[Intracranial arachnoidal cysts--localization, gender and sidedness].

The aim of the present study was to investigate whether data on location and distribution of intracranial cysts in a large patient population may explain why and how such cysts are formed. We investigated 123 patients with 129 intracranial cysts, consecutively admitted to the Department of Neurosurgery in Bergen 1988-97. Data were analyzed with regard to intracranial location and gender distribution. Cysts were much more commonly located in the temporal fossae than one would expect if the distribution were random; 68.1% of patients had temporal cysts. We suggest a theory that may explain how mal-development of the leptomeninges may contribute to the formation of cysts, and why such cysts are more common in the temporal fossae. Temporal cysts were significantly more frequent in males than in females (3.9:1), while cysts of other locations did not show preponderance for a specific gender. New in this study is the interesting connection between gender distribution and sidedness: the significant predominance of left-sided temporal cysts was found only in males. In patients with a unilateral temporal cyst, the left/right ratio was 2.0:1 (males 44 left and 20 right, females eight left and six right). We discuss whether the preponderance of left-sided temporal cysts in males can be explained by a gender specific developmental failure, as previously suggested for dyslexia.