A clinical anatomical study on identification of the internal auditory meatus in middle cranial fossa approach

OBJECTIVE The head of malleus (HOM) was regarded as the landmark for the middle cranial fossa approach,and its relationship with internal auditory meatus(IAM) was measured. The purpose of this study was to find a safe method to locate IAM. METHODS Twelve heads of adult cadaver fixed with 10 % formaldehyde (23 sides) were microsurgically dissected from the middle cranial fossa approach. The foramen spinosum,Ferrein's foramen,greater petrosal nerve,lesser petrosal nerve,facial nerve,HOM,arcuate eminence,superior petrosal sinus,semicircular canal,and IAM were exposed. First,blue lines method was used to locate IAM. Second,HOM as the landmark was used to locate IAM. RESULTS The angles between the SSC and the longitude axis of IAM are 58.52°±4.84°。 A perpendicular line (AB) was drew from the center of HOM to the longitude axis of the temporal bone (the longitude axis of the superior petrosal sinus),line BC was drew from the anterior 30°(28.93°± 6.07°) to the line AB. On the line BC,fundus of IAM can be located (6.69±1.10) mm medial to HOM,the center of the internal acoustic pore can be located (20.1±1.48)mm medial to HOM. CONCLUSION In the middle cranial fossa surgery,HOM can be used to locate IAM and its surroundings structures when traditional landmarks are unrecognized.