Objectives: Intracranial arachnoid cysts are commonly characterized as congenital. Evidence to support a congenital origin is scant and documented evolution during infancy also calls into question the genesis of these lesions. To improve our understanding of the natural history and the clinical significance of arachnoid cysts on prenatal ultrasound, we conducted a study to describe the fate of these cysts after initial diagnosis.
Methods: We conducted a retrospective descriptive review of all prenatal ultrasounds with reported intracranial arachnoid cysts at a tertiary care center from 2010 to 2016 and cohort study comparing patients with additional ultrasound abnormalities to those with an isolated finding of arachnoid cyst. Data collected included gestational age at cyst diagnosis, cyst evolution on follow-up imaging, cyst size and cyst location, postnatal imaging and neurosurgical consultation and intervention. Statistical analysis including Chi-square and Fisher's exact tests and univariate logistic regressions were performed using Stata v. 13 (StataCorp 2013. Stata Statistical Software: Release 13. College Station, TX: StataCorp LP). Confidence intervals were reported at 95% and a p-value < .05 was considered significant.
Results: A total of 33,621 anatomical ultrasound scans were performed from 2010 to 2016. Seventy patients (0.2%) had prenatal findings of arachnoid cyst, of which the mean gestational age was 21.46 weeks. Ventriculomegaly was observed in one patient (1.4%) at the time of diagnosis and other abnormalities were found in twelve patients (17%). Complete sonographic follow-up prior to delivery was obtained in 53 (75.7%) patients with 5(9.4%) progression, 5(9.4%) regression, and 43(81.1%) no longer visualized. Forty-three cysts (81.1%) were no longer visualized on follow-up imaging, all of which were interhemispheric in location. All of the cysts that progressed in size on prenatal ultrasounds were > 2 cm in size on initial diagnosis. Cyst fenestration was performed in two patients (2.9%) that had arachnoid cysts measuring at least 3 cm in each dimension on prenatal imaging, one at eight months and one at six months of age. Patients with and without additional sonographic abnormalities had similar rates of AMA (23.1% vs 26.3%, p = .56), nulliparity (61.5% vs 70.2%, p = .38), obesity (0.0% vs 12.3%, p = .221), major medical comorbidities (38.5% vs 33.3%, p = .48) and pregnancy achieved via Assisted Reproductive Technology (38.5% vs 24.6%, p = .25), respectively. Patients with additional sonographic abnormalities were significantly more likely to have prenatal Magnetic Resonance Imaging (OR: 8.28, CI: 1.84-40.4, p = .07), prenatal neurosurgery consultation (OR: 8.25, CI: 1.23-69.05, p = .04) and invasive diagnostic genetic testing (OR: 11.25, CI: 2.33-64.35, p = .003).
Conclusions: Arachnoid cysts are infrequently found on prenatal screening. Size greater than 2 cm on second trimester ultrasound and location outside of the interhemispheric fissure may indicate the need for further evaluation and eventual fenestration. Prenatally diagnosed arachnoid cysts are not typically associated with other anatomic or genetic abnormalities, although the presence of additional abnormalities usually leads to more intensive prenatal and postnatal investigations.
Keywords: Arachnoid cyst; fetal brain; intracranial cyst; neurosurgery.