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.