The shape of the anterior part of the anterior cranial fossa undergoes impo
rtant changes in the postnatal life depending on the degree of pneumatisati
on of the ethmoid labyrinth and/or the frontal sinus. There exist three pos
sibilities in these relations: 1) From the newborn period up to 9 years of
age, in the majority of the cases the cribrous plate is situated at the lev
el of the roof of the ethmoid labyrinth with the width of the ethmoid incis
ure corresponding to the width of the cribrous plate. 2) In the period from
9-35 years of age, in the majority of cases, the ethmoidal cells are partl
y or completely incorporated into the floor of the anterior cranial fossa w
ith the width of the ethmoid incisure corresponding to the number of cells
forming the floor of the anterior cranial fossa. 3) Tn the period from 35-8
0 years of age, the cribrous lamina is in the majority of cases lowered due
to the intensive development of the frontal sinus. The medial wall of the
ethmoid labyrinth consists of a thin bony strip, the width of which depends
upon the degree of lowering of the cribrous plate. Adequate CT imaging may
clarify the situation.