Cytopathology of mesenchymal repair

Tissue repair is a common biologic process closely associated with the inflammatory response. The cytologic features of regeneration and repair of epithelial surfaces have been intensely studied and documented. Regeneration and repair occur in mesenchymal tissues and their radiographic and cytologic findings may closely simulate malignancy. This paper reviews the cytologic features of mesenchymal repair as seen in 44 aspiration biopsy specimens of bone, skeletal muscle, fibroadipose tissue, and fibrous connective tissue. In general, cytologic specimens from such lesions display variable but often scanty cellularity, prominent cellular heterogeneity with a spectrum of atypical features, an admixture of reactive fibroblasts, and evidence of a coexisting inflammatory reaction. Careful attention to cytologic detail and review of clinical and radiographic findings are mandatory in the evaluation of these specimens.