![]() ![]() 3 4 The incidence of fossa navicularis magna in dry skulls was found to be 5.3%, 5 and using CT, the reported incidence was 3%. In rare instances, fossa navicularis magna may serve as a route for the spread of an infection from the oropharynx to the base of the skull. 9 was approximately 8 mm×6 mm in diameter and was outlined by regular cortical margins in the basiocciput. The fossa navicularis magna reported by Betranello et al. 9 11 12 However, this is in contrast with the study of Cankal et al., 13 who found no soft tissue in the bony dehiscence. It is known that this notch-like osseous bony defect in the basiocciput can be filled with lymphoid tissue of the nasopharyngeal tonsils. 9 colleagues argued that fossa navicularis magna must be differentiated from canalis basilaris medianus, which the authors stated represents the persistence of the chordal canal. On a contradictory note, Beltramello et al. It is possible that fossa navicularis magna may actually be a variant of incomplete canalis basilaris medianus (inferior basiocciput type). 8 It is still unclear if the fossa navicularis magna and canalis basilaris medianus are anomalies from the same notochord remnants however, we theorize that they both are representations of the same notochord remnants with radiographically overlapping features. The initial three types of the canalis basilaris were the inferior, superior, and bifurcated types, and other variants, such as the long-channel, superior, and inferior recess types, were added to the literature more recently. According to the early descriptions, this defect was a well-defined channel, typically more than 2 mm in diameter, originating on the intracranial surface of the basiocciput in the midline very close to the anterior rim of the foramen magnum. 3 7 8 Currarino (1988) 8 referred to a description of the canalis basilaris medianus defect in humans published in the late 19 th century. 4 8 9 10 In the English-language literature, it has been referred to with synonymous names, such as fossa pharyngea, large pharyngeal fossa, and fossa navicularis, with terminological overlap occurring between this developmental anomaly and canalis basilaris medianus. It has been hypothesized that fossa navicularis magna is an anatomical variant that may form from either the persistence or enlargement of emissary veins or as a result of remnants of the notochordal canal. Keywords: Cone-Beam Computed Tomography, Skull Base, Clivus Fossa, Posterior, Multidetector Computed Tomography The pertinent literature on the anatomical variations occurring in this region was reviewed. Fossa navicularis magna is an anatomical variant that occurs on the inferior aspect of the clivus. In some, it was completely within the basiocciput and mimicked a small rounded, corticated, lytic defect, whereas it appeared as a notch in others. The appearance of fossa navicularis magna varied among the cases. CBCT analysis showed osseous, notch-like defects on the inferior aspect of the clivus in all four cases. 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. 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. ![]()
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