Aneurysmal bone cyst and telangiectatic osteosarcoma. A histopathological and morphometric study.

In a series of 105 cases of aneurysmal bone cyst, 18 showed an unusually high level of mitotic activity and/or increased nuclear pleomorphism which complicated the differential diagnosis with respect to telangiectatic osteosarcoma. An attempt was made to use semi-automatized morphometric and histophotometric techniques to establish objective morphological differences between these unusual cases of aneurysmal bone cyst and 16 cases of telangiectatic osteosarcoma. Three cases (two of aneurysmal bone cyst and one of telangiectatic osteosarcoma) proved unsuitable for analysis. In 24 of the remaining 31 cases (77%) a computerized discriminant analysis permitted correct discreimination with a high degree of certainty on the basis of quantitative nuclear characteristics determined in paraffin sections. In the other 7 cases the diagnosis was less certain (3), doubtful (2) or erroneous (2). The relevant nuclear characteristics were (in ascending sequence of discrimination): the largest nuclear surface area, the mitotic index, and the percentage of nuclear sections exceeding an arbitrarily chosen limit of 60 micron2. The criterion of nuclear size for discrimination between these benign and malignant lesions could be applied for two reasons: firstly, because a group of extremely large nuclei occur in malignant cases, and secondly, because the average nuclear size is larger in malignant than in benign lesions. The extremely large nuclei occur as only a small percentage of the total nuclear population. The other variables investigated, i.e., cellularity and nuclear contour ratio, did not contribute greatly to the differentiation. In 11 cases, the average nuclear Feulgen extinction was estimated as an additional variable.