimen
By Dr Ankit Sachan, Safai Medical College, UP
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