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.

A lumbar spinal extradural ganglion cyst is reported, and the world literature on spinal ganglion cysts is reviewed. The clinical presentation, findings, etiology, and pathogenesis of these lesions are discussed.

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By the perfusion of arachnoid villi in excised simian dura mater, the passage through the villi of colloidal gold (.2–.3 µ diam), polystyrene microspheres of 1.17 µ and 1.8 µ, yeast (3–6 µ), goat erythrocytes (4 µ) and monkey erythrocytes (7.5 µ) was demonstrated. Polystyrene microspheres in the 6.4–12.8-µ range were excluded from passage. During the perfusion of the particles an impedance to flow most often developed and the particles were demonstrated by later microscopic examination to be enmeshed in the villi. Upon perfusion of mixtures of various sizes there was not found to be discrimination in passage based on size as long as the particles were beneath threshold size. It is concluded that these observations confirm the surmise, made earlier on anatomical evidence, that the villi provide open communication between the meninges and the venous system.