The occipitum-dens line: the purpose of a new ultrasonographic landmark in the evaluation of the relationship between the foetal posterior fossa structures and foramen magnum.

PURPOSE

The aims of this study were to describe a new ultrasonographic technique to assess the normal level of the cerebellum and the brainstem in the posterior fossa in normal foetuses and to compare in pathologic cases.

METHODS

We propose a new line cross between the dens cervical and the inferior portion of occipitum (occipitum-dens line-ODL). In a cross-sectional study, a single observer with experience in foetal neurosonography evaluated 54 foetuses (40 normal and 14 with open neural tube defect) between 20 and 28 weeks of gestation. The reference points for the ODL are principally the lower portion of the occipital bone (occipitum) and odontoid process of the second cervical vertebra (dens). The line was considered the level zero (near level of foramen magnum). Structures above it had a positive measurement and below it had a negative measurement.

RESULTS

Moreover, in most foetuses with open neural tube defect (93 %), the end portion of cerebellum was below the ODL associated with different degrees of ventriculomegaly.

CONCLUSION

The proposed innovation aims to bring to the ultrasound the most likely anatomical parameters of evaluation in normal foetuses and in foetuses with spinal dysraphism.