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Background
Pediatric fibro-osseous lesions (FOLs) encompass a variety of skeletal and soft tissue diseases that are developmental, dysplastic, reactive or neoplastic in origin. These lesions have common microscopic features, consisting of bland appearing fibroblastic proliferation with intermixed woven bone deposition. Musculoskeletal FOLs constitute a heterogeneous group including skeletal lesions such as fibrous dysplasia (FD), juvenile ossifying fibroma (JOF), metabolic disease such as Brown’s tumor in hyperparathyroidism, and non-ossifying fibroma (NOF). Lesions can be solitary, or polyostotic as in syndromes such as Mazabraud and McCune-Albright. Soft tissue lesions include phosphaturic mesenchymal tumors (PMTs), fibromatosis and fibrous hamartoma of infancy.

Educational Goals / Teaching Points
Through this exhibit we describe the various skeletal and soft tissue FOLs encountered in the pediatric population. We will briefly discuss the pathogenesis of these lesions and describe the imaging features on various conventional and advanced modalities while describing cases. We will attempt to describe the radio-pathological correlations for cases wherever possible.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
In view of the different management strategies and syndromic associations, accurate diagnosis as well as characterization of these lesions is necessary. Imaging is a noninvasive tool that can preclude further workup in certain “no-touch” lesions with typical features such as FD and NOF. The exact extent and activity of lesions can be described with use of newer modalities such as multiplanar and functional imaging. Suspected tumor-causing oncogenic osteomalacia can be localized using uptake on DOTANOC (Positron Emission Tomography) PET and Gallium 68 DOTATATE studies, in case of rare PMTs. Skeletal surveys utilize conventional radiography in recognizing the polyostotic nature of the diseases such as syndromic FD and skeletal manifestations in PMTs. Computed Tomography (CT) provides the benefit of multiplanar reconstruction and defines the anatomy of the involved region. Magnetic resonance imaging (MRI) enables superior characterization of the lesion without any radiation exposure which is beneficial in context of the growing skeleton. Follow-up imaging is necessary in the posttreatment phase to recognize treatment benefit and locate recurrence.

Conclusion
Pediatric FOLs have wide morphological presentations. Imaging has a role in identifying these pathologies as well as delineating accurate extent. Advanced nuclear medicine imaging can detect specific activity in a subset of these lesions.