Pediatric Soft-Tissue Tumors and Pseudotumors: MR Imaging Features with Pathologic Correlation Part 2. Tumors of Fibroblastic/Myofibroblastic, So-called Fibrohistiocytic, Muscular, Lymphomatous, Neurogenic, Hair Matrix, and Uncertain Origin

In the final part of this two-part review article on soft-tissue masses in children, the magnetic resonance (MR) imaging features, clinical findings, and pathologic findings in a wide variety of tumors, including those of fibroblastic/myofibroblastic origin, so-called fibrohistiocytic tumors, smooth-muscle tumors, skeletal-muscle tumors, tumors of uncertain differentiation, and lymphoma, are described. Other neoplasms that are not included in the World Health Organization classification of soft-tissue tumors but may be seen clinically as soft-tissue masses, specifically dermatofibrosarcoma protuberans, neurogenic tumors and pilomatricoma, are also included. In contrast to the tumors reviewed in Part 1 of this review, the MR imaging features and clinical findings of the tumors included here are largely nonspecific. However, MR imaging is useful in determining site of tumor origin, extent of disease, and relation of tumor to adjacent anatomic structures, and for follow-up after therapy. In some of these entities, the combination of findings may aid in narrowing the differential diagnosis, such as persistent low signal intensity on T1- and T2-weighted images in some fibroblastic lesions, identification of hemosiderin and a synovial origin in pigmented villonodular synovitis, or the presence of multiple target signs on T2-weighted images in deep plexiform neurofibroma. In a large number of cases, however, tissue biopsy is required for final diagnosis.