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✓ Two cases of extradural arachnoid cysts or pouches of the thoracic spine are described. Surgical removal was effective in both instances. Theories of etiology are reviewed, particularly in regard to cerebrospinal fluid (CSF) dynamics. A simplified model of the development of these lesions is proposed, relating the law of Laplace to the cyst wall and neck. This theory, in conjunction with fluctuation of CSF pressure in response to venous influences, may explain the expansion of these loculations within the spinal canal.
McCrum et al. (Wed,) studied this question.