Management of Intradural Anterolateral Meningiomas of the Foramen Magnum with the Posterolateral (Far-Lateral) Retrocondylar or Partial Transcondylar Approach: Learning from Experience in 26 Consecutive Cases
Objective: To evaluate retrospectively our surgical technique and results in the management of anterolateral foramen magnum (FM) meningioma with the posterolateral (far-lateral) retrocondylar or partial transcondylar approach, and to adapt our prospective management regarding surgical indication, epidural transposition of the vertebral artery (VA), drilling of the occipital condyle, and extent of tumor resection. Methods: From 1992–2008, 16 women and 10 men (ages 28–82 years) were referred for anterolateral FM meningiomas (10 anterior, 16 lateral). All patients were symptomatic, and all meningiomas inserted at C0 (FM rim); they extended to the clivus in 4 patients, to the cervical canal in 10, and to both in 12. The tumor was located above the VA in 7 cases, below in 9, and on both sides in 10 (Lariboisière classification). Twenty-two patients were operated on using the posterolateral (far-lateral) transcondylar approach described by Bertalanffy and Gilsbach in 1996, which included: C1–C3 laminectomy; occipital hemicraniectomy; C1 transverse foramen opening; medial epidural VA exposure and transposition (in 19 of 22 cases); and partial (from one third to one half) drilling of the occipital condyle (in 10 of 22 cases), with the amount of drilling depending on the position of the meningioma on the FM rim and the wish to reach the very anterior pole of the tumor. We analyzed: (1) surgical indications; (2) utility of VA transposition and condyle drilling; (3) quality of access and view; (4) microsurgical technical difficulties according to tumor location, extent, and consistency; (5) microsurgical challenges at the tumor to spinal cord, cranial nerves, and vessels interface; and (6) morbidity and total removal rate. Results: Four patients older than 70 years were not operated on (3 had only a few symptoms, and 1 had an enormous tumor), and their follow-up at 2–3 years showed stable clinical status. Operatively, VA transposition (in 19 of 22) enlarged the access, but it was only helpful for accessing the lower clivus and intradural VA anteriorly. Condyle drilling of up to 50% did not induce instability and enlarged the intradural view to the anterior FM rim, but it did not improve tumor dissection and removal; therefore, systematic drilling decreased with experience and was only kept for small anterior meningiomas. Total removal was achieved in 16 of 22 (73%). We learned from experience that tumor consistency (calcified and fibrous meningiomas generally lengthened dissection), VA encasement (inclusion/stretching of VA), and tumor invasiveness (adherences to cranial nerves) represented prognostic factors increasing complications (1 death, 5 permanent deficits). Conclusion: Our study illustrates that the posterolateral (far-lateral) transcondylar approach with VA transposition offers a large view to accurately manage the anterior FM rim and lower clivus. With surgical experience, however, we learned to: (1) measure indication according to age and severity of symptoms; (2) consider the transcondylar approach in anterior cases only, although it neither significantly improved our surgical results nor induced instability in our series; (3) consider the retrocondylar approach as sufficient for lateral meningiomas.