Fetal thick corpus callosum: new insights from neuroimaging and neuropathology in two cases and literature review

Can cavum septum pellucidum width and length measurements also be reliable indicators of corpus callosum measurements in normal fetuses?

OBJECTIVE

To examine the association between cavum septum pellucidum (CSP) and corpus callosum (CC) length and width measurements in mid-trimester sonographic screening in normal fetuses.

METHODS

This prospective cohort study examined 152 pregnant women who underwent mid-trimester sonographic fetal anomaly screening. CSP and CC lengths and their anterior, middle, and posterior width measurements were examined sonographically. The association between length and width measurements of both structures, gestational week and CSP ratio (length/width) were evaluated.

RESULTS

The mean CSP length was 7.96 ± 1.09 mm, and the mean middle width was 3.43 ± 0.82 mm. The mean CC length was 20 ± 3.76 mm, and the mean middle width was 3.43 ± 0.82 mm. There was a positive correlation between CSP and CC lengths (r = 0.691, p < 0.001). There was also a significant correlation between CSP and CC anterior, middle and posterior widths (anterior (r = 0.366, p < 0.001), middle (r = 0.305, p < 0.001), and posterior (r = 0.233, p = 0.004)). All CSP and CC measurements were correlated with gestational age, biparietal diameter (BPD), and head circumference (HC) (p < 0.001, for all). The CSP ratio was not related to CC dimensions (p > 0.05, for all) and also decreased with the increase in BPD and HC dimensions (r = -0.186, p = 0.022, and r = -0.174, p = 0.032; respectively).

CONCLUSION

In normal fetuses, the length and width of the CC and CSP structures developed in relation to each other, as well as to the gestational week, BPD, and HC dimensions. In addition, while the CSP ratio was not found to be associated with CC dimensions, it decreased due to the increase in BPD and HC sizes.

Thick and Short Fetal Corpus Callosum on Ultrasound: Added Value of Fetal Magnetic Resonance Diffusion Tensor Imaging With Tractography

BACKGROUND

Thick fetal corpus callosum (CC) is a rare finding and its significance in isolation is not clear. In this retrospective study, we aim to gain insight into the microarchitecture of CC in a cohort of fetuses with thick and short CC (isolated or associated with mild extra-/intracranial abnormalities) as seen on ultrasound (US), by using prenatal magnetic resonance (MR) diffusion tensor imaging (DTI) with fiber tractography, thereby allowing better characterization for postnatal prognosis.

METHODS

Twelve fetuses met the inclusion criteria on US. The fetuses were further divided into group 1 (eight of twelve) with mild intra-/extracranial abnormalities or apparently isolated and group 2 (four of 12) with callosal lipoma (CL) on US. In all fetuses, both conventional MR imaging and DTI with tractography were done on 3T MRI.

RESULTS

DTI fiber tractography showed an aberrant midline longitudinal supracallosal bundle (ASB) in all eight fetuses in group 1. Three of four fetuses in group 2 showed normal callosal architecture, and one showed an abnormal sigmoid bundle suggestive of partial agenesis of CC.

CONCLUSIONS

We have for the first time demonstrated an ASB on MR DTI with tractography in eight of 12 fetuses with thick and short CC (isolated or mild associated intra-/extracranial abnormalities). Postnatally, ASB is reported to be associated with abnormal neurodevelopmental outcomes even in isolation and hence is important in counseling and prognosis. In fetuses with CLs, DTI would demonstrate normal or abnormal callosal architecture which is obscured by echogenicity and help in counseling.

