Hello, I am Ralph Albertani and this is a presentation on the historic evolution of intracranial pressure, two centuries of challenges. Monitoring intracranial pressure, or ICP for short, is a strategy to improve patient care and has become essential for neurosurgeons in the latest years. It is a result of 200 years of research conducted by anatomists and physiologists that really define what neurophysiology is today. This historical note revisits the history of the iconic Monroe-Kelley Doctrine, as well as other important contributions through classic manuscripts and articles. Articles and books were selected for this presentation using the scriptures Intracranial Pressure, Scriabin's Final Fluid Pulse, Monitoring, Monroe-Kelley Doctrine, and ICP waveform electronic databases, PubMed, LILACS, Science Academic Base. Monroe was a professor of anatomy and surgery at the University of Edinburgh. He investigated the structure of the nervous system and carried out studies on comparative anatomy. His most important contribution was a manuscript published in 1783 named Observations on the Structure and Functions of the Nervous System with Illustrated Tables. His conclusions were that brain tissue volume is mostly static, blood volume inside the skull does not vary significantly regardless of individual health conditions, and that any new added volume should result in the depletion of an equal volume, not a compartment. Kelley was a Monroe student at the University of Edinburgh. The autopsy of two men found that after a storm was the source of motivation for his studies. This physiologist carried out experiments with animals in which he studied the intracranial venous dynamics. His main objective was to understand cerebral circulation and how it's regulated. His conclusions were that the skull is a firm and inflexible structure in adults, the skull isolates its interior, namely the brain, from external mechanical pressure, the blood volume inside the skull hardly varies, and school depressions such as depression fracture will result in less blood flow to the brain. Albert Crombie was responsible mostly for spreading the Monroe-Kelley Doctrine among the medical community. In his book, The Pathological and Practical Researches of the Disease of the Brain and Spinal Cord, published in 1828, he attributed the doctrine of intracranial dynamics to Monroe-Kelley. He studied to reinforce the role of depressions of the skull in reducing blood flow and brought about the possibility of these being caused by the compression being exerted on brain tissue. This is a short timeline showing how CSF was seen through time. It was explored and reported by Egyptians back in 2000-2050 BC, and Galen had this hypothesis that the carotid plexus could be the producers of CSF. Later in the Middle Ages, ancient anatomists claimed that CSF would only exist after death and for a while, CSF was forgotten. In the Renaissance, several anatomists investigated the circulation of CSF, and in 1784, Domenico Contugno described CSF in different compartments. CSF was not mentioned barely at all by the group in Edinburgh, composed mainly of Monroe-Kelley and Albert Crombie. Only in 1842 did Magandí define CSF as a physiological fluid inside the skull. George Burroughs, in 1846, reformulated the Monroe-Kelley doctrine. He contested several points raised by his predecessors, such as the idea of the skull being a perfect skew of fear and the notion that blood volume does not vary at all, since he did find differences in different positions when he was trying to reproduce some of the studies carried out by Monroe-Kelley and Albert Crombie. He also attributed a significant role in the regulation of intracranial pressure to CSF, following the studies of Magandí. Other contributions of Zadok Northworthy, for example, from Henry de Ritt, that showed that increased pressure could cause blood volume compression, reducing cerebral blood flow, and also demonstrated that CSF absorption, reverted by ligament extensibility and even sinus collapse, would alleviate the increase in pressure in the early stages of intracranial hypertension. Ernst von Bergman demonstrated that CSF drainage into the elastic spinal canal is a mean of controlling this increased pressure. Theodor Koscher, in turn, established that in the first stages of ICP elevation there would be a compensation that could be a compensation through the drainage of CSF, compression of veins and capillaries, and displacement of brain tissue to the foramen magnum, which is what we know today as herniation. Harvey Cushing, the father of modern neurosurgery, demonstrated the clinical and physiological importance of the doctrine. He consolidated Berber's discovery with other discoveries from the past. Lewis Weed postulated that brain volume variation during life and that the doctrine of Monroe-Kelley could be applied in almost any situation. There has also been several disputes through the doctrine. For example, in 2012, Sergio Mascarenha and his collaborators questioned the supposed inaccessibility of the skull. Mascarenha and his colleagues demonstrated that even after closure of the fontanels, there were small volumetric changes in the skull due to volume changes, by which they meant that with volume changes in the brain, there is also small deformations of the skull, and this relates closely to the increase in intricate pressure. So there is a relation to these small deformations of the skull to increase intricate pressure. However, his group did not consider that such fact may suggest that the millimetric expansion of the skull may also be a compensatory element for the pressure rise inside the skull. We conclude that the Monroe-Kelley doctrine and its adaptations make up for a very important concept in neurosurgery, being the result of a myriad of studies carried out for over 200 years. Several physiologists and anatomists have worked on understanding the ancient cranial dynamics. Unfortunately though, many of these were forgotten as time passed and a doctrine was established. The process of consolidation of the doctrine enabled the understanding of several very important phenomena that are of great interest in neurosurgery. Abercrombie and Cushing stood out as great spreaders of the doctrine. These are our references. Thank you very much for your time today.

intracranial pressure monitoring

neurosurgery

evolution

anatomists

physiologists