ABSTRACT
Arachnoid or leptomeningeal cysts (ACs) represent intraarachnoid cavities containing a fluid similar to cerebrospinal fluid (CSF) that do not communicate with the ventricular system or the subarachnoid space. ACs have been the subject of some confusion concerning nosology as well as pathogenesis. Strictly speaking, AC should be regarded as a developmental abnormality of the arachnoid (Rengachary and Watanabe, 1981; Wester, 1999) and differentiated from focal leptomeningeal loculations that are secondary to trauma, neurosurgery, bleeding, or infection (Zülch, 1986; Go, 1993).