Anomalies of the Corpus Callosum in Prenatal Ultrasound: A Narrative Review for Diagnosis and Further Counseling

The corpus callosum is the major interhemispheric tract that plays an important role in neurological function. Understanding the etiology and embryology development helps the ultrasound diagnosis for disorders of the corpus callosum and further counseling. The nonvisualization of cavum septum pellucidum or dysmorphic cavum septum pellucidum in axial view are indirect signs for beginners to diagnose complete agenesis of corpus callosum (cACC) and partial agenesis of the corpus callosum (pACC). Further coronal view, sagittal view, and fetal magnetic resonance imaging are also important for evaluation. Genetic testing plays an essential tool in anomalies of corpus callosum by revealing the underlying genetic pathophysiology, such as chromosomal anomalies and numerous monogenetic disorders in 30%-45% of ACC. Diagnosis and prediction of prognosis for hypoplasia or hyperplasia of the corpus callosum are more difficult compared to cACC and pACC because of the limited reports in the literature. However, the complex types often had poorer prognostic outcomes compared to the isolated types. Hence, it is important to evaluate and follow fetal conditions thoroughly to rule out intracranial or extracranial anomalies in other systems.

Assessment of fetal corpus callosum biometry by 3D super-resolution reconstructed T2-weighted magnetic resonance imaging

Objective

To assess the accuracy of corpus callosum (CC) biometry, including sub-segments, using 3D super-resolution fetal brain MRI (SR) compared to 2D or 3D ultrasound (US) and clinical low-resolution T2-weighted MRI (T2WS).

Method

Fetal brain biometry was conducted by two observers on 57 subjects [21-35 weeks of gestational age (GA)], including 11 cases of partial CC agenesis. Measures were performed by a junior observer (obs1) on US, T2WS and SR and by a senior neuroradiologist (obs2) on T2WS and SR. CC biometric regression with GA was established. Statistical analysis assessed agreement within and between modalities and observers.

Results

This study shows robust SR to US concordance across gestation, surpassing T2WS. In obs1, SR aligns with US, except for genu and CC length (CCL), enhancing splenium visibility. In obs2, SR closely corresponds to US, differing in rostrum and CCL. The anterior CC (rostrum and genu) exhibits higher variability. SR's regression aligns better with literature (US) for CCL, splenium and body than T2WS. SR is the method with the least missing values.

Conclusion

SR yields CC biometry akin to US (excluding anterior CC). Thanks to superior 3D visualization and better through plane spatial resolution, SR allows to perform CC biometry more frequently than T2WS.

Retrospective analysis of the prognostic factors of fetal corpus callosum dysplasia

BACKGROUND

To analyze the genetic characteristics and long-term outcomes of fetuses with dysplasia of the corpus callosum (DCC) or partial agenesis of the corpus callosum (PACC).

METHODS

A total of 42 fetuses with DCC (n = 36) or PACC (n = 6) were retrospectively analyzed from January 2016 to December 2022 at the Peking University First Hospital. The cohort was categorized into isolated (15/42, 36%) and nonisolated groups (27/42, 64%), and differences in the genetic abnormalities and long-term outcomes between the two groups were analyzed. DCC was subdivided into short CC, thin CC, and thick CC. The outcomes of the three different types of DCC were analyzed and discussed.

RESULTS

(1) Thirty-nine of the 42 cases underwent CMA (chromosomal microarray analysis) and CMA + WES (whole exome sequencing), with 13/15 cases in isolated group and 26/27 cases in nonisolated group. Only pathogenic or likely pathogenic (P/LP) variants were considered, identifying P/LP variants in 2/13 cases in isolated group and 12/26 cases in nonisolated group. There was no significant difference between the two groups (χ² = 3.566, P = 0.05897). (2) In the isolated group, 8 cases were terminated, and 7 cases were delivered. Postnatal follow-up detected 1 case of gross motor development delay one year after birth; no obvious abnormalities were found in the other six cases. In the nonisolated group, 21 cases were terminated, and 6 cases were delivered. Postnatal follow-up detected 4 cases of children with different degrees of language, motor and intelligence abnormalities; 1 case died 10 days after birth. No obvious abnormalities were observed in one case. Six cases (86%, 6/7) in the isolated group showed normal development, compared with 1 case (17%, 1/6) in the nonisolated group, with a significant difference (χ² = 6.198, P = 0.01279). (3) In DCC, the delivery rates of short CCs (18 cases), thin CCs (13 cases), and thick CCs (5 cases) were 17% (3/18), 54% (7/13), and 20% (1/5), respectively, with good outcomes observed in 0% (0/3), 71% (5/7), and 0% (0/1), respectively. P/LP variants were found in 6/17 cases of short CC, 3/12 cases of thin CC, and 2/5 cases of thick CC.

