| Part I Microsurgical anatomy and radiology of the retrosigmoid-suprameatal approach:Objectives: To discuss the relationship between the anatomical variations and the safety of petrous bone drilling in the retrosigmoid-suprameatal approach and define the maximal range of petrous bone drilling and its relevant factors. Methods: Bony structures of petrous apex were observed and measured on 15 dry skulls. 15 wet skulls were dissected stepwisely to show the vascular,neural and membraneous structures around the tentorial notch,CPA,petroclivus and the middle cranial fossa. Distances between important structures,lengths of cranial nerves and diameters of main blood vessels were measured. CT and MR scans of 15 cadaveric heads were obtained and angles formed by the tentorium and medial aspect of petrous bone,horizonal level and trigeminal nerve were measured and differences between bilateral sides were statistically analysed .The longitudinal distances between the superior wall of carotid canal and superior wall of internal auditory meatus, superior border of VII,VIII cranial nerves were also measured.Results: The distance between the suprameatal tubercle and the petrous apex,posterior wall of carotid sulcus,medial wall of carotid canal, junction of the arcuate eminence and the petrous ridge was 3.27±1.61mm , 5.57±1.85mm, 8.21±1.95mm and 8.37±2.68mm,respectively.In 4 sides,the original part of the medial border of Meckel cave was found closely related to C5,while close relationship between the medial border of Meckel cave and the cavernous segment of abducent nerve was observed in 3 sides. The angle formed by the tentorium and the medial surface of petrous bone,the horizonal level and the trigeminal nerve on coronal CT/MR scan was 88.4±12.8 degrees, 43.2±8.0 degrees and 23.6±7.7 degrees respectively and no significant difference was found between bilateral sides(P> 0.05).The superior wall of internal auditory meatus and the superior border of VII,VIII cranial nerves were always above the superior wall of carotid canal with a longitudinal distance of 5.13 ± 1.70mm and 3.29±1.65mm Respectively. Conclusions: The anatomy of petrous apex varies individually.The risk of C5 and abducent nerve injury due to surfficent exposure of the medial border of Meckel cave is about 10% via the retrosigmoid-suprameatal approach.C6 will not be injuredbecause petrous bone drilling is limited inferiorly by VII.VIII cranial nerves.With dislocation of the transverse sinus and drilling of the upper part of the anterior wall of the internal auditory meatus,the petrous bone can be maximally drilled away and middle cranial fossa maximally exposed.Part II The study on the indicatons and intraoperative anatomical landmarks of the retrosigmoid-suprameatal approachObjectives: To verify the results of the microanatomical and radiological studies and define the indicatons and intraoperative anatomical landmarks of the retrosigmoid-suprameatal approach and discuss the effect of the endoscope in this approach.Methods: 30 suprameatal tubercles were drilled via the retrosigmoid-suprameatal approach on 10 embalmed and 5 fresh cadaveric heads.The size of the bone window and its distances to important structures were measured from the middle cranial fossa.The middle cranial fossa outside the bone window was explored with the rigid endoscope to learn the extent of added exposure. Coronal CT scans were obtained after the mimic operation and relationship between the bone window and C6 was observed.Results: After drilling of the suprameatal tubercle,part of the bottom of Meckel cave and the dura of middle fossa lateral to Meckel cave could be exposed.The structures outside the bone window could not be seen under the microscope.With help of the endoscope,the site where mandibular branch of the trigeminal nerve enters the porus ovale could be reached.The bone window of the middle fossa was rhomboid-shaped whose anterior,posterior,medial and lateral side was 6.91±1.34mm, 16.29±2.24mm, 21.94±2.22mm and 13.01±2.91mm long,respectivel...
|
PDF Full Text Request