The brain has several features that distinguish it from other organ systems. The most important of these differences is that the brain is contained within the skull, a rigid and inelastic container. Because of this, only small increases in volume within the intracranial compartment can be tolerated before pressure within the compartment rises dramatically, causing neurological sequelae. This concept is known as the Monro-Kellie doctrine, which states that the total intracranial volume is fixed by the inelastic volume of the skull. This volume is divided into three compartments: the brain parenchyma, the blood volume, and the cerebrospinal fluid (CSF). When a significant head injury occurs, cerebral edema often develops, which increases swelling in the brain. Because the space inside the skull is fixed, the pressure within this compartment rises unless some action occurs to decrease in the volume of one of the other intracranial components.
In pediatric head trauma, the child’s brain presents a different developmental substrate for injury. It has greater water content than the adult’s, and is relatively resistant to damage from hypoxia. However, coma may still result from brainstem injury, or bilateral hemispheric damage.
The diagnosis of an unstable spinal injury and its subsequent management can be difficult, and a missed spine injury can have devastating long-term consequences. Therefore, spinal column injury must be presumed until it is excluded. The main concerns are which patients can be cleared by clinical exam alone, which imaging studies are necessary, and when should additional imaging be used. An assessment for ligamentous injury in the absence of a fracture is also important, especially in unconscious patients who are unable to complain of neck pain or tenderness.
Imaging studies have become of increasing importance in the evaluation and treatment of head and spinal trauma in the past 20 years, and recent advances have made CT and MRI more accurate and quicker for the assessment of traumatic injury. CT remains the investigation of choice even following the advent of MRI, due both to the ease of monitoring injured patients and the better demonstration of fresh bleeding and bony injury. MRI is the more sensitive of the imaging studies, having better resolution and greater sensitivity than a CT scan. However, it can’t be used if the patient has IV lines and ventilation equipment or pacemakers, because of its magnetic field; and the confined space of the MRI make it difficult to use in emergent situations. Yet, as valuable as these diagnostic tools have been in guiding intervention in acute management of the severely injured brain, normal scans do not rule out even life threatening brain trauma.