The suboccipital midline approach to foramen magnum meningiomas: safety and efficacy in a series of 23 consecutive patients over a 5-year period

Abstract

Dear Editor, We appreciated the Editorial BThe suboccipital midline approach to foramen magnum meningiomas; feasible, but is it optimal?^ by Dr. Dehdashti [1] about the paper we recently published on Acta [2]. We would like to take this opportunity to reply to the author, providing readers with required additional clinical data. We are obviously unable to answer the question asked by Dr. Dehdashti because a specifically designed study to address this issue is not currently available in the literature. As encouraged by the author, we revised the outcome of 23 consecutive patients undergoing resection of a FM meningioma via a midline suboccipital (MSO) approach over the last 5 years at our department. Overall morbidity and mortality rates were 8.7 % and 0 %, respectively. At 3 months after surgery, eighteen (78.2 %) patients improved, four (17.3 %) were stable, and one (4.3 %) worsened. Four (17.3 %) patients presented a transient postoperative deficit of IX–X cranial nerves. No patient presented a postoperative XII cranial nerve deficit. One patient (4.3 %) presented a postoperative CSF fistula that spontaneously resolved over 2 months. The tumor size ranged between 19 and 34mm. GTR (Simpson grade I and II) was achieved in 100% of cases. The mean hospital stay was 16 days (range, 9–37 days). Published literature on MSO approach for FM meningiomas reports similar data [4, 5]; these series are all about meningioma of small to medium size. In this sense, we suppose that it could be misleading to state that the MSO approach is more adequate for larger FM meningiomas. In an interesting review on the far lateral (FL) approach for FM meningiomas, Flores et al. [3] recently reported an overall morbidity and mortality rate of 30 % and 0–3 %, respectively. Post-operative IX–X and XII deficit rate was 44 and 33 %, improving over time in 66 % of cases. CSF fistula was reported in 16–20 %. With regard to preoperative status, 80.6 % improved, 6.7 % was stable, and 9.1 % worsened. GTR (Simpson grade I and II) was reported in 70–96 % of cases. Some intraoperative considerations are needed to compare MSO and FL approaches in this specific setting. Meningiomas located in the region Banterior^ to the brainstem, in the region of the foramen magnum, are only rarely strictly anterior (two cases in our series); the large majority of tumors pointed laterally on one side of the midline, and the brainstem was displaced posterolaterally rather than posteriorly. This aspect has already been described by other authors [4]. The dural attachment is usually just medially located to the site of vertebral artery (VA) entry. Thus, when approaching an FMmeningioma via anMSO approach, the tumor devascularization is easy and safe to perform. The brainstem, cranial nerves, vertebral artery, and tumor are exposed in the same field, and the dissection can be performed with visualization of all structures. The exposure is wide and not deep and it can easily be improved (when needed) from a lateral perspective by the use of an appropriate angulation of the microscope (as shown in our paper). The vertebral artery is exposed easily in the region of the arch of atlas at the site of its entry into the dura by a midline approach. However, the suggested two-step (before and after dural opening) removal of C1 allows a tailored bone resection and a safer VA exposure and control. Dural and wound closure with an MSO approach is easy and safe, and it avoids the possible difficulties described in the lateral and anterior approaches. The brainstem manipulation, when needed approaching smaller and more anterior FM meningiomas, as in the * Alessandro Della Puppa alessandro.dellapuppa@sanita.padova.it