Jpn J Radiol (2009) 27:320–323 DOI 10.1007/s11604-009-0343-2
Plurifocal malignant peripheral nerve sheath tumor demonstrated by 18F-fluorodeoxyglucose positron emission tomography/computed tomography Francesco Bertagna · Giovanni Bosio · Giorgio Biasiotto Giordano Savelli · Carlo Rodella · Raffaele Giubbini Josh Rosenbaum · Abass Alavi
Received: May 18, 2009 / Accepted: June 14, 2009 © Japan Radiological Society 2009
Abstract Malignant peripheral nerve sheath tumors (MPNSTs) are sarcomas that derive from peripheral nerves or from cells associated with the nerve sheath. Magnetic resonance imaging is the main diagnostic imaging modality for evaluating MPNSTs. Computed tomography (CT) of the chest is the main imaging modality used to screen for distant disease, and bone scanning is considered useful for identifying selected metastases. Fluorodeoxyglucose positron emission tomography (FDG-PET) has been useful for differentiating malignant nerve sheath tumors from benign lesions and appears to be able to forecast prognosis. We report a case of a patient with neurofibromatosis 1 (NF1) with a histological diagnosis of MPNST, which was diagnosed by biopsy of a posterior right thigh mass examined by 18F-FDG-PET/CT.
Key words PET · Malignant peripheral nerve sheath tumor (MPNSTs) · Neurofibromatosis
F. Bertagna (*) · G. Bosio · G. Savelli Department of Nuclear Medicine, Spedali Civili di Brescia, Piazza Spedali Civili, 1, 25123 Brescia, Italy Tel. +39-30-3995468; Fax +39-30-3995420 e-mail: [email protected]
Malignant peripheral nerve sheath tumors (MPNSTs) are sarcomas that derive from peripheral nerves or from cells associated with the nerve sheath (Schwann cells, perineural cells, fibroblasts). They may develop in patients affected by neurofibromatosis 1 (NF1). Neurofibromas are the most common tumor associated with NF1, and the plexiform neurofibroma subtype represents a major cause of morbidity.1 MPNSTs usually arise from preexisting benign plexiform neurofibromas and metastasize widely. Differentiating between benign and malignant tumours is extremely important as MPNSTs frequently have a poor prognosis but can be difficult to find in the presence of multiple benign tumors. The clinical manifestations of malignancy include pain not otherwise explained, rapid increase in the size of the lesion, change in consistency, and neurological deficit.2,3
G. Biasiotto Dipartimento Materno Infantile e Tecnologie Biomediche, University of Brescia, Brescia, Italy
C. Rodella Health Physics Unit, Spedali Civili Brescia, Brescia, Italy R. Giubbini Department of Nuclear Medicine, University of Brescia, Brescia, Italy J. Rosenbaum · A. Alavi Division of Nuclear Medicine, University of Pennsylvania Medical Center, Philadelphia, PA, USA
We report the case of a patient with NF1 with a histological diagnosis of MPNST diagnosed by biopsy of a posterior right thigh mass. The patient underwent fluorodeoxyglucose-positron emission tomography/ computed tomography (18F-FDG-PET/CT) for staging purposes following magnetic resonance imaging (MRI), CT, and ultrasonography (US). 18F-FDG-PET/CT was performed in the fasting state (at least 6 h); the glucose
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Fig. 1. Coronal positron emission tomography (PET) images show high uptake at the posterior right thigh mass
Fig. 2. Coronal PET images showing high uptake at the popliteal mass
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Fig. 3. Axial computed tomography (CT), PET, and fusion images of the pectoral lesion
level was 82 mg/dl. A FDG dose of 424 MBq was administered intravenously and a two-dimensional (2D) mode ordered subset–expectation maximization (OS-EM) imaging (with septa) was acquired 60 min after injection on a Discovery ST PET/CT tomograph (General Electric, Milwaukee, WI, USA) with standard CT parameters (80 mA, 120 KV without contrast; 4 min per bed–PET–step of 15 cm). The reconstruction was performed in a 128 × 128 matrix and 60 cm field of view. The PET images were analyzed visually and semiquantitatively by measuring the standardized uptake value (SUV). The study revealed intense maximum uptake at the mass located in the right thigh (SUVmax 4.8) (Fig. 1), left popliteal region (SUVmax 3.7) (Fig. 2), and right major pectoral muscle (Fig. 3). Light uptake (SUVmax 1.5–3.0) was present at some of the solid masses described
on CT at the left supraclavicular region and paratracheal and paraesophageal regions near the ninth thoracic vertebra. No uptake was seen at other solid masses in the right iliac fossa or right gluteus probably because of their benign nature.
Discussion MPNSTs are aggressive tumors, and the patients’ prognosis is generally poor. Accurate staging to identify widespread disease and discriminate benign lesions from malignant ones, which significantly affects the prognosis, is essential. Magnetic resonance imaging is the main diagnostic imaging modality as it allows precise evaluation of the planes invaded, the tumor’s heterogeneity, its margins,
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and the presence of edema surrounding the lesion. MPNSTs are commonly found in the extremities (46%– 61%) and the trunk (15%–46%). The large and medium nerves are more frequently affected by these lesions.4,5 MPNSTs usually metastasize to the lungs, bone, and pleura with a local recurrence rate of 40%-65% and a distant recurrence rate of 40%-68%. Computed tomography of the chest is the main imaging tool to screen for distant disease, and bone scanning is useful for identifying metastatic bone disease. 18 F-FDG-PET/CT imaging has been widely used in oncology, but its value for assessing MPNSTs—even though it has been demonstrated to be useful in published papers—is not extensively studied in the literature.6–8 18F-FDG-PET/CT is extremely helpful for differentiating malignant nerve sheath tumors from benign lesions and therefore may provide prognostic information in this setting.2,9 In particular, Ferner et al. studied 105 patients with NF1 tumors, including 29 cases of MPNST, showing high diagnostic accuracy (sensitivity 89%, specificity 95%).9 Even in our single case, the results confirmed the high accuracy of 18FFDG-PET/CT and its diagnostic value in a patient with multiple lesions. Most plexiform neurofibroma subtype (PN) lesions are benign and have low FDG–PET SUV values. FDGPET/CT imaging predicts PN tumor growth in patients with NF1; it may help in decision making1 and is a highly sensitive and specific imaging modality for the diagnosis of MPNST in NF1 patients. Some authors recommend performing early (90 min) and delayed (4 h) imaging for accurate lesion characterization, using a cutoff SUVmax of 3.5 to achieve the best compromise between sensitivity and specificity in the diagnosis of MPNSTs.3 In our study, we had a reliable metabolic lesion evaluation 60 min after the injection with a less time-consuming procedure and better patient throughput. The treatment of choice is surgical resection, when feasible, to achieve complete excision of the tumor. Radiation therapy (before and after surgery) is also an important therapeutic modality in the management of these patients. Chemotherapy is usually used for systemic and metastatic disease and is employed only for high-grade disease.10
Conclusion In this clinical case, 18F-FDG-PET/CT helped with the discrimination between benign lesions related to the known NF1 from the malignant transformed ones. It also assisted clinician decision making.
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