So on a CT scan, subdural hematomas follow the contour of the brain and form a crescent shape and cross suture lines.

所以在CT上，下血肿的轮廓和大脑轮廓一致，呈新月形，过颅缝。

Since the outer layer of the dura mater adheres tightly to the skull at sutures, epidural hematoma don't cross suture lines, and they push on the brain, forming a bi-convex shape.

由于脑外层与颅骨在颅缝处紧紧相，外出血不会过颅缝，且血肿会压迫大脑，形成双凸镜形。

Subdural hematomas cross suture lines and follow the contour of the brain forming a crescent shape, unlike epidural hematomas which don't cross suture lines and push on the brain and form a bi-convex shape.

下血肿可过颅缝，与大脑轮廓一致，呈新月形；相形之下，外血肿不过颅缝，而且压迫大脑呈双凸镜形。