In 1923 Ayala1 suggested the rachidian quotient as a means of ready differential diagnosis of an expanding intracranial lesion and other causes of increased intracranial pressure. The amount of drop in pressure after removal of a given amount of spinal fluid apparently differs in cases of tumor of the brain and those of hydrocephalus or serous meningitis. Balduzzi2 confirmed the value of this index about a year later, and Claude and his co-workers3 in 1928 added a note on the clinical importance of the quotient. No other extensive studies have attempted to evaluate this relatively simple clinical procedure. Perusal of the neurologic literature of the last ten years shows the occasional use in differential diagnosis of this index by various clinicians.4 There has been no systematic attempt by English or American investigators to test the value of this clinical procedure. Pollock and Boshes,5 in a
SAVITSKY N, KESSLER MM. THE AYALA INDEX. Arch NeurPsych. 1938;39(5):988–1002. doi:10.1001/archneurpsyc.1938.02270050114006
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