@jteleia you are welcome. What I mean by axial is the raw CT images that are generated by rotating your body around its axis (90 degree) to the body. Simply put, it is the raw CT images, not the 3D rendered ones. 3D rendering can make organs touch each other (like vessel and bone) without them truly touching so it is less reliable than the actual raw CT slices. This is because the tissue size and the appearance of 3D images depends on the volume rendering intensity you choose (you can make them transparent by reducing the intensity or make them opaque by increasing it so this can introduce artifacts that may not exist in reality so any contact you observe should be confirmed with the raw CT slices).
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You can use this tutorial to teach you how to remove body parts such as the jaw as you asked if you intend to use the free 3D slicer software (Making Your Own 3D Images from CT Scan- 3D Slicer Tutorial - #4 by SnappleofDiscord)
Well I am not a doctor and certainly did not examine your CT to speculate what can cause it and frankly should be leaving it to doctors since it is their area of expertise. If the doctor thinks it is pressure that created the skull hole, then I think you should have asked him whether a compression/narrowing of the the right Jugular vein just below the skull by the Styloid process/C1 could have contributed the pressure build around the skull entry. That would have been significant indicator of why the blood is pooling around the skull entry. I, however, know that pressure (force applied on an area) can erode any material and the rate it erodes depends on the makeup of the material being eroded and the size and the duration of the pressure applied (this is from science perspective, not medical one).
Well again if Dr M said the blood was going backwards, you should have asked him what that means. When you said left side, I take it you mean the left internal jugular vein and if that is the case, then, does it mean because it is occluded/obstructed/compressed so that the blood has no choice but to flow backward (retrograde bloodflow is usually a sign of the vessel being occluded). I would ask all these questions. I hope I answered all your questions here.