Imaging of soft tissue tumors in the pediatric patient

Abstract

Tumors of the musculoskeletal system are rare in childhood and,when discovered, are worrisome to both parents and physicians. In Kransdorf s series from the Armed Forces Institute of Pathology (AFIP), only 1,330 (5%) of 26,854 soft tissue tumors arose in utero and in young children (05 years) and only 7% in children between 6 and 15 years old [2, 5]. In our series of 982 histologically proven soft tissue tumors, 4% were found in children of 05 years and 9% in those of 615 years [6]. Fortunately, most soft tissue tumors arising in children are benign. In a study performed in Denmark, only 14% of 76 neonates with a congenital malignancy had a soft tissue sarcoma [8]. In the United States, evidence exists that malignancies among children younger than 15 years are increasing in incidence, except for Wilms tumor and soft tissue and bone sarcoma [9]. In a series of the AFIP, 79% of soft tissue tumors in children between 0 to 5 years old are benign, as are 70% in those from 6 to 15 years [2, 5]. In our pediatric series of soft tissue tumors, 90% of the tumors were benign. In contrast, only 60% of soft tissue tumors in adults are benign. The difference in incidences between these two centers could be explained by the referral nature of the AFIP series, with a higher incidence of malignant tumors accumulated during a ten-year period, whereas our series included patients referred to our large community university hospital primarily to undergo diagnostic imaging procedures, especially magnetic resonance (MR) imaging of a soft tissue mass. Some tumors are more frequently encountered in the pediatric age group (Table 27.1) [1032].Most common malignant tumors in children between 0 and 5 years are fibrosarcoma (36% of all malignant soft tissue tumors in this age group), rhabdomyosarcoma (21%), giant cell fibroblastoma (7%), dermatofibrosarcoma protuberans (6%), angiomatoid malignant fibrous histiocytoma (5%) and malignant peripheral nerve sheath tumor (5%). In children between 6 and 15 years, the most common malignant tumors are angiomatoid malignant fibrous histiocytoma (16%), synovial sarcoma (13%), rhabdomyosarcoma (11%), fibrosarcoma (8%), and malignant fibrous histiocytoma (7%). Traditionally, pediatric oncologists have arbitrarily divided soft tissue sarcomas into two groups: rhabdomyosarcoma (RMS), the most common soft tissue sarcoma of childhood,and non-RMS soft tissue sarcomas (NRSTS), a biologically and clinically heterogeneous assortment of tumors.The most common NRSTS in childhood are synovial sarcoma, malignant fibrous histiocytoma, malignant peripheral nerve sheath tumor, and fibrosarcoma. RMS is more common in children less than 10 years of age, whereas the NRSTS predominate in the older age groups [40]. On the contrary, in the files of the Kiel Pediatric Tumor Registry (n=4272 soft tissue malignancies) rhabdomyosarcomas are by far the most frequent sarcomas (44.6% of the cases), followed in decreasing order of frequency by the family of Ewing tumors (peripheral primitive neuroectodermal tumors and extraosseous Ewings sarcomas; altogether 22.3%), malignant peripheral nerve sheath tumors (8.1%), synovial sarcomas (5.0%), leiomyosarcomas (3.2%), fibrosarcomas (2.4%), extrarenal malignant rhabdoid tumors (2%), and alveolar soft tissue sarcomas (1.1%).A further group (11.3%) includes rare tumors, intermediate fibrohistiocytic tumors, and unclassified sarcomas. Embryonal rhabdomyosarcomas are 2.5 times more frequent than the alveolar rhabdomyosarcomas, which are prognostically unfavorable and located predominantly in the extremities and the trunk. With regard to clinical findings, histology, molecular biology and prognosis, embryonal and alveolar rhabdomyosarcomas have to be considered as two different tumor types. The family of Ewing tumors includes extraosseous Ewings sarcoma and peripheral primitive neuroectodermal tumors (synonym: malignant peripheral neuroectodermal tumors), the former tumors without and the latter with neural differentiation. Many cases of infantile malignant peripheral nerve sheath tumors and infantile fibrosarcomas are lowgrade malignancies and are prognostically more favorable than their adult counterparts [26]. The most common benign masses in young children between birth and 5 years are hemangioma (15% of all benign tumors in this age group), fibromatosis (11%), granuloma annulare (10%), infantile myofibromatosis (8%), and lipoblastoma (8%). The most frequent benign tumors in older children (6 to 15 years) are fibrous histiocytoma (17%), nodular fasciitis (16%), hemangioma (13%), and fibromatosis (5%) [2, 5]. The location of soft tissue masses in children varies. In children younger than 6 years of age, almost 60% of benign and malignant lesions occur within the head and neck region, the lower extremity, or the trunk. In children of 6 to 15 years old, benign tumors most often occur in the hand or wrist, the head and neck region, and the lower extremities [2, 5],whereas malignant soft tissue tumors in this age group are more common in the lower or upper extremity or the trunk. Rhabdomyosarcomas in the pediatric age group have a different anatomic distribution when compared with non-rhabdomyosarcoma tumors in children and soft tissue tumors in adults [34]. Many of the primary sites of childhood rhabdomyosarcoma, such as the orbit, bladder, prostate, and paratesticular region are virtually never primary sites of the non-rhabdomyosarcoma tumors in children and of other soft tissue sarcomas in adults [34]. Pediatric soft tissue sarcoma may occur as a second malignant neoplasm due to treatment of a prior primary childhood malignancy and/or genetic susceptibility. In a series of 25 patients treated for different primary tumors second malignant neoplasms occurred after a median of 8 years and included rhabdomyosarcoma, malignant peripheral nerve sheath tumor, extraosseous Ewing family tumor, leiomyosarcoma,fibrosarcoma and synovial cell sarcoma [4].