Potential role of 18fluorodeoxyglucose-positron emission tomography/computed tomography in differentiating benign neurofibroma from malignant peripheral nerve sheath tumor associated with neurofibromatosis 1.

OBJECTIVE

Benign plexiform neurofibromas (PNfib), especially those occurring in patients with neurofibromatosis type 1, are at a significant risk of progressing to a malignant peripheral nerve sheath tumor (MPNST). Early diagnosis, followed by radical surgery and adjuvant radiation to maintain local tumor control, is of critical importance to prevent metastasis and subsequent mortality from MPNSTs. However, early diagnosis is hampered by the sensitivity of current imaging modalities such as computed tomography (CT) or magnetic resonance imaging to reliably detect this malignant transformation, which can occur heterogeneously in a PNfib to a MPNST. 18Fluorodeoxyglucose (18FDG)-positron emission tomography (PET) is linked to metabolism and proliferation of tissues and has been widely used in oncology including PNSTs. 18FDG-PET/CT has the added advantage of fusing metabolic and anatomic imaging data sets.

METHODS

In this prospective study, 9 neurofibromatosis type 1-associated PNfibs suspected to have undergone transformation to an MPNST were preoperatively evaluated by 18FDG-PET/CT and magnetic resonance imaging. A detailed histological evaluation correlated the average and regional standard uptake value (SUV) from the 18FDG-PET/CT to grade of malignancy of the suspected MPNST.

RESULTS

Imaging from 18FDG-PET/CT and associated SUV of the suspected MPNSTs demonstrated either a homogeneous or a heterogeneous pattern. Stratification of the maximal SUV to low (<4.0), intermediate (4.0-7.0), or high (>7.0) correlated to the proliferative index (Ki-67) and grade of MPNST. A maximal SUV of more than 7.0 was closely correlated to a focus of malignant transformation.

CONCLUSION

This study, on a limited number of cases, demonstrates the potential use of 18FDG-PET/CT to augment management of PNfibs, especially in the context of neurofibromatosis type 1, which is characterized by multiple tumors. The addition of CT anatomic imaging to 18FGD-PET can facilitate targeting biopsies to metabolic hot spots, to further augment diagnostic sensitivity. Much larger numbers of MPNSTs, which can only be accrued in a collaborative manner among institutions, are required to further assess the specificity and sensitivity of 18FDG-PET/CT in the diagnosis of MPNSTs.