[2 modalities in the embryogenic process of frontonasal cysts and fistulae]

The two principal embryogenic theories, persistence of residual structures remaining after closure of the anterior neuropore and inclusion of epiblastic derivatives in the prenasal space, may be combined, with resulting two embryonic varieties of these malformations. Glabellar cysts, with or without fistulae extending them downwards, and which remaining at superficial level may perforate the true nasal bones. Other fistulae can develop which extend deeply and present variable dilatations with a more or less oblique path upwards depending on the level of their opening into the nose.