Fossa navicularis magna
Fossa navicularis magna, or sometimes simply fossa navicularis, is a variant depression on the ventral/inferior surface of the basioccipital portion of the clivus. It is a notch-like or rounded defect upon which the smaller pharyngeal fossa (foveola pharyngica) is superimposed . The prevalence is 1–8% .
Fossa navicularis magna is often confused with canalis basilaris medianus, of which one incomplete type may be called an enlarged pharyngeal fossa. They may both represent the same spectrum of osseous defects presumably related to notochord migration .
If making a distinction is desired based on their names, it may be more suitable to use "fossa" navicularis magna when the defect is a depression where the opening is wider than it is deep, and "canalis" basilaris medianus when the defect is a tubular structure where the opening is narrower than it is deep.
Fossa navicularis magna is generally considered of no clinical significance, but there are rare reports of it acting as a route for infection to spread from the nasopharynx to the skull base and intracranial compartment .