Quantitative Analysis of the Effect of Brainstem Shift on Surgical Approaches to Anterolateral Tumors at the Craniovertebral Junction

Object: Some authors have reported that most anterior and anterolateral tumors at the craniovertebral junction (CVJ) can safely be resected using a simple posterolateral approach given the surgical corridor afforded from brainstem shift by the pathological lesion. The purpose of this study was to study how increasing anterolateral CVJ tumor size affects exposure in the posterolateral and far lateral approaches.

Methods: Six embalmed cadaver heads were used. A posterolateral approach was performed on one side and a far lateral with ⅓ condyle resection on the contralateral side. Clival and brainstem working area and surgical freedom were measured. A balloon catheter was filled to pre-determined volumes to simulate 10, 15, and 20mm anterolateral mass lesions and measurements were repeated after each size lesion and compared using a paired t-test.

Results: Mean clival area was significantly greater with the far lateral approach (197.4 vs 135.0mm2, p = 0.03) with no mass lesion. There was no significant difference in clival working area with the far lateral approach for 10mm (246.8 vs 237.9mm2, p = 0.785), 15mm (306.7 vs 262.4mm2, p = 0.249), and 20mm (360.0 vs 332.7mm2, p = 0.636) mass lesions. Mean brainstem working area was significantly greater with the far lateral approach for 0mm (127.8 vs 65.8 mm2, p = 0.003), 10mm (129.5 vs 87.5 mm2, p = 0.045), and 15mm (140.1 vs 97.8 mm2, p = 0.011) mass lesions. There was no difference at 20mm (146.7 vs 147.8 mm2, p = 0.969). Medial-lateral surgical freedom was greater with the far lateral approach for all size lesions (19.0° vs 12.8°, p = 0.008, 22.3° vs 17.6°, p = 0.148, 30.7° vs 21.5°, p = 0.021, 35.8° vs 30.7°, p = 0.241), but only reached significance at 0 and 15mm mass lesions.

Conclusion: Clival working area was significantly greater for the far lateral approach, but this difference disappeared for mass lesion 10mm or greater. Brainstem working area was significantly greater with the far lateral approach, but this difference disappeared at a mass lesion size of 20mm. This is the first study in the literature quantifying how tumor shift can affect surgical exposure in comparative approaches. The results of this study provide insight on one important variable in the decision-making process to select the optimal approach for anterolateral CVJ tumors.