Arachnoid Cyst in the Posterior Fossa and Its Contested Association with Mania and Psychotic Symptoms in a Prepubertal Child: A Case Report.

Bipolar affective disorder presenting as a primary diagnosis in prepubescent children remains a contentious issue. Studies examining how common it is have yielded mixed, sometimes contradictory findings. One might argue that many of the rare cases described could actually be secondary to underlying neurological problems. In this report, we describe a 10-year-old girl with a posterior fossa arachnoid cyst who displayed a cluster of manic and psychotic symptoms. The clinical picture was marked by a sudden onset of irritability and hyperactivity, along with paranoid delusions. Of particular interest was a relapse after stopping medication. An initial EEG raised the possibility of epileptiform activity, but thorough follow-up testing failed to confirm this. Treatment with olanzapine and oxcarbazepine brought about some improvement, though not complete remission. Surgery was ultimately not pursued, as the cyst was deemed incidental. This case really discusses the difficulty in differentiating primary psychiatric illness from neuroimaging findings that may or may not be relevant. We propose that this might be a rare example of very early-onset mania, with the arachnoid cyst merely an incidental finding. It is worth noting that while there is some literature hinting at links between posterior fossa abnormalities and psychopathology, the evidence remains inconclusive. For a fuller picture, we include a one-year follow-up to shed light on the course of this complex presentation.