Ultrasound and Magnetic Resonance Imaging of Agenesis of the Corpus Callosum in Fetuses: Frontal Horns and Cavum Septi Pellucidi Are Clues to Earlier Diagnosis.

OBJECTIVES: We hypothesized that: (1) fetal frontal horn (FH) morphology and their proximity to the cavum septi pellucidi (CSP) can assist in suspecting complete agenesis of the corpus callosum (cACC) and partial agenesis of the corpus callosum (pACC) earlier than known indirect ultrasound (US) findings; (2) FHs assist in differentiating a true CSP from a pseudocavum; and (3) magnetic resonance imaging (MRI) is useful in learning FH morphology and pseudocavum etiology. METHODS: Thirty-two patients with cACC and 9 with pACC were identified on an Institutional Review Board-approved retrospective review. Of the 41 cases, 40 had prenatal US, and 21 had prenatal MRI; 17 had follow-up neonatal US, and 14 had follow-up neonatal MRI. Variables evaluated retrospectively were the presence of a CSP or a pseudocavum, ventricle size and shape, and FH shape (comma, trident, parallel, golf club, enlarged, or fused). Displacement between the inferior edge of the FH and the midline or cavum/pseudocavum was measured. RESULTS: Fetal FHs had an abnormal shape in 77% ≤20 weeks' gestation, 86% ≤24 weeks, and 90% >24 weeks. Frontal horns were laterally displaced greater than 2 mm in 85% ≤20 weeks, 91% ≤24 weeks, and 95% >24 weeks. The CSP was absent in 100% of cACC cases and 78% of pACC cases, and a pseudocavum was present in 88% of cACC cases and 78% of pACC cases across gestation. Magnetic resonance imaging confirmed US pseudocavums to be focal interhemispheric fluid or an elevated/dilated third ventricle. CONCLUSIONS: Frontal horns assist in assessing ACC ≤24 weeks and throughout gestation. Pseudocavums, often simulating CSPs, are common in ACC. Frontal horn lateral displacement and abnormal morphology, recognized by MRI correlations, are helpful in differentiating a pseudocavum from a true CSP. A normal CSP should not be cleared on screening US unless normally shaped FHs are seen directly adjacent to it.

Fetal Ultrasound and Magnetic Resonance Imaging Findings in Suspected Septo-Optic Dysplasia: A Diagnostic Dilemma.

OBJECTIVES: To investigate prenatal imaging findings supporting a diagnosis of suspected septo-optic dysplasia (SOD) by fetal ultrasound (US), magnetic resonance imaging (MRI), or both. METHODS: A retrospective review identified 11 patients with SOD: 9 had a clinical diagnosis of SOD postnatally, and 2 were terminated on the basis of suspicious prenatal imaging. Prenatal and neonatal imaging of the cavum septi pellucidi (CSP), frontal horns (FHs), and lateral ventricles was evaluated. RESULTS: The appearance of the CSP varied on US and MRI. Complete ("fused") FHs or partial absence of the CSP was reported in 6 of 11 patients by fetal US and 7 of 8 patients by fetal MRI. The diagnosis of SOD was prospectively suspected prenatally in 6 of 11 and in an additional 5 of 11 cases retrospectively. Fetal MRI incorrectly initially reported normal morphologic abnormalities for 2 cases with partial absence of the CSP, whereas US accurately identified the morphologic abnormalities in 1 of these cases before MRI. Imaging features were first suggested at anatomic US (4 patients) and follow-up prenatal US (2 patients). Neonatal imaging was concordant in all 9 live births: 5 completely absent CSP, 3 partially absent CSP, and 1 completely present CSP. Clinical manifestations included optic nerve hypoplasia (9 of 9), panhypopituitarism (5 of 9), and neurodevelopmental delays. CONCLUSIONS: Primary imaging features of SOD are "continuous" FHs with complete or partial absence of the CSP. Septo-optic dysplasia can be suspected in utero and can appear isolated but has substantial associated central nervous system anomalies identified on fetal MRI or after birth. Partial absence of the CSP can be a prenatal sign of suspected SOD, although fetal MRI lacked the spatial resolution to identify it accurately in all cases.

Ultrasound Measurements of Frontal Horns and the Cavum Septi Pellucidi in Healthy Fetuses in the Second and Third Trimesters of Pregnancy.

OBJECTIVES: To assess the visualization rate and size of the frontal horns (FHs) and cavum septi pellucidi (CSP) in healthy fetuses throughout pregnancy. METHODS: After Institutional Review Board approval, 522 consecutive uncomplicated singleton pregnancies between 15 and 39 gestational weeks were enrolled in the study. Ultrasound measurements of the anterior horn width (AHW), center from the horn distance (CFHD), distance from the FHs to the CSP, and CSP width were retrospectively performed using axial transventricular or transcerebellar planes. Available maternal body mass indices were recorded. RESULTS: At least 1 FH was seen in 78% of the cases. The mean AHW decreased over the second trimester and plateaued in the third trimester. The CFHD plateaued in the second trimester and increased in the third trimester. Downside FHs were generally larger than upside FHs. More FHs were measured in transventricular (69%) than transcerebellar (31%) planes. Frontal horns were seen with high, low, and no confidence in 57%, 21%, and 22% of cases, respectively. No-confidence rates were 17% in the second trimester and 42% in the third trimester. The CSP was not visualized in 4% of cases; 15 of 19 cases of a nonvisualized CSP were scanned between 18 and 37 weeks. Mean body mass indices ± SDs were 27.6 ± 6.7 kg/m2 for the patients in cases of a visualized CSP and 32.4 ± 9.1 kg/m2 for the patients in cases of a nonvisualized CSP. CONCLUSIONS: Normative data for the fetal FH and CSP width were established. Frontal horns are more frequently seen on transventricular views and are difficult to confidently assess in the late third trimester. This study challenges previously reported data that the CSP is seen in 100% of cases from 18 to 37 weeks.