Measuring pituitary tumor volume: a comparison of the simplified and non-simplified ellipsoid equation with the 3D planimetric volume assessment.

Purpose: The ellipsoid equation came in an attempt to facilitate the estimation of tumor volume, by measuring the height, width, and anteroposterior length of the lesion. The estimated tumor volume can sometimes be different between methods, thus, it is of extreme interest to evaluate if the methods are significantly different, as well as to discuss the main limitations of each one.

Methods: This is an observational, analytical, cross-sectional study. A systematic review of the literature was also performed in order to discuss the results observed in the present study.

Results: A total of 82 patients (43 males and 39 females) ranging in age from 15 to 78 years (mean 47.95 ± 14.76) were included in the study. Seven patients were classified as Knosp grade 0 (8.5%), 36 Knosp grade 1 (44%), 14 Knosp grade 2 (17%), 20 Knosp grade 3 (24.4%), 5 Knosp grade 4 (6.1%). The tumor volume estimated by 3D planimetric assessment, non-simplified ellipsoid equation, and simplified ellipsoid formula averaged 10.68 cm³, 10.36 cm³, and 9.9 cm³ respectively.

Conclusion: A simplified form of the ellipsoid equation increases the divergence between the measurement obtained in planimetry, and should be discouraged, in view of the new automated methods of performing quick calculations using periodic digits. The non-simplified form underestimated the tumor volume by 2.9% on average but did so regularly. In clinical practice, measurement should be accompanied by an evaluation of tumor morphology.