Prolonged ICP monitoring in Sylvian arachnoid cysts

The decision making process for patients with Sylvian fissure arachnoid cysts still represents a challenge for the neurosurgeon. A high percentage of patients are indeed asymptomatic, despite neuroimaging signs of apparently increased intracranial pressure (ICP). The present study was conducted to evaluate the usefulness of prolonged ICP recording in the preoperative work-up.

Eleven children (10 M/1 F) harboring temporal arachnoid cysts were investigated (mean age: 5.9 years). According to Galassi classification they were subdivided in three groups. Group I was made up of three patients with Type I cysts; Group II comprised six children with Type II cysts; Group III consisted of two children with Type III cysts. An extensible silicone microprocessor (Codman), developed for continuous ICP recording, was implanted intraparenchymally, adjacent to the major extension of the cyst. The collected information was cable unloaded to a PC and stored. All the patients underwent a minimum of 48 hours to a maximum of 72 hours of ICP continuous check. In resting conditions, 10 mm Hg was arbitrarily chosen as the upper normal limit of ICP, and the patients were classified according to the percentile distribution of their ICP daily and nightly pressure values.

ICP recordings were in the normal range in all the three children with Type I cysts (49-86%< 10 mm Hg during the entire recording), despite the fact that two of them were apparently symptomatic. Three of the six children with a Type II temporal cyst had elevated ICP values (69-99%> 10 mm Hg), even though they had an incidental (1 case) or prenatal (2 cases) diagnosis. The remaining three patients had normal ICP values for more than 70% of the recording time period. The two patients with type III temporal arachnoid cysts had almost constantly abnormal ICP values (95-99%> 10 mm Hg). Five patients were operated; in four of them the surgical indication was based on ICP recordings (two of the three children with a Type II cyst and increased ICP and the two patients with a Type III cyst). The last child, harboring a Type I cyst, was operated upon parents' request, as a preventive measure. At a mean follow-up of 9.3 months all the patients operated on are in excellent clinical condition; one of them (Type II cyst) initially undergoing a craniotomy and cystic membrane excision required a subduro-peritoneal shunt implant 3 months after surgery for a symptomatic subdural hygroma on the side of the cyst. Postoperative computed tomography showed signs of brain expansion in the two patients operated on for a Type III cyst, and in the patient operated on for a Type I cyst.

With the limit of the relatively small series presented here, prolonged ICP recording appeared to be an important preoperative tool to rule out the necessity of operating on children with Type I cysts. Furthermore, the study confirmed that an increase of the ICP is almost constantly present in children with Type III cysts. In cases of Type II lesions, the study results were less discriminating, though the ICP monitoring contributed in identifying those patients in whom surgery was indicated despite the absence of symptoms.