Association between cranial asymmetry severity and chronic subdural hematoma laterality

Objectives:To analyze the association between cranial asymmetry severity and chronic subdural hematoma (CSDH) laterality.Methods:We retrospectively assessed 120 patients with surgically treated unilateral CSDH from January 2009 to December 2018. Preoperative computed tomography images were used to determine occipital vault angles, bilateral cranium areas, and cranial index of symmetry (CIS) ratios.Results:The male sex (70%) was the predominant factor promoting CSDH pathogenesis. In the overall study population (mean age, 71.3 years; left-sided CSDH, 58/120 [48%] patients; right-sided CSDH due to right-sided flat cranium, 38 patients; left-sided CSDH due to right-sided flat cranium, 37 patients). Flat cranial asymmetry was nonsignificantly associated with CSDH laterality (p- value=.689). However, most CSDH patients (86.7% of 120 patients) presented dominant-sided nonoverlapping areas on the left side. Thirteen (81.3%) patients presenting right-dominant nonoverlapping areas had right-sided CSDH, and 55 (52.9%) patients had left-dominant nonoverlapping area had left-sided CSDH (p- value=0.01). The CIS ratio was significantly higher in patients with right-dominant nonoverlapping areas than in those with left-dominant nonoverlapping areas (97.2% vs 95.9%, p- value<0.0001).Conclusion:Left-sided hematoma predominance is not associated with a flat cranium and laterality of unilateral CSDH. Moreover, more asymmetric crania with lower CIS ratios may predict left-sided CSDHs, whereas the right-sided CSDHs may be more common in symmetric crania with higher CIS ratios. The CSDH laterality is potentially attributable to cranial asymmetry severity.

Chronic subdural hematoma (CSDH), a common neurosurgical entity, is considered a delayed manifestation of head trauma, occurring mostly in older men.1 Although CSDHs can occur in unilateral or bilateral intracranial spaces, left-sided predominance has been previously reported.2,3 Few studies have reported that cranial morphology and gravity contribute to the laterality of CSDH.4–6 Cranial asymmetry is more common among crania flattened toward the right side, influencing the left-sided predominance of CSDH.6 The cranial index of symmetry (CIS) with a semiautomated method has been introduced to objectively determine the severity of cranial deformations including plagiocephaly.7 A preliminary study reported that the objective nonradiographic method potentially serves as an unbiased measurement of cranial asymmetry.7 The flat side has been simply defined by a smaller angle through a simple method considering angles among 3 lines.4–6 However, the angles may be manually affected by the points of the intersection of the manually selected lines, thus obstructing cranial asymmetry assessment. Therefore, here, we aimed to clarify the association between the severity of cranial asymmetry and the laterality of CSDH by using an objective semiautomated method.