Canalis basilaris medianus

Last revised by Francis Deng on 8 Sep 2020

The canalis basilaris medianus (median basal canal), also known as clival canalmedian clival canal, or inferior median clival canal, refers to a number of anatomic variant midline canals in the clivus, typically involving the basioccipital portion.

These canals are generally well-defined, corticated structures, usually less than 2 mm in diameter, that course through the clivus in the sagittal plane (occasionally diagonally).

Six types or variants of the canalis basilaris medianus have been described, divided into two groups 1,6

  • complete (multiple openings in the clivus)
    • canalis basilaris medianus superior: two openings on the dorsal (intracranial) surface
    • canalis basilaris medianus inferior: one opening on the dorsal surface and another on the ventral (nasopharyngeal) surface
    • canalis basilaris medianus bifurcatus: two openings on the dorsal surface and one opening on the ventral surface
  • incomplete (blind-ending canals or deep recesses in the clivus)
    • long channel running through the basiocciput and posterior basisphenoid: one opening on the dorsal surface of the clivus with the blind end terminating posterior/inferior to the sella turcica
    • superior recess in basiocciput: short, blind-ending opening on the dorsal surface
    • inferior recess in basiocciput or large/deep foveola pharyngica (pharyngeal fossa): short, blind-ending opening on the ventral surface

The prevalence of this variant is 1–5% 2-7.

It should not be confused with a horizontal groove or canal, which is sometimes seen thought to represent a venous channel between the inferior petrosal sinuses or a remnant of the first true somite 14.

The canalis basilaris medianus is generally thought to represent a remnant of the notocord. However, some studies of the contents have found no notochordal structures but only venous channels emanating from the basilar plexus 7.

Canalis basilaris medianus was first described by Gruber in 1880 8, but it remains not well known. It is not included in Terminologia Anatomica. In 1987, Zhang and Yen asserted they were the first to describe such canals and termed them inferior median clival canals 5.

This anatomic variant is generally considered of no clinical significance 6, but some pathologies have rarely been reported in association:

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