Multimodal Imaging in Neurofibromatosis Type 1-associated Nerve Sheath Tumors

Abstract

Neurofibromatosis type 1 (NF1) is a neurogenetic disorder. Individuals with NF1 may develop a variety of benign and malignant tumors of which peripheral nerve sheath tumors represent the most frequent entity. Plexiform neurofibromas may demonstrate a locally destructive growth pattern, may cause severe symptoms and may undergo malignant transformation into malignant peripheral nerve sheath tumors (MPNSTs). Whole-body magnetic resonance imaging (MRI) represents the reference standard for detection of soft tissue tumors in NF1. It allows for identification of individuals with plexiform neurofibromas, for assessment of local tumor extent, and for evaluation of whole-body tumor burden on T2-weighted imaging. Multiparametric MRI may provide a comprehensive characterization of different tissue properties of peripheral nerve sheath tumors, and may identify parameters associated with malignant transformation. Due to the absence of any radiation exposure, whole-body MRI may be used for serial follow-up of individuals with plexiform neurofibromas. ¹⁸F-fluorodeoxyglucose positron-emission-tomography (FDG PET/CT) allows a highly sensitive and specific detection of MPNST, and should be used in case of potential malignant transformation of a peripheral nerve sheath tumor. PET/CT provides a sensitive whole-body tumor staging. The use of contrast-enhanced CT for diagnosis of peripheral nerve sheath tumors is limited to special indications. To obtain the most precise readings, optimized examination protocols and dedicated radiologists and nuclear medicine physicians familiar with the complex and variable morphologies of peripheral nerve sheath tumors are required.

Key points:

• Individuals with NF1 may develop benign and malignant nerve sheath tumors.

• Whole-body MRI is the reference standard to identify nerve sheath tumors in NF1.

• MRI provides a comprehensive characterization of the growth pattern, growth dynamics and extent of nerve sheath tumors.

• ¹⁸F-FDG PET/CT provides a sensitivity of 100 % and a specificity of 77 – 95 % for detection of malignant transformation.

Citation Format:

• Salamon J, Mautner VF, Adam G et al. Multimodal Imaging in Neurofibromatosis Type 1-associated Nerve Sheath Tumors. Fortschr Röntgenstr 2015; 187: 1084 – 1092

Zusammenfassung

Die Neurofibromatose Typ 1 (NF1) ist eine neurogenetische Erkrankung, die mit der Entwicklung unterschiedlicher benigner und maligner Tumoren einhergeht, wobei periphere Nervenscheidentumoren die häufigste Entität darstellen. Plexiforme Neurofibrome können lokal destruktiv wachsen, eine ausgeprägte Symptomatik verursachen und unterliegen dem Risiko einer malignen Transformation in maligne periphere Nervenscheidentumoren (MPNST). Die Ganzkörper-Magnetresonanztomografie (MRT) stellt den Referenzstandard zur Detektion von Weichteiltumoren bei NF1 dar und erlaubt die Identifikation von Individuen mit plexiformen Neurofibromen, eine Erfassung der lokalen Tumorausbreitung und die Bestimmung der Ganzkörpertumorlast in T2-gewichteten Sequenzen. In der multiparametrischen MRT kann eine umfassende Charakterisierung der Gewebeeigenschaften von peripheren Nervenscheidentumoren erfolgen; zudem können auf MPNST hinweisende Parameter sensitiv erfasst werden. Aufgrund der fehlenden Strahlenexposition eignet sich die Ganzkörper-MRT für serielle Verlaufskontrollen bei Patienten mit plexiformen Neurofibromen. Die ¹⁸F-Fluordesoxyglukose-Positronen-Emissions-Tomografie (FDG PET/CT) erlaubt eine hochsensitive und spezifische Detektion von MPNST und sollte beim Verdacht auf eine maligne Transformation eines Nervenscheidentumors eingesetzt werden. Dadurch erfolgt gleichzeitig ein sensitives Ganzkörperstaging. Die alleinige kontrastmittelgestützte CT ist heutzutage in der Diagnostik peripherer Nervenscheidentumoren nur noch in Sondersituationen indiziert. Für eine optimale Diagnostik bei Individuen mit NF1 sollten spezifische Untersuchungsprotokolle eingesetzt werden, und Radiologen und Nuklearmediziner sollten mit der komplexen und variablen Morphologie peripherer Nervenscheidentumoren vertraut sein.

Key words

NF1 - neurofibromatosis - MPNST - MRI - PET

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