Somatostatin Receptor (SSTR) PET scans (e.g. Ga68/Cu64) have transformed the imaging landscape for Neuroendocrine Cancer, mainly for well-differentiated NETs, most of which will be somatostatin receptor positive.  However, Oncologists/NET Specialists and radiologists must be aware of the various physiologic and other pathologic processes in which cellular expression of SSTR can result in interpretative error.  Included in these pitfalls are incidental findings. 

What is an incidental finding? 

An incidental finding, also known as an incidentaloma, may be defined as “an incidentally discovered mass or lesion, detected by CT, MRI, or other imaging modality (e.g. PET) performed for an unrelated reason.”  An increase in the utilisation of imaging examinations over the past three decades has led to a marked increase in the number of findings detected that are unrelated to the primary objectives of the examinations.

This study cited below covers the prevalence and significance of incidental findings related to Ga68 PET scans (it is likely to be similar to other SSTR PETs).  In fact, this study is a collation of many other studies covering a total of 2906 subjects.  The output is interesting and reinforces the need for careful interpretation of scans.

The study concluded that:

“The most incidental SSTR PET/CT findings were found in the thyroid gland, spine, and brain. The risk of malignancy was greatest in incidental SSTR PET/CT findings in the breast, cranially, and thyroid gland. The results of the present study can prove useful in the interpretation of atypical findings on SSTR PET/CT and in the counseling of clinicians.”

Using abstract data from the report, the incidental breast findings were associated with the highest risk of malignancy (67%). In the thyroid, incidental SSTR uptake was caused by malignancy in 8%, all presenting as focal uptake. The lowest risk was seen in the spine with a malignancy rate of 3% in patients with incidental SSTR uptake and benign cases were interpreted as vertebral hemangiomas on CT. Incidental SSTR PET/CT findings in other locations were of malignant etiology in two out of six cases (33%) and should be evaluated individually.  The study has details of the other locations. 

These findings in terms of locations correlate nicely with the seminal paper from Dr Michael Hofman which was covered in the pitfalls section of my general SSTR PET post linked below.  The other interesting study output is the malignancies discovered in the incidental finding indicate most incidental findings are benign in nature.  However, it also emphasises the importance of thorough checking when things are found incidentally via scans.  In fact, many people will have been diagnosed with NET via the same process!  

But something I emphasise in my ‘Understanding your SSTR PET Reports‘ blog post linked below, not everything that lights up on SSTR PET is NET and not everything that lights up on SSTR PET is a malignancy.