Significance of Cerebral Venography in Surgery of Petroclival Meningiomas

ABSTRACT

OBJECTIVE: A thorough understanding of the related venous structure is mandatory for successful removal of the petroclival meningiomas. This study was planned to investigate the guideline for safe ligation and incision of transverse or sigmoid sinuses and the importance of drainage pattern of vein of Labb in surgical removal of petroclival meningiomas. MATERIALS AND METHODS: The authors reviewed the venogram of the consecutive 37 cases of petroclival meningiomas and retrospectively analyzed their surgical findings. The drainage pattern of confluence of Herophili was classified as Type A(confluent and equal on both sides), Type B(confluent and non-dominant on tumor side), Type C(confluent and dominant on tumor side) and Type D(unilateral drainage only) as these findings gave the information on safe ligation and resection of the sinus. Usefulness of intraoperative test clamping of sinus for safe ligation was also reviewed. The vein of Labb was analyzed with respect to its draining point and its collaterals to other superficial veins. RESULTS: Contraindications of the sinus ligation and resection according to the drainage pattern at the confluence of Herophili were Type C(n=10, 27%)and Type D(n=4, 11%). Patients with Type A(n=12, 32%)and Type B(n=11, 30%) were tolerable to sinus ligation ipsilateral to tumor, if the test clamping proved to be safe. Identification of no brain swelling, after intraoperative test clamping of the sinus for more than 30 minutes performed in 7 out of 11 cases, was a reliable indicator of safe sinus ligation. The drainage pattern of the vein of Labb, especially low-lying type, could predict the possibility of postoperative hemorrhage and infarction. Its drainage into tentorium or superior petrosal sinus, however, made the transtentorial approach impossible, leading to restricted operative field. CONCLUSION: For a successful removal of the petroclival meningiomas preoperative venogram should be examined carefully. The extent of exposure in a planned approach can be estimated by analyzing the variation of sinuses and the drainage pattern of vein of Labb.