Fifth International Hydrocephalus Workshop, Crete, Greece, May 20-23, 2010: themes and highlights.

The purpose of the Fifth International Hydrocephalus Workshop was to allow clinicians and basic science researchers to educate each other in the advances that have been and are being made in the understanding and treatment of hydrocephalus and related disorders. This vision of the meeting was the work of Dr. Anthony Marmarou, who died a few months before the meeting was held. The presentations on all aspects of the study of hydrocephalus can be roughly grouped into seven basic themes. These themes are a summary of the important lifelong work of Professor Marmarou himself, including mathematical modeling, clinical selection of patients for the treatment of normal pressure hydrocephalus, and the development of international guidelines for the management of this condition. Other themes included the gathering of data, and in particular, randomized controlled trials; the use of magnetic resonance imaging for basic research in hydrocephalus, basic science and in particular the role of aquaporins; reports on clinical studies; and the late outcomes for patients treated in infancy. Finally, a report on the development of a consensus on the definition and classification of hydrocephalus based on the point of obstruction to flow of cerebrospinal fluid was presented.

Overview of the CSF dual outflow system.

It was firmly established in the mid-twentieth century that the arachnoid villi represented an open pathway between the subarachnoid space and the dural venous sinuses. Intracellular and extracellular pathways within the villous structure provided the conduit for cerebrospinal fluid (CSF) and particulate matter. The importance of the lymphatic system was established by the demonstration of CSF tracers entering the nasal lymphatic system via the perineural subarachnoid space enveloping the olfactory nerve rootlets. It appears that because of the late development of the arachnoid villus (AV) system, the lymphatic outflow system is the more dominant one in the young animal, but in the mature animal the importance of both systems appears equal. In general, the lymphatic system in lower animals appears dominant, but in the case of primates, this may not be the case. The global outflow system has a definite opening pressure of ca. 50-70 mm of water, and the balance between production of CSF and absorption occurs at a resting pressure of ca. 115 mm water. The bicompartmental CSF outflow curves obtained from hydrocephalic patients support the presence of a dual outflow system utilized in normal CSF drainage.

The function and structure of the cerebrospinal fluid outflow system.

This review traces the development of our understanding of the anatomy and physiological properties of the two systems responsible for the drainage of cerebrospinal fluid (CSF) into the systemic circulation. The roles of the cranial and spinal arachnoid villi (AV) and the lymphatic outflow systems are evaluated as to the dominance of one over the other in various species and degree of animal maturation. The functional capabilities of the total CSF drainage system are presented, with evidence that the duality of the system is supported by the changes in fluid outflow dynamics in human and sub-human primates in hydrocephalus. The review also reconciles the relative importance and alterations of each of the outflow systems in a variety of clinical pathological conditions.