[Surgical anatomy of the so-called dangerous frontal sinus (Boenninghaus)]

Surgically dangerous type of frontal sinus was first reported by Boenninghaus in 1923. The present study concerns with the types and incidence of the dangerous frontal sinus as investigated by axial scans of HRCT. A total of 286 adult and 33 infant cases was included. The anterior end of the olfactory groove was first classified into three types, i.e., normal type, obliterated type (obliterated by cancellous bone) and dangerous type (with Recessus cristae galli and Torus olfactorius). In the adult, the incidences of these types are, 67.2, 18.5 and 14.3%. In the infant, incidences are 42.4, 51.5 and 6.1%. In the adult, the incidences do not differ in sex and sides. The dangerous type was classified into moderate and severe according to the depth of Recessus cristae galli, those with 1.5-2.9 mm depth are moderate and those over 3.0 mm are severe. The moderate dangerous type was seen in 30 sides and severe in 46 sides. In addition to the depth of Recessus cristae galli, distances from Torus olfactorius to the anterior sinus wall and the frontal skin surface were also included. These distances tend to be larger in male.