Brainstem-vermis and brainstem-tentorium angles: 3D ultrasound study of the intra- and inter-observer agreement

Objective: The brainstem-vermis angle (BVA) and the brainstem-tentorium angle (BTA) have been proposed to quantify vermian and tentorial alterations associated to fetal posterior fossa malformations. Our objective is to evaluate the intra- and inter-observer agreement for the measurement of these angles during the prenatal ultrasound scan.

Methods: Fifteen 3 D sets from fetuses with posterior fossa pathology were processed by multiplanar navigation. Four experts in prenatal ultrasound measured the BVA and the BTA on a mid-sagittal view of the fetal brain, following the criteria described by Volpe. Observer 1 did also repeated measurements following both the criteria by Volpe and Ghi. The intraclass correlation coefficient (ICC) was used to test consistency and absolute agreement for intra- and inter-observer measurements. The concordance is poor when ICC <0.40 and excellent when ICC >0.75.

Results: Consistency ICC for measurements between the 4 observers was 0.74 (95% CI: 0.54-0.89) for the BVA and 0.55 (95% CI: 0.29-0.78) for the BTA. Absolute agreement ICC was 0.67 (BVA) and 0.45 (BTA). The intra-observer study showed a significantly greater angle with the criteria by Ghi (mean 52.1°, 95% CI: 49.5-54.8) than with the criteria by Volpe (mean 37.4°, 95% CI: 33.1-41.6).

Conclusions: A more precise methodology for the measurement of these angles should be described.