Lower third clivus and foramen magnum intradural tumor removal: The plea for a simple posterolateral approach

Far Lateral Approach: "Trans-tumor Approach" on Huge Dumbbell-Shape Neurofibroma of Anterior Foramen Magnum Without Craniectomy-Anatomical Consideration and New Trend

The foramen magnum approach is always challenging because of the relationships between vital neurovascular structures in this area. Several approaches have been described, among them, the far lateral approach remains a cornerstone for the resection of anterior or anterolateral processes of the foramen magnum. This approach displays two main steps: the first is cervical, whereas the second is cranial.We report the case of a 63 year-old woman admitted for a progressive quadriplegia with swallowing disorders revealing a process of the anterior and anterolateral part of the foramen magnum. A cervical step of a far lateral approach without opening the foramen magnum achieved a near total resection of the process via a trans-tumor corridor and confirmed a dumbbell shape neurofibroma. The postoperative period showed a resolution of swallowing disorders and a progressive improvement of muscular strength. At 8 months follow-up, she was asymptomatic and able to walk with a normal balance. The surgical technique and anatomical correlation of this trans-tumor approach are discussed.

Comparative analysis of surgical exposure and freedom between the subtonsillar, endoscope-assisted subtonsillar, and far-lateral approaches to the lower clivus: A cadaveric study

The far-lateral (FL)approach is a classic technique for skull base surgeries involving the lower clivus (LC).Recently, a modified suboccipital midline approach known as the subtonsillar (ST) approach, along with the endoscope-assisted subtonsillar (EST) approach, has been described as a minimally invasive technique to treat LC lesions. However, there is no quantitative study on comparing these approaches together for reaching LC. We aimed to compare surgical exposure and freedom provided by ST, EST, and FL approaches for various targets at LC. These approaches were performed on each side of five cadaveric specimens (total 10 sides), and relevant parameters were quantified and compared using a repeated measures ANOVA test. FL approach yielded the greatest surgical area (237.8 ± 56.0 mm²) and exposure, including lengths of glossopharyngeal nerve (16.2 ± 1.9 mm), hypoglossal nerve (11.4 ± 2.4 mm), vertebral artery (23.9 ± 3.3 mm), followed by EST and ST approaches. For surgical freedom, FL approach provided the greatest angle of attack (90.0 ± 14.0° at jugular foramen, 95.1 ± 15.8° at hypoglossal canal, 83.4 ± 31.4° at bifurcation point of posterior inferior cerebellar artery and vertebral artery). Our systematic comparison suggests that EST approach, compared to ST approach, can significantly increase surgical exposure to the medial side of LC, but FL approach still provides the greatest surgical exposure and freedom at LC. Despite the limitations of a cadaveric study, our quantitative data can update the literature on currently available surgical techniques for reaching LC and better inform preoperative planning in this area. Further studies should be performed to evaluate these approaches in clinical practice.

Gridding Microsurgical Anatomy of Far Lateral Approach in the Three-Dimensional Model

OBJECTIVE

The far lateral craniotomy involves osteotomy of various portions of occipital condyle. Intracranial operation exposing clivus encounters complicated neurovascular anatomy. The aim of the present study was to make refinement for the anatomy of far lateral approach by gridding route in the 3-dimensional model.

METHODS

Computed tomography and magnetic resonance imaging data were used to construct 3-dimensional model containing osseous and neurovascular structures of skull base. Then, far lateral approach was simulated by triangular prism and divided into gridding surgical route. The relationship of surgical route and osseous and neurovascular structures was observed. Measurement of volume was performed to evaluate surgical exposure.

RESULTS

Observation of 3-dimensional model showed bony drilling of far lateral approach started with the occipital condyle and passed through the lateral edge of foramen magnum. The cerebellum and medulla oblongata were exempted from the surgical route exposing clivus. The anatomy variances of operative space, osseous, and neurovascular structures in the gridding route were displayed clearly and compared objectively.

CONCLUSION

The gridding operative spaces for the far lateral approach are useful to disclose the detailed discrepancy in the different surgical region. The volumetric measurement provides quantified information to facilitate a better understanding of the anatomy variance.

Prognostic factors affecting the surgical outcome of anterolateral benign tumors in the foramen magnum region

INTRODUCTION

Anterior and anterolateral tumors in foramen magnum region are rare and surgically challenging although most of them are benign. The optimal approach is debatable and prognostic factors affecting surgical outcome remains unclear. We aimed to identify factors including surgical approach determining postoperative outcome.

METHODS

The data of 49 patients diagnosed benign tumors involving the anterior and anterolateral foramen magnum were retrospectively analyzed in our institution from January 2009 to January 2015. The demographic, clinicoradiological, surgical and follow-up information were collected. Primary surgical outcome was new neurological deficits. A multivariate analysis was performed to determine predictors of postoperative neurological deficits.

RESULTS

Patients were operated on either via suboccipital (31 cases, 63.3%) or far lateral (18 cases, 36.7%) approach. Newly developed neurological deficits occurred in 11 (22.4%) patients, improved over time in 6 (12.2%) patients. 2 (4.1%) patients died within 3 month after operation and 2 (4.1%) suffered tumor recurrence. 44 (93.6%) out of 47 survivors had good functional outcome (postoperative Karnofsky performance score ≥80) at last follow-up period. Patients with postoperative new neurodeficits harbored tumors which tended to more frequently involve lower third clivus (p = 0.083), to be meningiomas (p = 0.059), were more likely to be removed through far lateral approach (p = 0.010) and have extradural extension (p = 0.024). Multivariate analysis showed that the far lateral approach was the sole predictor independently related to postoperative neurological deficits (p = 0.029).

CONCLUSIONS

The far lateral approach to benign tumors anterolateral to foramen magnum experienced higher rate of immediate new neurological deficits compared to suboccipital approach. The role of the suboccipital approach may be underestimated and should be further evaluated.