The foramen rotundum is a small canal deeply situated in the base of the skull which represents the way of exit of the maxillary nerve, second branch of the trigeminal nerve. Its precise individualization and analyse is difficult and necessitates a precise and adapted technique as well as a precise knowledge of its anatomical relationships. Its represents a frontier area between the endo- and exocranial spaces. Its involvement which is preferentially related with tumoral pathologies (and particularly with retrograde perineural invasion) profoundly modifies the prognosis of the disease and so should allow soon a multidisciplinary therapeutic discussion.