Fossa navicularis magna detection on cone-beam computed tomography

Abstract

Herein, we report and discuss the detection of fossa navicularis magna, a close radiographic anatomic variant of canalis basilaris medianus of the basiocciput, as an incidental finding in cone-beam computed tomography (CBCT) imaging. The CBCT data of the patients in question were referred for the evaluation of implant sites and to rule out pathology in the maxilla and mandible. CBCT analysis showed osseous, notch-like defects on the inferior aspect of the clivus in all four cases. The appearance of fossa navicularis magna varied among the cases. In some, it was completely within the basiocciput and mimicked a small rounded, corticated, lytic defect, whereas it appeared as a notch in others. Fossa navicularis magna is an anatomical variant that occurs on the inferior aspect of the clivus. The pertinent literature on the anatomical variations occurring in this region was reviewed.

Keywords: Clivus Fossa, Posterior; Cone-Beam Computed Tomography; Multidetector Computed Tomography; Skull Base.

Fig. 1. Sagittal and axial cone-beam computed tomographic images of case 1 demonstrate a notch-like osseous defect in the clivus (arrows) radiographically consistent with fossa navicularis magna.

Fig. 2. Axial and sagittal images of case 2 show a well-defined, osseous defect in the anterior-inferior aspect of the clivus (arrows), demonstrating fossa navicularis magna.

Fig. 3. Coronal, sagittal, and axial images reveal a well-defined, osseous defect within the basiocciput in case 3, as shown by arrows.

Fig. 4. Axial, coronal, and sagittal images in case 4 show a well-defined, round osseous defect noted in the inferior aspect of the clivus, radiographically consistent with fossa navicularis magna.