A 65 year old man presents with an incidentally noted right renal mass.
The patient underwent additional imaging and below is the raw SPECT data. What radiotracer is being used? How can this information assist in the characterization of this mass?
This is a patient with a renal oncocytoma. The Tc99m sestamibi imaging shows uptake equal or greater than renal parenchyma in the mass. The patient had a renal biopsy showing an oncocytic neoplasm, and this imaging study has allowed the patient to be followed rather than undergo a nephrectomy.
Compare this case to another patient with an incidental renal mass:
In this second case, the renal sestamibi scan shows absent radiotracer uptake:
This second patient underwent nephrectomy revealing clear cell renal carcinoma.
An evolving area of research, there is growing evidence that Tc99m sestamibi uptake in renal tumors is strongly correlated with a benign histology- either oncocytoma or hybric oncocytic/chromophobe tumors. Level of uptake in these tumors is nearly equal or greater than that of normal renal parenchyma (at least 60% as intense), while renal cell carcinoma typically has absent or markedly decreased uptake relative to the parenchyma.
This imaging characterization is especially beneficial given that these benign and malignant renal masses cannot be differentiated by contrast enhanced CT or MRI. Renal biopsy also frequently cannot differentiate these lesions, with a relatively high nondiagnostic rate.
References:
Rowe SP, et al. Initial experience using 99mTc-MIBI SPECT/CT for the differntiaion of oncocytoma from renal cell carcinoma. Clin Nucl Med 2015;40:309-13.
Gorin MA, et al. Prospective Evaluation of 99mTc-sestamibi SPECT/CT for the diagnosis of renal oncocytomas and hybrid oncocytic/chromophobe tumors. Eur Urol 2016;69:413-6.
Tzortzakakis A, et al. Visual evaluation and differentiation of renal oncocytomas from renal cell carcinomas by means of 99mTc-sestamibi SPECT/CT. EJNMMI Res 2017;7:29.
