Anatomic Factors Affecting Size of Suboccipital Decompression

Abstract

Abstract INTRODUCTION Emergent suboccipital decompressions are not uncommon procedures for the management of cerebellar infarcts and hemorrhages with mass effect. While anatomic landmarks, such as the transverse sinus and foramen magnum, provide clear boundaries to the decompression, there are a multitude of patient-specific anatomic factors that complicate positioning, and make obtaining an adequate decompression challenging. METHODS We reviewed a consecutive series of patients undergoing emergent suboccipital decompressions. Patients in whom a unilateral decompression was performed were excluded from the study. A total of 43 patients met the inclusion criteria, and were further reviewed. The primary outcome was to determine what anatomic factors predicted maximal width and cranial-caudal extent of SOC bone flap. Head CTs, including scout film radiographs, and chest XRs in the pre- and perioperative period were reviewed to measure specific anatomic features. RESULTS The average patient age was 55 (19-85). 34% of patients were female. A bivariate analysis showed that AP diameter correlated to inion-to-foramen magnum distance (P = .001, r2 = 0.501), shoulder width (P = .001, r2 = 0.509), and soft tissue at C1 measured from posterior arch on CT (P = .004, r2 = 0.444). The angle measured from a plumb line through the CT scout radiograph and a line connecting the inion to the spinous process of C2 also correlated to AP diameter (P = .046, r2 = 0.309). The width of decompression also correlated to the cranial-caudal height (P < .001, r2 = 0.522). A linear regression model demonstrated that cranial-caudal height was predicted (F (16,22) = 2.654, P = .017, r2 = 0.659) by age, maximum SOC width, and BMI (ß = -0.421, P = .031, 95% CI = (-1.067, -0.058)). CONCLUSION We demonstrate that a number of anatomic factors affect the ability to achieve optimal SOC size. While these factors are not modifiable, awareness of these factors may help guide positioning and operative planning to achieve maximum cerebellar decompression and help improve patient functional outcomes after emergent suboccipital decompression.