CONCLUSIONS

Fetuses with DCC or PACC combined with other structural abnormalities had a poor long-term prognosis compared with the isolated group. Patients with thin CCs had a higher probability of a good prognosis than those with short or thick CCs.

Corpus callosum in children with neurodevelopmental delay: MRI standard qualitative assessment versus automatic quantitative analysis

BACKGROUND

The corpus callosum (CC) is a key brain structure. In children with neurodevelopmental delay, we compared standard qualitative radiological assessments with an automatic quantitative tool.

METHODS

We prospectively enrolled 73 children (46 males, 63.0%) with neurodevelopmental delay at single university hospital between September 2020 and September 2022. All of them underwent 1.5-T brain magnetic resonance imaging (MRI) including a magnetization-prepared 2 rapid acquisition gradient echoes - MP2RAGE sequence. Two radiologists blindly reviewed the images to classify qualitatively the CC into normal, hypoplasic, hyperplasic, and/or dysgenetic classes. An automatic tool (QuantiFIRE) was used to provide brain volumetry and T1 relaxometry automatically as well as deviations of those parameters compared with a healthy age-matched cohort. The MRI reference standard for CC volumetry was based on the Garel et al. study. Cohen κ statistics was used for interrater agreement. The radiologists and QuantiFIRE's diagnostic accuracy were compared with the reference standard using the Delong test.

RESULTS

The CC was normal in 42 cases (57.5%), hypoplastic in 20 cases (27.4%), and hypertrophic in 11 cases (15.1%). T1 relaxometry values were abnormal in 26 children (35.6%); either abnormally high (18 cases, 24.6%) or low (8 cases, 11.0%). The interrater Cohen κ coefficient was 0.91. The diagnostic accuracy of the QuantiFIRE prototype was higher than that of the radiologists for hypoplastic and normal CC (p = 0.003 for both subgroups, Delong test).

CONCLUSIONS

An automated volumetric and relaxometric assessment can assist the evaluation of brain structure such as the CC, particularly in the case of subtle abnormalities.

RELEVANCE STATEMENT

Automated brain MRI segmentation combined with statistical comparison to normal volume and T1 relaxometry values can be a useful diagnostic support tool for radiologists.

KEY POINTS

• Corpus callosum abnormality detection is challenging but clinically relevant. • Automated quantitative volumetric analysis had a higher diagnostic accuracy than that of visual appreciation of radiologists. • Quantitative T1 relaxometric analysis might help characterizing corpus callosum better.

Neuronal nitric oxyde synthase positive neurons in human indusium griseum

The study was designed to analyze the nNOS positive neurons present in the indusium griseum by describing their distribution and morphology. To this purpose, sagittal serial sections from paraffin or frozen autopsy specimens of corpus callosum including the overlying indusium griseum were processed by immunohistochemistry and immunofluorescence, using an antibody against the neuronal form of the enzyme nitric oxyde synthase. To test the specificity of the antibody used, Western Blot was performed in the indusium griseum of the same specimens. The stainings revealed the presence of many neuronal nitric oxyde synthase-immunopositive neurons in human indusium griseum, located along both rostral-caudal and medio-lateral directions. In particular, they were more numerous 1 mm apart from the midline, and their number peaked over the body of the corpus callosum. They showed different morphologies; in some cases, they were located at the boundary between indusium griseum and corpus callosum, more densely packed in proximity to the pial arteries penetrating into the corpus callosum. The significant presence and distribution of neuronal nitric oxyde synthase-immunopositive neurons suggests that indusium griseum likely plays a functional role in the neurovascular regulation within the corpus callosum.