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© 2009 by the American Institute of Ultrasound in Medicine
J Ultrasound Med 28:999-1006 • 0278-4297

Supratentorial Abnormalities in the Chiari II Malformation, III

The Interhemispheric Cyst

Suzanne K. Wong, MD, A. James Barkovich, MD, Andrew L. Callen and Roy A. Filly, MD

Department of Radiology, University of California, San Francisco, California USA.

Address correspondence to Roy A. Filly, MD, Department of Radiology, University of California, 505 Parnassus Ave, L374, San Francisco, CA 94143-0628 USA., E-mail: roy.filly{at}radiology.ucsf.edu

Objective. Our clinical observations noted an interhemispheric "cyst," a protrusion of the posterior superior third ventricle, in fetuses with myelomeningocele (MMC). The study analyzed the frequency of this observation and features that influence its visualization. Methods. We searched for cases of fetal MMC sonographically detected between 1999 and 2007. Intracranial findings were retrospectively reviewed with attention to the interhemispheric cistern. Additionally, we reviewed 25 fetuses without a central nervous system anomaly and 10 fetuses with ventriculomegaly but no MMC. Results. Among 89 fetuses identified, the mean gestational age was 22 weeks 4 days. Thirty-eight (43%) had an interhemispheric cyst. The frequency was similar on sonograms judged to be well visualized compared with studies judged to be suboptimally visualized. The degree of ventriculomegaly, timing of diagnosis, and severity of the Chiari II malformation did not appear to influence the frequency of the finding. Among fetuses without a central nervous system anomaly, no interhemispheric cysts were detected; a cyst was detected in 1 of 10 fetuses with ventriculomegaly. Interhemispheric cysts were more likely to be detected in fetuses with the Chiari II malformation than fetuses with ventriculomegaly but without the Chiari II malformation (P = .04). Conclusions. Interhemispheric cysts are a common supratentorial feature of the Chiari II malformation. Their presence appears to be unrelated to other features of the Chiari II malformation. Although interhemispheric cysts are seen in other abnormal fetuses, their striking prevalence in the Chiari II malformation should lead to a thorough examination for MMC.

Key Words: abnormal third ventricle • Chiari II malformation • fetal sonography • interhemispheric cyst • myelomeningocele

Abbreviations: CSF, cerebrospinal fluid • MMC, myelomeningocele

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Copyright © 2009 by the American Institute of Ultrasound in Medicine.