It is still an exceptional opportunity that makes possible the examination of cerebrospinal fluid obtained elsewhere than from the lumbar sac. While there are physicians who still look on lumbar puncture as an exceptional procedure, there are few who will not consider an examination of fluid at some other locus of the cerebrospinal system as extraordinary and unwarranted. Therefore our knowledge of fluid pathology in different parts of the ventricular-subarachnoid spaces advances slowly, and our conceptions of normalcy in these hidden regions becomes in a way a by-product of pathology. It should be emphasized here that in the case of an ambient fluid, postmortem study is of limited value and sometimes misleading.
Certain spaces in the ventricular-subarachnoid fluid system have been tapped sufficiently often to warrant an estimate of normal conditions at these loci, and to present in a number of pathologic states abnormal findings consistent enough to suggest their
AYER JB, SOLOMON HC. CEREBROSPINAL FLUID FROM DIFFERENT LOCI. Arch NeurPsych. 1925;14(3):303-314. doi:10.1001/archneurpsyc.1925.02200150016002