Positron emission tomography of schwannomas: Emphasizing its potential in preoperative planning

Objective. In this article, we describe FDG uptake in schwannoma as measured on positron emission tomography (PET). FDG uptake is compared with tumor cellularity, tumor size, and tumor proliferation rate (M-67 index). Conclusion. Schwannomas generally have a high tumor-to-background ratio on FDG PET. Semiquantitative analysis with standardized uptake values (SUVs) reveals a wide variation in SUVs that can be explained by variations in the degree of cellularity. No correlation was found between FDG uptake and tumor size or tumor proliferation rate (Ki-67 index). Because these tumors often have a high level of FDG uptake, distinguishing schwannomas from malignant peripheral nerve sheath tumors before biopsy or surgery is not possible. Even in cases in which the maximum SUV or average SUV is greater than 6.0, schwannomas cannot be excluded. Therefore, schwannoma should be included in the differential diagnosis of peripheral nerve sheath tumors with low, intermediate, or high SUVs.