MKI67 and malignant peripheral nerve sheath tumor: While Martin et al. systematically reviewed the diagnostic accuracy of MRI and PET/CT in differentiating between benign schwannomas and MPNST, several studies have reported that some cases of schwannomas that were diagnosed as malignant owing to increased FDG uptake on PET/CT were finally diagnosed as benign based on the Ki-67 index.19–21) These findings indicate that the preoperative differentiation of benign from malignant schwannomas through PET/CT usually requires validation through pathological examination.