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EP01.01: Reliability of cavum septum pellucidum volume measurements during second trimester ultrasonography in structurally normal fetuses

Objectives: Cavum septum pellucidum (CSP) is an important intracranial structure that is necessarily visualised during routine second trimester sonography. A small or a large CSP may suggest abnormal cerebral development. Therefore, determination of CSP volumes can be useful. However, consistency of sonographic measurements for this relatively small structure is a concern. For this purpose, we sought to assess the reliability of CSP volume measurements with three-dimensional ultrasound between 19–24 weeks of gestational age in structurally normal fetuses. Methods: Three-dimensional Virtual Organ Computer-aided Analysis (VOCAL) software was used to calculate the CSP volume from transabdominal multiplanar datasets obtained during 99 consecutive normal fetal ultrasound examinations within a single unit. Agreement among 3 independent observers with different experience levels of ultrasonography (year 2 obstetrics and gynecology resident, year 2 maternal-fetal medicine fellow, and maternal-fetal medicine specialist) was evaluated, using absolute agreement intraclass correlation coefficients (ICC) and 95% confidence intervals (CI). Results: Measurement of CSP volume was possible in all of the fetuses by all examiners. Interobserver agreement between fellow and specialist was relatively high (ICC, 0.78; 95% CI, 0.70–0.85), whereas limited ultrasound experience (resident) was associated with fair agreement with other observers (ICC for resident and specialist, 0.50; 95 CI%, 0.29–0.65 and ICC for resident and fellow, 0.57; 95% CI, 0.38–0.71). Conclusions: Three-dimensional ultrasound CSP calculations using VOCAL software between 19–24 weeks of gestational age seem feasible, but are reliable only when evaluated by an examiner with particular fetal sonography experience.