The difficulty in visualizing the true nature of apical periodontitis because of the superimposition of unrelated structures onto the features of interest is reduced when tomographic slices are used instead of images in which an entire volume of data is compressed into a planar image. This periapical radiographic image (upper left) of the maxillary left second molar shows no radiographic signs of pathosis. A contemporaneously exposed CBCT image, upper right, corrected sagittal reformation), shows a 4.3 x 1.9 mm well-defined unilocular, noncorticated area of low attenuation centered over the apex of the mesiobuccal root, consistent with a perpendicular periodontitis, yellow arrow.  there is a moderate mucositis in the region of the maxillary sinus adjacent to this tooth, blue arrow. Experimental semi-automated segmentation of this image using active contour methods (ITK-SNAP) allowed for measurement of the true volume of the lesion, lower right.