RESUMEN
From a clinical point of view, all mammary fibroadenomas are similar. However some of them are not visible in mammograms, phenomenom probably related to glandular density. Aiming to elucidate whether the lack of visibility is caused by the glandular density or by tumor itself, a 3 stage study was performed. In 201 cases the mammographic visibility of fibroadenomas was determined and correlated with patients' age, the presence of fibrocystic disease and tumor histological type; after surgical excision, 18 fibroadenomas were sliced into 5 mm thick samples and X rayed to determine their visibility; finally 2 visible and 2 non visible tumors were calcinated at 550ºC and their ashes subjected to X-ray diffraction analysis. Twenty two percent of fibroadenomas were not vosible on mammography, this percentage was higher for intracanicular tumors, in younger women and in the presence of fibrocystic disease. Sixteen percent of excised and sliced tumors were not visible on X rays. Also, differences were found in X-ray diffraction studies between visible and invisible tumors, probably related to NaCl and KCl tumor content