The Coronal Aeration Of The Sphenoid Sinus And It' S Effects On The Expanded Endoscpic Endonasal Skull Base Surgery Related Anatomic Landmarks : A Computed Tomography Study

Objective: To explore aeration of sphenoid sinus on the coronal plane with novel designed classification system on the high resolution computed tomography (CT) scan, and to study the effects of different degree of coronal aeration on the expanded endoscpic endonasal skull base surgery related anatomic landmarksMethods: 155 patients without sinonasal malignancy or facial fractures were selected. Their ages were between 18~78 years, male 106 cases and women 49 cases. The scannings were performed with a Light Speed CT machine in a helical mode with a slice thickness of 0.625mm, and were reformatted into the coronal and axial planes with 0.5 mm spacing. For each patient, we obtained measurements from both the right and left sides using Centricity DICOM Viewer 3.0 radiographic software in both the axial and coronal planes. Aeration of the sphenoid sinus does not extend laterally beyond the imaginary line extended vertically on the base of the medial pterygoid plate defined as degreeⅠ, aeration locates between the imaginary lines extended vertically on the base of the medial pterygoid plate and the lateral pterygoid plate defined as degreeⅡ, aeration extends laterally beyond the imaginary line extended vertically on the base of the lateral pterygoid plate defined as degreeⅢ. we measured twelve morphometric parameters in the coronal plane and six morphometric parameters in the axial plane. These parameters of different planes were related to surgery of transpterygoid middle cranial fossa approach and petrous apex approach respectively. The SPSS version 16.0 was used,one-way analysis of variance (ANOVA) and Non-parametric rank sum test (P<0.05).Results: Among 310 sides, degreeⅠpneumatization in 43%, degreeⅡpneumatization in 34%, degreeⅢpneumatization in 23%.In the coronal plane, there were statistical differences in seven morphometric parameters when pneumatization varied; in the axial plane, there were statistical differences in three morphometric parameters when pneumatization varied .The average distance between the base of the medial and lateral pterygoid plate was 6.31mm (1—11.35mm), the distance was 6.20±1.83mm in the degreeⅠpneumatization group,6.48±1.53mm in the degreeⅡpneumatization and 6.27±1.56mm in the degreeⅢpneumatization. Amomg the different pneumatizations groups, there was no statistical difference(X2=0.826,P=0.439). The average distance from the vidian canal to foramen rotundum was 6.39mm(1.6—15.3mm),the distance was 4.99±1.6mm in the degreeⅠpneumatization group, 6.28±2.13mm in the degreeⅡpneumatization group and 9.24±1.89mm in the degreeⅢpneumatization group. There were statistical differences amomg the different pneumatizations(X2=123.108,P=0.000). The area circled by the vidian canal, the foramen rotundum, the base of the medial and lateral pterygoid plate,was 88.21 mm2 (9.31—232.13 mm2),75.53±27.42mm2 in the degreeⅠpneumatization group,83.04±31.03mm2 in degreeⅡpneumatization and ,120.33±42.65mm2 in theⅢdegree pneumatization.There were statistical differences among the different pneumatizations(X2=45.407,P=0.000). Among the different coronal sphenoidal sinus aeration, the degrees of pneumatization relative to the circumference of the vidian canal and the foramen rotundum were statistical difference(sH=137.314,P<0.01;H=163.204,P<0.01).Conclusions: The medial and the lateral pterygoid plate and their bases have different embryonic origins from sphenoid body and wings, Which can be recognized as a constant landmarks of coronal sphenoidal aeration as well as expanded endoscopic skull base surgery. The variations of the sphenoid sinus pneumatization could have effect on the transpterygoidal approach to the petroclival region and middle cranial fossa. This study revealed that regularity of the pneumatized variations and it's effects on the landmarks may guide clinical practice.