Initial experience using 99mTc-MIBI SPECT/CT for the differentiation of oncocytoma from renal cell carcinoma

Abstract

Purpose: The differentiation of oncocytoma from renal cell carcinoma (RCC) remains a challenge with currently available cross-sectional imaging techniques. As a result, a large number of patients harboring a benign oncocytoma undergo unnecessary surgical resection. In this study, we explored the utility of 99mTc-MIBI SPECT/CT for the differentiation of these tumors based on the hypothesis that the large number of mitochondria in oncocytomas would lead to increased 99mTc-MIBI uptake.

Patients and methods: In total, 6 patients (3 with oncocytoma and 3 with RCC) were imaged with 99mTc-MIBI SPECT/CT. Relative quantification was performed by measuring tumor-to-normal renal parenchyma background ratios.

Results: All 3 oncocytomas demonstrated radiotracer uptake near or above the normal renal parenchymal uptake (range of uptake ratios, 0.85-1.78). In contrast, the 3 RCCs were profoundly photopenic relative to renal background (range of uptake ratios, 0.21-0.31).

Conclusions: 99mTc-MIBI SPECT/CT appears to be of value in scintigraphically distinguishing benign renal oncocytoma from RCC.

FIGURE 1

Line-block diagram of the imaging protocol used to obtain the planar, SPECT, and SPECT/CT images.

FIGURE 2

A, One-minute postinjection posterior dynamic planar image of patient 1 demonstrating a subtle photopenic defect in the cortex of the upper pole of the right kidney at the site of the patient’s known oncocytoma (arrowhead). The patient was status post-left nephrectomy, hence the lack of visualization of the left kidney. B, Thirty-minute postinjection posterior dynamic planar image of the same patient. There has been fill-in of the large right upper pole oncocytoma (arrowhead) with relative retention of radiotracer in the mass higher than that in the surrounding normal renal parenchyma.

FIGURE 3

Representative images of the oncocytomas included in this study. A, Axial contrast-enhanced CT, axial SPECT (B), and axial SPECT/CT fusion images of a right upper pole oncocytoma (C) with a representative histologic image (D, hematoxylin and eosin stain [HE] ×20) (patient 1, white and black arrowheads). E, Axial contrast-enhanced T1-weighted MRI, axial SPECT (F), and axial SPECT/CT fusion images of a right medial interpolar oncocytoma (G) with an accompanying histologic image (H, HE ×20) (patient 2, white and black arrowheads). I, Coronal contrast-enhanced CT, coronal SPECT (J), and coronal SPECT/CT fusion images of a right lower pole oncocytoma (K) with a corresponding histologic image (L, HE ×20) (patient 3, white and black arrowheads).

FIGURE 4

Representative images of the RCCs included in this study. A, Coronal contrast-enhanced CT, coronal SPECT (B), and coronal SPECT/CT fusion images of a left upper pole Fuhrman grade III clear cell RCC (C) with a representative histologic image (D, HE ×20) (patient 4, white and black arrowheads). E, Axial contrast-enhanced CT, axial SPECT (F), and axial SPECT/CT fusion images of a medial left lower pole unclassified RCC (G) with a corresponding histologic image (H, HE ×20) (patient 5, white and black arrowheads). I, Axial contrast-enhanced CT, axial SPECT (J), and axial SPECT/CT fusion images of an Xp11 translocation RCC (K) with a histologic image (L, HE ×20) (patient 6, white and black arrowheads).