EP05.71: First trimester detection of open spina bifida by assessing fetal cranial markers

Diagnosis of open spina bifida (OSB)is typically achieved during mid-pregnancy either by direct visualisation of spinal lesions or through identification of indirect signs such as the “banana sign” and “lemon sign”. Directly observing spinal defects during early pregnancy is challenging, but due to cerebrospinal fluid leakage and intracranial negative pressure, effective screening for OSB can be achieved by monitoring changes in cranial signs. This case describes the detection of fetal OSB during routine first trimester ultrasound examination. The patient was a 29-year-old primigravida with no significant medical or obstetric history. In the midsagittal section of the fetal brain, the brainstem (BS) showed a downward displacement and widening, with a decrease in the distance of the brainstem to the occipital bone (BSOB). The ratio of the BS to the distance of the BSOB was increased (>1. The posterior brain region showed two hypoechoic areas instead of the normal three. Additionally, the junction of the thalamus with the midbrain is below the maxilla-occipital line, which is a valuable proposed ultrasonic marker for early diagnosis of OSB. The axial transventricular plane of the head showed that the choroid plexus fills almost completely the lateral ventricles, giving the appearance of a “dry brain”. However, the patient chose to continue the pregnancy. At the 22-week examination, significant abnormalities were detected in the fetal cranial structure, characterised by the banana sign. Simultaneously, we observed evident spinal defects. The patient eventually underwent induction of labour and the fetal autopsy revealed the presence of OSB. Screening for OSB during the first trimester of pregnancy is crucial, and attention should be paid to changes in cranial structures when spinal defects are not obvious. It allows for appropriate counselling and management by a multidisciplinary team to improve the quality of the birth population.