The symptoms occur in this order because the parasympathetic fibers surround the motor fibers of CN III and are hence compressed first. CN VI) and the superior oblique (innervated by trochlear nerve a.k.a. This palsy presents as deviation of the eye to a "down and out" position due to loss of innervation to all ocular motility muscles except for the lateral rectus (innervated by abducens nerve (a.k.a. Pupillary dilation often precedes the somatic motor effects of CN III compression called oculomotor nerve palsy or third nerve palsy. CN III), which may affect the parasympathetic input to the eye on the side of the affected nerve, causing the pupil of the affected eye to dilate and fail to constrict in response to light as it should. The uncus can squeeze the oculomotor nerve (a.k.a. Tissue may be stripped from the cerebral cortex in a process called decortication. The tentorium is a structure within the skull formed by the dura mater of the meninges. In uncal herniation, a common subtype of transtentorial herniation, the innermost part of the temporal lobe, the uncus, can be squeezed so much that it moves towards the tentorium and puts pressure on the brainstem, most notably the midbrain. ģ) Cingulate ( subfalcine or transfalcine)Ħ) Upward (upward cerebellar or upward transtentorial) Supratentorial refers to herniation of structures normally found above the tentorial notch, and infratentorial refers to structures normally found below it. There are two major classes of herniation: supratentorial and infratentorial. The tentorium is an extension of the dura mater that separates the cerebellum from the cerebrum. These symptoms are known as Cushing's Triad: hypertension (with widening pulse pressure), irregular respirations (commonly Cheyne-Stokes), bradycardia and in severe cases cardiac arrest. Cardiovascular and pulmonary symptoms may also be present as the brain loses function, but might also be associated with bleeding. Severe headaches and seizures as a result of increased intracranial pressure are not uncommon. Vomiting can also occur due to compression of the vomiting center in the medulla oblongata. One or both pupils may be dilated and fail to constrict in response to light. These patients have a lowered level of consciousness, with Glasgow Coma Scores of three to five. Therefore, extreme measures are taken in hospital settings to prevent the condition by reducing intracranial pressure, or decompressing (draining) a hematoma which is putting local pressure on a part of the brain.ĭecorticate posturing, with elbows, wrists and fingers flexed, and legs extended and rotated inwardīrain herniation frequently presents with abnormal posturing, a characteristic positioning of the limbs indicative of severe brain damage. īecause herniation puts extreme pressure on parts of the brain and thereby cuts off the blood supply to various parts of the brain, it is often fatal. In such cases local pressure is increased at the place where the herniation occurs, but this pressure is not transmitted to the rest of the brain, and therefore does not register as an increase in ICP. Herniation can also occur in the absence of high ICP when mass lesions such as hematomas occur at the borders of brain compartments. Herniation can be caused by a number of factors that cause a mass effect and increase intracranial pressure (ICP): these include traumatic brain injury, intracranial hemorrhage, or brain tumor. The brain can shift across such structures as the falx cerebri, the tentorium cerebelli, and even through the foramen magnum (the hole in the base of the skull through which the spinal cord connects with the brain). MRI showing injury due to brain herniationīrain herniation is a potentially deadly side effect of very high pressure within the skull that occurs when a part of the brain is squeezed across structures within the skull.
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