Pathologic factors found in the surgical investigation of epilepsy

Abstract

1. 1. In a series of 272 patients with the so-called “idiopathic” type of epilepsy, certain definite lesions have almost invariably been found at operation, the more common types being shown photographically. 2. 2. In some 225 of these cases, corticodural fixations at the cerebral vertex in or near the cortical motor areas were localized roentgenologically by subdural air insufflation, in which cerebral postural displacement was artificially induced by allowing air to enter the subdural space. 3. 3. Arachnoidal defects or fistulas through which cerebrospinal fluid leaks into the subdural space have been found in practically every epileptic patient operated on since their characteristics have been recognized. These fistulas are probably the result of tears in the arachnoid which have failed to heal. They are usually located at the extreme vertex of the brain where the strain of gravity is greatest. 4. 4. During subdural air insufflation it is possible to demonstrate that cerebral postural stability is dependent on the maintenance of arachnoidodural approximation. This approximation is controlled by two factors: (1) fluid film adhesion between arachnoid and dura which maintains these structures in forceful apposition; (2) a negative subdural pressure which develops when fluid film adhesion is lost through an excess of subdural fluid. This subdural negative pressure maintains the brain in a certain degree of postural stability but tends to syphon cerebrospinal fluid into the subdural space through arachnoidal fistulas when such are present. 5. 5. The traction on the cortex which occurs in expansive lesions and corticodural fixations after craniocerebral trauma seems to be a factor responsible for the induction of convulsive phenomena in these two diverse pathologic conditions. During operation traction will serve to induce attacks. In the “idiopathic” type of epilepsy definite traction is exerted on corticodural attachments at the extreme vertex of the brain during postural displacement which occurs when there is an excess of subdural fluid. Subdural air insufflation, devised for the examination of the subdural space, serves in the localization of corticodural attachments; it shows the cerebral postural displacement which takes place when air or excessive fluid enters the subdural space; subdural fluid is determined by a definite fluid level which changes with position of the head. 6. 6. In this series the surgical correction of arachnoidal fistulas and the reduction of traction on corticodural attachments have so diminished convulsive attacks in the epileptic that one is justified in considering the lesions which are herein presented as definite causative factors in the chronic convulsive state.