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Foreign Body Abscess Mimicking a Malignant Peripheral Nerve Sheath Tumor in a Patient With Neurofibromatosis Type 1 Johannes Salamon, MD,* Christian Hagel, MD,† Reinhard E. Friedrich, MD,‡ Victor F. Mautner, MD,§ and Thorsten Derlin, MD* Abstract: We report a case of a 47-year-old man with neurofibromatosis type 1 presenting with a growing and painful lesion within the right thigh, suggesting a malignant peripheral nerve sheath tumor. MRI showed a T2-weighted hyperintense lesion with surrounding edema and contrast enhancement. 18F-FDG PET/CT demonstrated inhomogeneously increased tracer uptake within the right thigh. Histopathologic evaluation revealed a foreign body with purulent fibroinflammatory reaction. 18F-FDG PET/CT is a highly sensitive tool for detection of malignant transformation in neurofibromatosis type 1, but false-positive findings may be observed in benign lesions, for example, inflammatory processes. Key Words: neurofibromatosis type 1, malignant peripheral nerve sheath tumor, MPNST, foreign body, PET/CT, MRI (Clin Nucl Med 2015;40: 674–675)

Received for publication October 28, 2014; revision accepted March 10, 2015. From the *Department of Diagnostic Interventional Radiology, †Institute of Neuropathology, Departments of ‡Oral Maxillofacial Surgery, and §Neurology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany. Conflicts of interest and sources of funding: none declared. Reprints: Johannes Salamon, MD, Department of Diagnostic and Interventional Radiology, University Medical Center Hamburg-Eppendorf, Martinistraße 52 D-20246 Hamburg, Germany. E-mail: [email protected] Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved. ISSN: 0363-9762/15/4008–0674 DOI: 10.1097/RLU.0000000000000824

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Clinical Nuclear Medicine • Volume 40, Number 8, August 2015 Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.

Clinical Nuclear Medicine • Volume 40, Number 8, August 2015

Foreign Body Abscess Mimicking MPNST in a Patient

FIGURE 1. A 47-year-old man with neurofibromatosis type 1 (NF1) presented with a rapidly growing, painful lesion of the right thigh. No leukocytosis was observed; the serum concentration of C-reactive protein level was slightly elevated (12 mg/L). A prior injury was not remembered. The patient underwent whole-body 18F-FDG PET/CT and whole-body MRI for further evaluation. MIP PET image (A) showing inhomogeneous tracer uptake subcutaneously and subfascial between the biceps femoris and semitendinosus muscle of the right thigh. Axial PET (B) and fused PET/CT (C) images demonstrating inhomogeneously increased 18F-FDG uptake (SUVmax, 8.0). Corresponding contrast-enhanced T1-weighted MRI with fat suppression (D) showing inhomogeneous, in part rim-like contrast enhancement. Coronal (E) and transversal (F) T2-weighted MR images with fat suppression demonstrating a hyperintense soft tissue lesion with surrounding edema. Imaging suggested a malignant peripheral nerve sheath tumor (MPNST) because of SUVmax greater than 3.5, peripheral contrast enhancement, perilesional edema-like zones, and heterogeneity of tracer uptake. No other metabolically active lesions were detected. The patient underwent surgical resection. Histopathological evaluation (hematoxylin-eosin stain, G) revealed a vascularized foreign body granuloma with chronic purulent inflammatory infiltrates and clefts lined by macrophages and fibroblasts. During surgery, a sliver of wood was found within a subcutaneous abscess with subfascial spread between the biceps femoris and the semitendinosus muscle. Even on specific enquiry, an injury could not be recalled. NF1 is an autosomal dominant neurogenetic disease with an incidence of 1:3.000 individuals.1 Because of a mutation in the tumor suppressor gene neurofibromin, NF1 patients have an increased risk of developing a variety of tumors including benign and MPNSTs,2,3 which arise from Schwann cells.4,5 A subtype of PNSTs, plexiform neurofibromas, occurs in about 30% of NF1 patients. These tumors may cause pain and undergo focal transformation into MPNSTs.6 NF1 patients have a lifetime risk of up to 10% to develop an MPNST, which is at least 100-fold higher than for the general population.7 An increase in size or newly occurred pain in a preexisting tumor might indicate malignant change.8 Whole-body imaging including MRI and PET/CT enables early detection of aggressive and rapidly metastasizing MPNSTs, allowing for potentially curative resection. MRI may be used to determine overall tumor burden but has low specificity for detection of MPNSTs.7–9 MRI-derived parameters suggestive of malignancy include irregular contrast enhancement, perilesional edema, cystic lesions, and intratumoral lobulation.9 18F-FDG PET/CT is both sensitive and specific for identification of MPNSTs.10 An SUVmax cutoff of greater than 3.5 and intratumoral heterogeneity of tracer uptake are used to identify MPNST, and sensitivity of PET/CT may reach 100%.11 To increase the specificity, the use of a tumor-to-liver ratio greater than 2.6 has recently been suggested.12 18 F-FDG PET/CT is a highly sensitive tool for detecting malignant transformation in NF1-associated tumors,8–12 but false-positive findings may be observed in benign lesions as demonstrated in this report. Histopathological evaluation is therefore required in all lesions suggestive of an MPNST. This report highlights an unusual potential reason for false-positive findings in NF1 on 18F-FDG PET/CT.

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Foreign Body Abscess Mimicking a Malignant Peripheral Nerve Sheath Tumor in a Patient With Neurofibromatosis Type 1.

We report a case of a 47-year-old man with neurofibromatosis type 1 presenting with a growing and painful lesion within the right thigh, suggesting a ...
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