Introduction: Initial studies on 99mTc-Sestamibi Single Photon Emission Computed Tomography/Computed Tomography (SPECT/CT) on small renal masses (SMR) suggested its use to characterize renal oncocytoma (RO) from renal cell carcinoma (RCC). In this case series, we present the initial cases managed at our tertiary referral center. Methods: We prospectively collected data on 40 consecutive patients with a SMR diagnosed at our institution and submitted to 99mTc- SPECT/CT at our Institution between May 2021 and September 2022. Of all, pathological data, either from biopsy or surgery, are available for 25 patients. We assessed the sensitivity (SE), specificity (SP), positive predictive value (PPV), negative predictive value (NPP) and the diagnostic accuracy (through the Area Under the roc Curve - AUC) of the 99mTc- SPECT/CT to differentiate oncocytoma and benign renal masses from malignant ones. Results: Of 25 patients, 7 (28%) were females and 18 (72%) males. Median age at diagnosis was 64.9 (95%CI 57.1-72.1). Median max diameter at imaging was 3 cm (IQR 2.6-3.3). The SMR was diagnosed in 2 cases with the solely MRI (8%), in 12 cases with a CT scan (48%) and in 11 with both (44%). In 7 cases the SMR resulted positive at the 99mTc- SPECT/CT scan, suggesting a high-density mitochondrial tissue. 10 cases were submitted to biopsy and 15 to robotic partial nephrectomy. Of 10 biopsies, 2 SMRs were also treated with ablation and 1 which resulted positive for clear cell (cc)RCC was submitted to active surveillance. Overall, there were 9 oncocytomas, 8 ccRCC, 6 papillary tumors (of which 1 type I and 3 type II), 1 chronic nephritis and 1 cystic lesion with low probability of malignancy. Overall, for oncocytomas, SE was 55.5%, SP 87.5%, PPV 71.4% and NPV 77.8. The accuracy in differentiating oncocytomas from SMR of other nature was 74.6%. Considering all kind of benign SMRs, SE was 50%, SP 86.7%, PPV 71.4% and NPV 72.2%. The accuracy in differentiating benign from malignant SMR was 71.8%. Conclusions: Despite the relatively small sample size and the initial experience, 99mTc- SPECT/CT should be regarded as a promising, non-invasive technique with good accuracy in the detection of renal oncocytoma. SOURCE OF Funding: None
