Q: What is the relationship between center line shifting and an internal bleeding? A: The phenomenon of "mid-line shift" as seen on a CT scan of the brain demonstrates shifting of the brain from one side to the other as a result of some sort of increased pressure. THe increased pressure can be due to any number of things such as a tumor, a hemorrhage (bleeding), or brain edema (swelling). Any bleeding on one side of the brain will always push the brain to the opposite side, thus the mid-line shift will be to the opposite side. For example a hemorrahge on the right side of the brain will push the brain to the left and the mid-line will shift from right to left. Q: Do areas of bleeding always appear darker on CT scans? A: No. Areas of bleeding are usually brighter on CT scan or "high density" as the radiologists would say. Once blood begins to break down into its metabolites it begins to become progressively darker. Q: What are the four different kinds of bleeding and how do we distinguish them visually. A: The four different kinds of bleeding are 1. Subarachnoid bleeding: This is bleeding in the subarachnoid spaces where the blood vessels course. This bleeding is usually in the basal cisterns and the interhemispheric fissure or sylvian fissure. It is not in the brain matter itself. You would have to see the CT scans of characteristic subarachnoid hemorrhages to distinguish from other types of bleeding. 2. Extra-axial bleeding which is usually subdural or epidural bleeding. THis is blood that is on the surface of the brain and not in the substance of the brain. This has a characteristic appearance as bright color on the surface of the brain. A subdural blood clot would be biconcave or crescentic in appearance. An epidural blood clot is characteristically biconvex or lenticular in appearance. 3. Intraaxial bleeding is a hemorrhage in the substance of the brain and it has no characteristic appearance except that it is in the brain matter and not on the surface of the brain. 4. Intraventricular bleeing is blood within the ventricles or fluid filled spaces of the brain. This is a bright color within the dark colored fluid chambers of the ventricles. Q: Are the visual cues such as shape, intensity, size , position/orientation of certain regions on the CT's sufficient for determining whether the patient has a tumor or a blood clot. What other tests are required? A: Yes usually the size, location , and density of a lesion can help distinguish between a tumor or a blood clot. Usually one would perform a CT scan with and without intravenous contrast agent. A tumor will usually, but not always, become brighter with the contrast agent whereas a blood clot will usually be bright on both contrast enhanced and non-contrast CT scans. Also a tumor tends to have a characteristic shape. Many times to distinguish between tumor or blood clot one would also obtain a MRI(magnetic resonance image) of the brain. Q: How does one tell a tumor from a bleeding? A: This is not a simple question to answer but there are some simple things to follow. First we look at the intensity of the lesion. An acute hemorrhage is usually homogeneously bright and will not change with the addition of intravenous contrast material. A tumor is usually not bright on a non-contrast CT scan but it will usually, though not always , become homogeneously or heterogeneously brighter with the addition of an intravenous contrast agent. Secondly, we look at the shape of a lesion. Tumors can be well circumscribed or diffuse. Hemorrhages are usually well defined and are usually either on the surface of the brain or deep withing the brain. Tumors can also be deep within the brain. To further complicate matters sometimes tumors can bleed themselves and appear as brain hemorrhages. Often times the distinction between a tumor and a hemorrhage is made with comparison of contrast enhanced and non-contrast CT Scans, MRI, and clinical history. Hemorrhages present with more sudden onset of symptoms such as headache or weakness or speech difficulties whereas a tumor is slow growing and symptoms may be the same but are progressive. Q:Do axial CT scans always appear to have bilateral symmetry? A: Yes. Axial CT scans are usually symmetrical. Asymmetry usually means some sort of abnormality is present but it can also be an artifact sometimes of the position of the patient's head in the CT scan machine. The asymmetry of poor patient positioning is seen with comparision of the bone anatomy. For instance if the petrous temporal bone is seen on one side but not the other it usually means the head is improperly positioned in the machine. In the absence of bone asymmetry, any other asymmetry would be viewed as suspicious for some sort of abnormality. Q: What are the things a physician first looks for in a set of Ct scan to decide whether there is an abnormality? A: First a physician would look to see if the CT is contrast enhanced or a non-contrast CT scan. Secondly we look at symmetry in bone anatomy and brain anatomy. Thirdly we look to the size of the ventricles. Fourth we look to the size of the basal cisterns. Then we look to the density of the brain to see if there are any bleeds or infarcts (darker on CT scan). Q: How does one tell if someone is normal or abnormal from his CT scans? A: This is another difficult question to answer in just a few sentences. Essentially though we look for asymmetry, abnormal color (brightness or darkness), bleeds on the surface of the brain, fractures of the bone, swelling of the soft tissue external to the skull. As I said above asymmetry would make one suspicious for some sort of abnormality, abnormal color would make one suspicious for a hemorrhage or a tumor or a stroke. Q: Do the CT scans from different patients look radically different. A: No. In general CT scans from patients of similar age are very similar if they are without any abnormailities. There is more variation in the appearance of the CT scans at the two extremes of age-- very young and very old.