REVIEW Soft tissue tumours: imaging strategy Hervé J. Brisse & Daniel Orbach & Jerzy Klijanienko Received: 11 January 2010 / Accepted: 30 January 2010 # Springer-Verlag 2010 Abstract Vascular tumours and malformations, fibrous and fibrohistiocytic tumours and pseudotumours are the most common benign soft-tissue masses observed in children, and can be treated conservatively. Rhabdomyosarcomas are the most frequent malignant tumours, accounting for about half of soft tissue sarcomas. A child referred for a soft- tissue mass should ideally be managed by a multidisciplin- ary team and primary excision should be proscribed until a definite diagnosis has been established. Clinical examina- tion, conventional radiography and US with Doppler represent the first-line examinations and are sometimes sufficient to make a diagnosis. In all other situations, MRI is mandatory to establish the aggressiveness and extension of the tumour. This technique provides the relevant data to guide the decision regarding tissue sampling. Keywords Soft tissue . Tumour . US . MRI . Child . Neoplasms . Children Introduction The most frequent benign soft-tissue masses occurring during childhood are benign and can be treated by non- mutilating surgery or even conservatively. This group chiefly includes vascular tumours or malformations, fibrous and fibrohistiocytic tumours and pseudotumours [1, 2]. Malignant tumours predominantly consist of rhabdomyo- sarcomas (RMS), representing about 50% of all soft tissue sarcomas and 4% of solid malignancies in children [3–5]. The most frequent non-RMS malignant tumours are peripheral primitive neuroectodermal/Ewing sarcoma fam- ily tumours (pPNET/Ew) accounting for about 19% of all soft tissue sarcomas, malignant peripheral nerve sheath tumours (MPNST) for 6.5%, infantile fibrosarcomas for 6% and synovial sarcomas (SNVS) for 5% [3]. Characterization of a soft-tissue tumour is based on pathology, immunohistochemistry and molecular biology studies. Histopathology represents the most important step in reaching a correct diagnosis. Microscopic features on conventionally stained sections are first analyzed to classify the lesion. Immunohistochemistry is then used with panels of antigens. However, 5–15% of lesions remain unclassified in the reference histopathological classifications [2, 6]. Cytogenetics and molecular biology now make a consider- able contribution to the diagnosis [7]. These techniques can identify tumours by their genetic alterations (mainly trans- locations) detected by cytogenetic techniques, fluorescence in situ hybridization (FISH) or by molecular biology with RT-PCR (reverse-transcriptase polymerase chain reaction), which identifies the corresponding fusion transcripts (chi- H. J. Brisse (*) Department of Radiology, Institute Curie, 26 rue d’Ulm, Paris 75005, France e-mail: herve.brisse@curie.net D. Orbach Department of Paediatric Oncology, Institute Curie, Paris, France J. Klijanienko Department of Pathology, Institute Curie, Paris, France Pediatr Radiol (2010) 40:1019–1028 DOI 10.1007/s00247-010-1592-z