In Reply.—
The case report by Alker et al (Archives 36:376-379, 1979) of a symptomatic space-occupying cyst in the region of the cisterna magna leaves several unanswered questions and leads to some speculation.1. Why was a computerized tomography study, including sagittal reconstruction, not performed? My colleagues and I had shown1 that sagittal reconstruction would differentiate a cyst of the cisterna magna from a Dandy-Walker cyst or variant. An air study would be unnecessary.2. Did this patient have a history of delay in acquisition of motor milestones, or macrocephaly?3. The authors clearly defined the asymmetry of occipital bone thinning, the neurological signs and symptoms, and the unilateral pressure effect on the right inferior aspect of the cerebellum at the time of operation. They demonstrated a unilateral posterior fossa cyst that filled with isotope injected into the lumbar thecal space.My colleagues and I believe that there are three types of