Researchers at the Universite Catholique de Louvain, Brussels, Belgium, and Universite de Sherbrooke, Quebec, Canada studied 2 patients presenting with arachnoid cysts associated with cognitive impairment., particularly language impairment. Patient 1, a 6-year-old, right-handed boy had a large head, articulation and phonology anomalies, and a normal intelligence. MRI revealed a left temporal lobe arachnoid cyst, and PET scan showed decreased metabolism in the left superior temporal gyrus and thalamus. A 24 hour-EEG was normal. A cysto-peritoneal shunt was placed at age 6 years. Postoperative MRI, 2 months after surgery, showed disappearance of the cyst and full reexpansion of the temporal lobe parenchyma. PET at 21 months postoperatively revealed a normal symmetric temporal lobe signal. The boy's phonology improved and was normal at 12 months postoperatively. Neuropsychological assessment repeated from 6 to 70 months postoperatively revealed language and attention span improvements, and an increase in full-scale IQ from 93 to 112, with no learning disabilities evident.
Patient 2, a 7-year-old, right-handed boy was admitted for chronic headaches of increasing intensity, associated with occasional vomiting. Neurologic exam was normal. Neuropsychological evaluation showed attention deficits, deficits in verbal comprehension, speech and syntactic, and in word definitions. Full scale IQ was normal. MRI at age 8 years showed a large arachnoid cyst at the base of the left sylvian fissure, causing a mass effect on the temporal lobe. 24 hour-EEG showed rare bursts of generalized spike and wave activity. A cysto-peritoneal shunt relieved the headaches and reduced the cyst volume. Postoperative EEG was similar to the original. Neuropsychological re-examination at 6 months showed improved verbal comprehension and attention. IQ remained the same, with verbal IQ of 98 and performance IQ of 105. 
COMMENT. The authors consider the following as evidence of cause and effect between the surgery and cognitive improvement: 1) close temporal relationships; 2) PET increased metabolic activity in the affected temporal lobe after surgery; and 3) a correlation between the language impairment profiles and the location of the mass effect. A syndrome of temporal lobe arachnoid cyst and ADHD is further evidence supporting an association between these cysts and attention and behavioral disorders. Treatment is usually conservative, relying on medications, academic and behavioral modifications.