Quantitative F18-fluorodeoxyglucose positron emission tomography accurately characterizes peripheral nerve sheath tumors as malignant or benign

Abstract

Background: Correct pretreatment classification is critical for optimizing diagnosis and treatment of patients with peripheral nerve sheath tumors (PNSTs). The aim of this study was to evaluate whether F18-fluorodeoxyglucose positron emission tomography (FDG PET) can differentiate malignant (MPNST) from benign PNSTs.

Methods: Thirty-four adult patients presenting with PNST who underwent a presurgical FDG PET/computed tomography (CT) scan between February 2005 and November 2008 were included in the study. Tumors were characterized histologically, by FDG maximum standardized uptake value (SUV(max) [g/mL]), and by CT size (tumor maximal diameter [cm]). The accuracy of FDG PET for differentiating MPNSTs from benign PNSTs (neurofibroma and schwannoma) was evaluated by receiver operating characteristic (ROC) curve analysis.

Results: SUV(max) was measured in 34 patients with 40 tumors (MPNSTs: n = 17; neurofibromas: n = 9; schwannomas: n = 14). SUV(max) was significantly higher in MPNST compared with benign PNST (12.0 +/- 7.1 vs 3.4 +/- 1.8; P < .001). An SUV(max) cutoff point of > or =6.1 separated MPNSTs from BPSNTs with a sensitivity of 94% and a specificity of 91% (P < .001). By ROC curve analysis, SUV(max) reliably differentiated between benign and malignant PNSTs (area under the ROC curve of 0.97). Interestingly, the difference between MPNSTs and schwannomas was less prominent than that between MPNSTs and neurofibromas.

Conclusions: Quantitative FDG PET imaging distinguished between MPNSTs and neurofibromas with high accuracy. In contrast, MPNSTs and schwannomas were less reliably distinguished. Given the difficulties in clinically evaluating PNST and in distinguishing benign PNST from MPNST, FDG PET imaging should be used for diagnostic intervention planning and for optimizing treatment strategies.

Conflict of interest statement

CONFLICT OF INTEREST DISCLOSURES

Figures

Figure 1

(A) The maximum standard uptake value (SUVmax) of each lesion is represented by 1 symbol. Mean and standard deviation are depicted for each group. The mean SUVmax of malignant peripheral nerve sheath tumors (MPNSTs) was significantly higher than that of benign PNSTs (P < .001). A cutoff value of 6.1 identified 16 of 17 malignant PNSTs as true positive and 21 of 23 benign lesions as true negative (sensitivity, 94%; specificity, 91%; accuracy, 93%). (B) The corresponding maximum tumor diameters of each lesion are depicted. MPNSTs were significantly larger than the benign variants (P = .008). However, there was considerable overlap in tumor size between malignant and benign tumors. NF1 indicates neurofibromatosis type 1.

Figure 2

Receiver operating characteristic (ROC) curves for assessment of malignancy by tumor metabolic activity (solid line) and tumor size (dotted line) are shown. The gray line indicates the expected ROC curve for random guessing of malignancy. SUVmax indicates maximum standard uptake value; AUC, area under the curve.

Figure 3

(A) A positron emission tomography/computed tomography study in a patient with neurofibromatosis (NF) type 1-associated malignant peripheral nerve sheath tumor (MPNST) is depicted. The MPNST is located in the right distal thigh (maximum standard uptake value [SUVmax], 14.9) and arises from a benign neurofibroma. A neurofibroma with lower F18-fluorodeoxyglucose uptake (SUVmax, 2.3) is located in the left medial thigh. (B–D) The histologic findings of the patient’s right thigh lesion are depicted. (B) A region of benign neurofibroma (original magnification, ×20) shows the usual low cellularity and slender spindled cells with interspersed pink collagen fibers. Note that no mitoses or necrosis is present. (C) A low-power view (original magnification, ×2) shows transition from neurofibroma (lower left corner) to high-grade MPNST (upper right corner). Note the increase in cellularity from the benign to the malignant area. (D) A high-power view (original magnification, ×20) of the high-grade MPNST is shown. Note the marked increase in cellularity, obvious mitoses, and nuclear pleomorphism. Extensive necrosis (not pictured here) was also present.

Figure 4

(A) A schwannoma with high F18-fluorodeoxyglucose (FDG) uptake located in the pelvis is depicted. (B) By comparison, a patient with a schwannoma located in the right retroperitoneum with low FDG uptake is shown. This illustrates the wide range of maximum standardized uptake value (SUVmax) among schwannomas. Despite an extensive histopathologic and immunohistochemical analysis, we could not detect differences that could account for the divergent FDG uptake of these 2 schwannomas.