Surgery of arachnoid pouches.

An anecdotal presentation of some features of subarachnoid pouches stresses the variable clinical and morphological features. Hydrocephalus is commonly associated but is not always a cause nor a result of the pouches. The nature of the valvular action is unclear but most probably usually takes the form of plugs of nervous tissue, compression of perivascular spaces in the depths of sulci or else meningeal flaps forming slits in the CSF pathways. The nature of the filling force is almost certainly pulsatile and dependent upon venous impulses generated within the thoraco-abdominal cavities. Treatment may need to be directed against the pouch, or the hydrocephalus. Treatment of the valvular mechanism alone by dissection is frequently sufficient. Opening the pouch widely to the ventricular system may also be of value. Post-operative surveillance is necessary.