What provokes a disappearing arachnoid cyst? – Case study and literature review

Objective Intracranial Arachnoid cysts (AC) are stable cerebral spinal fluid (CSF)-filled sacs that can rarely undergo progressive shrinkage or disappearance throughout life. In this manuscript, we present a case of post-traumatic complete resolution of an AC, review the possible triggers of this phenomenon, and discuss the pathophysiological mechanisms behind them. Methods After presenting our case, we performed a literature review using the PubMed Database of all the reported cases of AC reduction or resolution (last updated in February 2021). Spontaneous cases were excluded. An analysis of the remaining cases (1985–2021) according to their inciting event, demographical, and clinical characteristics was then presented. Results 58 patients were identified, 33 of which spontaneously resolved. The remaining 25 were included in the survey in addition to the case we presented. The mean age was 20.2 years, average time to resolution was 25.3 months, with only two third of the cases showing complete disappearance of the AC. A central nervous system infection was the inciting cause of resolution in one infant (4%), a history of head trauma in 16 (62%) patients and an intracranial procedure in 9 (35%) patients. Discussion AC disappearance is a rare phenomenon that can occur spontaneously or after an inciting event. The cyst wall rupture and CSF flow perturbation theories seem to be the most applicable pathophysiological mechanisms in triggered AC resolution.