Venous Anatomy Related To Surgical Approach In Posterior Cranial Fossa

Objectives Surgery for space-occupying lesions in the posterior cranial fossa is very difficult.Subtentorial supracerebellar approach is a routine neurosurgical approach.In order to obtain more operation space,it is often necessary to sacrifice some veins.Whether the cerebral venous reflux is blocked after operation depends on the extent of bridge vein injury and the development of the collateral branch of venous sinus communication.In addition,the injury of venous struture during the approach can also lead to intraoperative hemorrhage.Therefore,preoperative evaluation of venous anatomy in posterior cranial fassa,including bridging veins,smll venous sinuses and emissary vein,is very important,which is helpful to design appropriate surgical approaches.Therefore,the aim of this study is to explore the abitity of imaging detection techniques to evaluate the venous anatomy of the posterior fossa,focusing on the guiding significance of venous anatomy for the surgical approach.Methods 1.Bridging veins in posterior cranial fossa: A total of 20 human cadavers(40 sides),12 fetal human cadavers vascular casting and 62 patients(120 sides)were examined in this study.Each head of the cadavers was injected with blue-coloured latex via the superior sagittal sinus and internal jugular veins.The venograms of each patient was obtained from the venous phases of digital subtraction angiography(DSA)(40sides out of 22 patients)or computed tomographic venography(CTV)(40 sides out of20 patients)or magnetic resonance venography(MRV)(40 sides out of 20 patients).The number,diameter and distribution of posterior fossa bridging veins were compared among different examinations.2.Small venous sinues in posterior cranial fossa: A total of 50 patients who underwent contrast-enhanced CT with a multidetector scannerwere retrospectively reviewed.Axial and reconstructed images were evaluated by two neuroradiologists and a anatomical expert.The occurrence rate,diameter of small venous sinuses and their relationship with adjacent vessels were observed.3.Emissary vein in posterior cranial fossa: A total of 100 consecutive patients were evaluated by helical CT in bone window mode reconstructed using the standard technique(4.5-mm slices)and the highresolution technique(1 mm)for the posterior fossa.The difference of the existence,size and location of the emissary veins between the two methods was evaluated.Results 1.Bridging veins in posterior cranial fossa: Compared to the cadavers,DSA,CTV and MRV revealed 89%,40% and 38% of the cerebellar bridging veins because the veins depicted by the imageology were 11%,17% and 33% larger than that of the cadavers.The cerebellar bridging veins entered into transverse sinus and superior petrosal sinus either directly or indirectly via tentorial sinus.The lumen of the tentorial sinus was flattened,and discontinuity,weaken or intensive signal was often observed on neuroimagings.The dural entrence of cerebellar bridging veins were clustered along the medial end of transverse sinus,the tentorial sinus and the anterior segment of the petrosal sinus.2.Small venous sinues in posterior cranial fossa: The venous structures contributing to craniocervical junction venous drainage,including the inferior petrosal sinus,marginal sinus,suboccipital cavernous sinus,and condylar veins were well depicted in all cases.The occipital sinus was identified only in 18 cases.The IPS showed variations in drainage to the jugular vein through the jugular foramen or intraosseous course of occipital bone via the petroclival fissure.The diameter of each vein structure varies greatly in different individuals.3.Emissary vein in posterior cranial fossa: In different individuals,there are significant anatomical variations in the number,size and length of the emissary veins.The detection rate of the catheter veins in thin-slice spiral CT scan is significantly higher than that in conventional CT scan.Conclusion 1.In general,the paramedian infratentorial approach has lest chance to damage the bridging veins in posterior cranial fossa.The preoperative venogram is useful to design the individualized surgical approach for the preservation of bridging veins below the tentorium.2.The anatomy of venous sinuses in the posterior fossa varies greatly.Understanding these differences is of great significance for the diagnosis and treatment of skull base diseases.Preoperative enhanced CT scan can evaluate the anastomosis of venous sinuses in the posterior fossa.3.Thin-slice spiral CT is better for posterior cranial fossa surgery,which can determine whether the emissary vein is existed and its course,so as to reduce the occurrence of intraoperative hemorrhage.