Introduction: Arachnoid cysts located in the middle cranial fossa still poses a clinical challenge and requires a staged approach. Accepted procedures include modalities differing in mechanism of action, i.e. communication of the arachnoid cyst with arachnoid cisterns by endoscopy or craniotomy (internal decompression) and placement of a shunt (external decompression). Therefore, arachnoid cysts may in fact represent a group of diseases with different underlying pathology. Material and methods: Between January 1980 and December 2017, a total of 276 patients were operated on for an arachnoid cyst of lateral fissure. Mean age was 6.5 years and mean follow-up time was 9.7 years. A retrospective analysis of medical records was performed. Statistical analysis was performed using the Chi-squared test with Yates’ correction. Results: A single surgical procedure was performed in 89% of patients (simple arachnoid cysts, SAC), whereas 2–4 procedures were needed in 11% of cases (complex arachnoid cysts, CAC). In the CAC group, internal and external decompression was effective in 20% and 80% of the cases, respectively. In the SAC group, the proportions were nearly exactly opposite (71.9% and 19.9%, respectively) (p < 0.001). A low-pressure cystoperitoneal shunt proved effective only in 4/30 patients (13%), the remaining patients required a switch to medium- or high-pressure shunt. Conclusions: 1) A small proportion of children with an arachnoid cyst have a coexisting cerebrospinal fluid absorption deficit. 2) In these cases, effective treatment consisted in placement of a medium- or high pressure shunt; low-pressure shunts produced symptomatic overdrainage. 3) Risk factors for this subgroup of patients are: younger age, epilepsy, ventriculomegaly and cyst mass effect at presentation.