Nasal dermal sinuses and cysts.

Nasal dermal sinuses and cysts are best detected by careful clinical inspection of the face for tiny ostia or widening of the nasal bridge and by detailed radiologic evaluation of the nasal bones, nasal septum, crista galli and falx. The sinus tracts may remain superficial to bone, extend partway into the nasal septum or pass far posterosuperiorly beneath the nasal bones, through the foramen cecum, and anterior to or through a bifid crista galli to lie between the leaves of the anterior falx. Glabellar sinuses may pass through the midline frontonasal suture to the foramen cecum, crista galli and falx. These courses correspond to embryonic midline diverticula of dura (with or without arachnoid and brain tissue) that protrude into a) the fonticulus nasofrontalis and b) the prenasal space situated behind the nasal bones and in front of the nasal capsule, occasionally reaching the surface ectoderm. Persistence of variable portions of these diverticula results in the clinical spectrum of nasal sinus tracts, fibrous cords, interposed (epi)dermoids, meningoceles, encephaloceles and 'gliomas'.