We performed a histological examination and DNA analysis on samples of
tissue from a forty-seven-year-old woman who had a clinical diagnosis of
pigmented villonodular synovitis. The histological examination confirmed
the diagnosis. The evaluation of the samples of tissue with preferential
X-chromosome inactivation analysis (a molecular biological method for the
study of clonality in tumors) showed that the lesion was polyclonal in
origin. We concluded, therefore, that pigmented villonodular synovitis is
more likely to be a reactive process than a true neoplasm.