The author describes the anatomical basis, the physical mechanisms, and clinical presentations of the spectrum of herniations of the brain. Included in the discussion of management of brain herniation is an update on the medical and surgical interventions utilized in the management of cerebral herniation.
• The Monroe Kellie hypothesis considers the craniospinal axis to be a closed system whereby in the setting of an increasing intracranial mass or diffuse edema intracranial pressure (ICP) the craniospinal axis will remain constant by a reduction in the volume of blood and or cerebrospinal fluid (CSF) until the compensatory ability is exhausted and ICP begins to rise.
• Transtentorial herniation is associated with the clinical triad of progressive deterioration of consciousness, ipsilateral pupillary dilatation, and hemiparesis of the contralateral side due to compression of the cerebral peduncle.
• Elevated ICP must be treated urgently with medical and surgical interventions to avoid brain herniation, decreased cerebral blood flow, and the resultant regional or global ischemia.
Historical note and terminology
During the 17th century, the human body began to be viewed as a system of subunits and independent compartments. This eventually led to the first human anatomical descriptions that mapped the body into different organs and tissues. As a result of this "subunit" or "compartment" theory, the Latin term herniation was employed to describe the protrusion of a portion of an organ or tissue through an abnormal passage. Within the skull, the brain is compartmentalized by rigid folds of the dura. The falx cerebri separates the 2 cerebral hemispheres. The tentorium cerebelli separates the occipital lobes from the cerebellum and brainstem. The falx cerebri partially separates the cerebellar hemispheres, and the sellar diaphragm covers the pituitary gland with a small opening to allow passage of hypophyseal veins and the infundibulum. Finally, the foramen magnum (Latin for “great hole”) is the boney opening at the base of the skull through which the spinal cord exits the cranial vault.
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