Our surgical experience in foramen magnum meningiomas: clinical series of 11 cases

Introduction We aimed to discuss surgical approaches and results that we applied foramen magnum meningiomas. Methods We retrospectively investigated 11 foramen magnum meningioma cases, who had been operated between the dates of February 2012 and March 2017. Results Eight of the patients were females and 3 of the patients were males, the age range was 32-75 and the age average was 60.8. 5 of the tumors were anatomically localized as posterolateral, 2 of them were localized as anterolateral, 2 of them were localized as lateral and 2 of them were localized as anterior according to the brain stem or spinal cord. Posterior far lateral (4 patients) approach including C1 laminoplasty (7 patients) and 1/3 condyle resection was surgically applied to the patients with median suboccipital craniotomy. Gross total excision was applied to 82% of the patients (9 patients) and subtotal mass excision was applied to 18% (2 patients) of the patients. The most frequent post-operative complications were temporary lower cranial nerve (CN IX and X ) palsy in our 2 anterior localized cases (18%) and also cerebrospinal fluid (CSF) fistula in our 1 anterior localized case with difficulty in swallowing (dysphagia). Karnofsky scores of the patients, who were followed for 18 months in post-operative 12 and 48 months of average, in the last follow-up were 80 and no post-operative mortality occurred. Conclusion Posterior midline suboccipital and far lateral approaches that we apply in our own series were appropriate approaches for foramen magnum meningiomas.


Introduction
Meningiomas are generally benign, and they are the tumors with good prognosis. Foramen magnum meningiomas constitute 1.8-3.2% of all meningiomas [1][2][3][4]. They are observed more frequently in fifth and sixth decades [5][6][7][8]. Their surgical methods are quite difficult and complex as they grow by pushing forward the important vascular structures such as lower cranial nerves and vertebrobasilar complex [3,5,6,[8][9][10]. Joint stability between occipital bone, 1 st cervical spine (C1) and 2 nd cervical spine (C2) may be lost since they may cause craniocervical junction bone anatomy changes as they grow silently [7,10]. They are frequently reaching to large sizes when they are diagnosed ( Figure 1). We primarily used posterior suboccipital craniotomy and C1 laminoplasty as a surgical approach and secondly far lateral approach including condyle resection for tumor resection in our study. We attempted to discuss the surgical approaches we apply and the results of these approaches on the rates of tumor removal by presenting our experience related to foramen magnum tumors in the last 7 years.

Methods
Surgical treatments were applied to 11 (Figure 2). Pre-operative karnofsky performance scales (0-death 100-very good health) were used in order to evaluate the life quality of the patients and visual analog scales (0-no pain, 10very severe pain) (VAS) were used in order to rate the neck pains.
Complete removal of tumor with its capsula was evaluated as gross total tumor excision in our study. Karnofsky and VAS were repeated for our post-surgery results. 72.7% (8 patients) of 11 cases were females and 27.3% (3 patients) were males. Age ranges were 32-75 and age average was 60.8. The start of the symptoms was 14 months in average between 6 and 36 months. The start complaint and symptom were headache and neck pain, and they were observed  Table   1.
5 (46%) of them were localized posterolateral, 2 (18%) of them were localized anterolateral, 2 (18%) of them were localized lateral, 2 (18%) of them were localized anterior ( Table 2). While posterior median suboccipital craniotomy and C1 laminoplasty were made to 7 patients (64%) in total with posterolateral and lateral localization, posterior far lateral approach including 1/3 condyle resection was applied to 4 patients (36%) in total with anterolateral and anterior localization. While gross total mass excision was made to 9 patients (82%), subtotal mass excision could be made to 2 patients (18%) with anterior localization due to cohesion of tumor to cranial nerves (IX,X) and vascular structures ( Table 2)

Discussion
The appropriate one from anterior, anterolateral, posterior, posterior far lateral and lateral surgical approach forms is performed on foramen magnum lesions. Surgical interventions to this region are risky in terms of morbidity and mortality [11,12]. approach [1,16,20,22,23]. Lumbar drainage was started to be applied due to CSF leakage from the wound site on 5th day of post-operative period in 1 case with anterior localization, to whom we performed tumor excision with far lateral approach. CSF leakage was ceased without needing a second surgery by two weeks of follow-up by lumbar drainage. It is reported in various series that CSF fistula is frequently observed in the cases, to whom far lateral approaches are applied [1,8,9,22,23]. Posterior median surgery approach is a safe and effective method for foramen magnum meningiomas, and it is an approach recognized and well-known by the surgeons. There is no need for excision of condyle or lateral mass in this approach. Postoperative recovery is fast. While occipitocervical fusion is rarely needed in posterior approach, fusion between 0% and 66% may be needed in occipital condyle resection in far lateral approach [18, 21,24]. Post-operative 50% rate of instability may develop in craniocervical intersection made on one side and condyle excisions more than 1/3 and occipitalcervical fusion may be needed [2]. Surgery made by combining C1 laminectomy to posterior midline suboccipital approach in posterior or posteriolateral localized tumors is an appropriate approach for these region tumors [6,25].
Sohn et al. [8] combined midline suboccipital craniotomy and C1 laminoplasty into all cases only with ventral localized foramen magnum in 11 cases of study in 2013. At the same time, they reported that posterior approach will be insufficient and applying far lateral approach will be more correct in the cases, which were thought to have quite high tumor vascularity. We applied this application, which was very rare in literature and performed by Sohn et al. [8]  What is known about this topic  Surgical removal of the masses located on the anterior site is difficult; morbidity and mortality rates are higher;  Posterior median surgery approach is a safe and effective method for foramen magnum meningiomas, and it is an approach recognized and well-known by the surgeons.

What this study adds
 Suboccipital craniotomy bone which was repositioned with mini-plate and mini-screw and C1 laminoplasty may prevent excess bone loss; a positive cosmetic appearance may be achieved and cervical instability may be prevented.

Competing interests
The authors declare no competing interests.

Authors' contributions
All the authors have read and agreed to the final manuscript.