Encephalocele Basal encephalocele 2012-04-29T09:14:34Z UMLS:C4023176 Basal encephalocele is an encephalocele that occurs along the cribriform plate or through the sphenoid bone. The mass may appear in the nasal cavity, nasopharynx, epipharynx, sphenoid sinus, posterior orbit, or pterygopalatine fossa. The important distinction from other types is that no external tumor is visible except in those rare instances of herniations so large that they protrude through the mouth or nares. HP:0011817 The skull base is made up of the ethmoid, sphenoid, occipital, paired frontal, and paired parietal bones, and is subdivided into 3 regions: the anterior, middle, and posterior cranial fossae.