Banana Sign Research Articles

New ultrasonographic criteria for the prenatal diagnosis of Chiari type 2 malformation

During prenatal ultrasonography, characteristic malformations including the lemon sign, the banana sign, and obliteration of the cisterna magna are widely used for diagnosis of Chiari type 2 malformation (Arnold Chiari malformation). However, these signs are often obscured by 25 weeks' gestation. Here, we report an investigation of ultrasonographic markers of Chiari type 2 malformation for diagnosis after 24 weeks' gestation. Twenty-two cases of 24-37 weeks' gestation referred as fetal ventriculomegaly were analyzed prospectively. Fetuses were examined with ultrasonography by axial section of the head to detect conventional signs, and then by coronary section of the posterior horn of the lateral ventricle to detect two prospective new signs: bilateral downward-triangle shape (triangle sign) and quadrilateral angular shape (square sign). From the axial sections, three cases were diagnosed with holoprosencephaly, but the remaining 19 cases did not show the lemon sign. In the coronary sections, the eight cases that showed the triangle sign were associated with open spina bifida at the lower vertebral site. The four cases that displayed the square sign showed upper spinal lesions. Chiari type 2 malformation was suspected in these 12 cases. Four of the other seven cases were suspected to be agenesis of the corpus callosum, and the remaining three were normal. All ultrasonographic findings were consistent with the subsequent MRI and postpartum definitive diagnoses. At 24 weeks' gestation or later, Chiari type 2 malformation can be precisely and efficiently diagnosed by two new characteristics detected during ultrasonography: triangular shape and quadrilateral angular shape.

Plea for an anatomical approach to abnormalities of the posterior fossa in prenatal diagnosis

Plea for an anatomical approach to abnormalities of the posterior fossa in prenatal diagnosis

Integrating 2D and 3D Multiplanar Sonography in the Prenatal Diagnosis of Arnold-Chiari Type 2 Malformation

Arnold-Chiari type 2 malformation is a congenital deformity characterized by displacement of cerebellar tonsils, parts of the corpus callosum, and the medulla oblongata through the foramen magnum into the spinal canal. Sonographic diagnostic criteria are based on the “lemon sign” of the cephalic pole, enlargement of the lateral ventricle, and abnormalities of the posterior fossa consisting of an anomalous profile of the cerebellar hemispheres (“banana sign”) associated with a reduced or absent cisterna magna. Identification of a large, open neural tube defect is the other hallmark of the prenatal sonographic diagnosis. Multiplanar 3D enhances the definition and the exact extension of the spine defect and has the potential of calculating the amount of cerebellar hemispheres undergoing herniation through the foramen of Magendie and Lutchka, which is one of the main factors in predicting or modifying the postnatal neurosurgery strategy and the subsequent postnatal neurodevelopmental outcome.

Prenatal diagnosis of Chiari II malformation

Chiari II malformation is a complex brain abnormality affecting the brainstem, the cerebellum and the spine, usually associated with ventriculomegaly. The prenatal sonographic diagnosis of this anomaly is mainly based on evaluation of the posterior fossa. The sonographic findings range from ‘effacement of the cisterna magna’, to the so-called ‘banana sign’, to the ‘absent cerebellum’, according to the severity of the posterior fossa dysmorphism. Measurement of the angle defined by the clivus and the supraocciput is a further biometric criterion that is highly accurate in recognizing the disease.

Prenatal diagnosis of Chiari II malformation

Chiari II malformation is a complex brain abnormality affecting the brainstem, the cerebellum and the spine, usually associated with ventriculomegaly. The prenatal sonographic diagnosis of this anomaly is mainly based on evaluation of the posterior fossa. The sonographic findings range from ‘effacement of the cisterna magna’, to the so-called ‘banana sign’, to the ‘absent cerebellum’, according to the severity of the posterior fossa dysmorphism. Measurement of the angle defined by the clivus and the supraocciput is a further biometric criterion that is highly accurate in recognizing the disease.

False-positive diagnosis of spina bifida in a fetus with triploidy

Neural tube defects can be difficult to diagnose using ultrasound. Cranial markers, such as the lemon and banana signs, are useful sonographic findings that alert the ultrasonographer to examine the spine more carefully. The false-positive rate for the banana sign has been reported previously as zero. A patient with elevated maternal serum alpha-fetoprotein presented for a fetal ultrasound examination. Findings on the scan included a lemon sign, a banana sign, an effaced cisterna magna, and splayed lumbar vertebrae. After pregnancy termination, no spinal abnormality was detected on autopsy. X-rays of the fetal spine demonstrated narrowing in the thoracic spine. The karyotype of the fetus was 69,XXY. The sonographic cranial findings suggestive of a neural tube defect were misleading in this case.

Evaluation of the lemon and banana signs in one hundred thirty fetuses with open spina bifida

The incidence and diagnostic accuracy of the lemon and cerebellar ultrasonographic markers, as well as head size and ventriculomegaly, were evaluated in a study of 1561 patients at high risk for fetal neural tube defects. In the 130 fetuses with open spina bifida there was a relationship between gestational age and the presence of each of these markers. The lemon sign was present in 98% of fetuses at less than or equal to 24 weeks' gestation but in only 13% of those at greater than 24 weeks' gestation. Cerebellar abnormalities were present in 95% of fetuses irrespective of gestation; however, the cerebellar abnormality at less than or equal to 24 weeks' gestation was predominantly the banana sign (72%) whereas at gestations greater than 24 weeks it was cerebellar "absence" (81%). Both growth retardation and cerebral ventriculomegaly significantly worsened with gestation while the head circumference remained disproportionately small throughout gestation. On the basis of these data, a new approach is proposed for the investigation of patients at high risk for fetal open spina bifida.

ULTRASOUND SCREENING FOR SPINA BIFIDA: CRANIAL AND CEREBELLAR SIGNS

Ultrasound records were examined retrospectively in the cases of 70 fetuses with open spina bifida diagnosed by ultrasonography at 16-23 weeks' gestation. Biparietal diameter was below the 5th centile for gestation in 61% and head circumference measurements in 26%. The anterior horn of the lateral cerebral ventricle to hemisphere ratio was above the 95th centile in 77%, and ventriculomegaly of the posterior horn of the lateral venricle was observed in 86%. In the 54 fetuses for which pictures were taken at the level of the biparietal diameter a scalloping of the frontal bones (the lemon sign) was seen. In 12 of 21 fetuses for which a suboccipital bregmatic view of the cranium had been obtained, the cerebellar hemispheres were curved anteriorly with simultaneous obliteration of the cisterna magna (the banana sign); in a further 8 cases the cerebellum was not displayed. None of these changes was seen in 100 patients presenting consecutively for routine ultrasound examination in the second trimester.