Report from ISS: Carbon-11 methionine pumps up PET’s musculoskeletal power

FDG- and carbon-11-labeled methionine PET could narrow down the diagnosis of malignant peripheral nerve sheath tumors in patients with neurofibromatosis, according to a study presented at the 2006 International Skeletal Society meeting in Vancouver.

Differentiating between benign neurofibromas and malignant peripheral nerve sheath tumors has important prognostic and therapeutic implications for patients with neurofibromatosis type 1 (NF1). FDG-PET has shown a remarkable sensitivity in detecting malignant peripheral nerve sheath tumors, but it lacks specificity. Adding C-11 methionine scans to FDG-PET studies could increase their specificity, said principal investigator Dr. Miriam A. Bredella, a radiologist at Massachusetts General Hospital.

Bredella and colleagues performed 47 whole-body FDG-PET scans on 45 patients with NF1 and suspected malignant peripheral nerve sheath tumors based on clinical symptoms and previous imaging studies. Nine patients underwent additional C-11 methionine PET scanning. The researchers evaluated PET images for distribution and uptake patterns, as well as standardized uptake values. They found that adding C-11 methionine PET scans increased the specificity in equivocal cases.

The investigators detected 15 cases of malignant peripheral nerve sheath tumors at surgery, all of which had showed increased uptake on PET. They classified all malignant tumors correctly using FDG or C-11 methionine. Twenty-five patients had benign neurofibromas, which were confirmed at surgery or follow-up. Eight of these patients showed false-positive results on FDG-PET. Five then underwent additional C-11 methionine scanning that showed no evidence of malignancy.

FDG-PET sensitivity and specificity values for detection of malignant peripheral nerve sheath tumors were 100% and 72%, respectively. Adding C-11 methionine PET increased specificity to 95%.