Spinal perineurial and meningeal cysts.

Perineurial cysts may be responsible for clinical symptoms and a cure effected by their removal. They do not fill on initial myelography but may fill with Pantopaque some time, days or weeks, after Pantopaque has been instilled into the subarachnoid space. Perineurial cysts arise at the site of the posterior root ganglion. The cyst wall is composed of neural tissue. When initial myelography fails to reveal an adequate cause for the patient's symptoms and signs referable to the caudal nerve roots, then about a millilitre of Pantopaque should be left in the canal for delayed myelography which may later reveal a sacral perineurial cyst or, occasionally, a meningeal cyst. Meningeal diverticula occur proximal to the posterior root ganglia and usually fill on initial myelography. They are in free communication with the subarachnoid space and are rarely in my experience responsible for clinical symptoms. Meningeal diverticula and meningeal cysts appear to represent a continuum. Pantopaque left in the subarachnoid space may convert a meningeal diverticulum into an expanding symptomatic meningeal cyst, as in the case described. Many cases described as perineurial cysts represent abnormally long arachnoidal prolongations over nerve roots or meningeal diverticula. In general, neither of the latter is of pathological significance. Perineurial, like meningeal cysts and diverticula, may be asymptomatic. They should be operated upon only if they produce progressive or disabling symptoms or signs clearly attributable to them. When myelography must be done, and this should be done only as a preliminary to a probable necessary operation, then patient effort should be made to remove the Pantopaque.