<%server.execute "isdev.asp"%> Magnetic resonance imaging findings in fetal corpus callosal developmental abnormalities: A pictorial essay Manor C, Rangasami R, Suresh I, Suresh S - J Pediatr Neurosci
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REVIEW ARTICLE
Year : 2020  |  Volume : 15  |  Issue : 4  |  Page : 352-357
 

Magnetic resonance imaging findings in fetal corpus callosal developmental abnormalities: A pictorial essay


1 Department of Radiology, Sri Ramachandra Institute of Higher Education and Research (DU), Chennai, Tamil Nadu, India
2 Department of Fetal Medicine, Mediscan Systems, Chennai, Tamil Nadu, India

Date of Submission29-Dec-2019
Date of Acceptance19-Mar-2020
Date of Web Publication19-Jan-2021

Correspondence Address:
Dr. Rajeswaran Rangasami
Department of Radiology and Imaging Sciences, Sri Ramachandra Institute of Higher Education and Research, Chennai 600116, Tamil Nadu.
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/JPN.JPN_174_19

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   Abstract 

The corpus callosum is the principal supratentorial cerebral commissure, which connects the two cerebral hemispheres in the midline. It is divided into rostrum, genu, body, and splenium. Affected patients may develop mental retardation, dysmorphic features, spasticity, ataxia, or epilepsy. Corpus callosal abnormalities may be isolated or be associated with other anomalies such as sulcal abnormality, ventriculomegaly, cerebellar hypoplasia or cerebellar vermian hypoplasia. Magnetic resonance imaging (MRI) plays a major role in the diagnosis of fetal corpus callosal developmental abnormalities when they are suspected on sonography. This pictorial essay shows the MRI findings in fetal corpus callosal developmental abnormalities in a very systematic manner.


Keywords: Agenesis of corpus callosum, anomalies, corpus callosum, partial agenesis of corpus callosum, fetal MRI


How to cite this article:
Manor C, Rangasami R, Suresh I, Suresh S. Magnetic resonance imaging findings in fetal corpus callosal developmental abnormalities: A pictorial essay. J Pediatr Neurosci 2020;15:352-7

How to cite this URL:
Manor C, Rangasami R, Suresh I, Suresh S. Magnetic resonance imaging findings in fetal corpus callosal developmental abnormalities: A pictorial essay. J Pediatr Neurosci [serial online] 2020 [cited 2021 Feb 27];15:352-7. Available from: https://www.pediatricneurosciences.com/text.asp?2020/15/4/352/307364





   Introduction Top


The corpus callosum (CC) is the principal supratentorial cerebral commissure. Adjacent to the CC, there are two other smaller interhemispheric fissure connections, namely the anterior commissure and the hippocampal commissure.[1] Fetal corpus callosal abnormalities (CCA) may occur due to genetic causes, intrauterine infection, vitamin deficiency, vascular and unknown causes. A number of genetic disorders in humans have been associated with CCA, including several X-linked diseases, metabolic disorders and contiguous gene deletion syndromes.[2] Magnetic resonance imaging (MRI) is the modality of choice in the assessment of fetal CC due to its multiplanar capability and contrast resolution. As there are several CCA, it is important to view the CC in all the three planes on MRI before making a diagnosis.


   Anatomy and Embryology Top


The CC is the principal supratentorial cerebral commissure made up of white matter tracts tightly packed to connect the two cerebral hemispheres in the midline. It consists of more than 200–250 million myelinated axons that cross the midline in the developing brain to connect the two hemispheres. The CC is divided into four parts (anterior to posterior): (1) rostrum, (2) genu, (3) body, and (4) splenium. The sequence of CC development begins with the differentiation of the commissural plate around six gestation weeks (GW), followed by crossing of pioneer axons.[2] During the 8th to the 14th gestational weeks, callosal precursors and the cortical fibers of bilateral cerebral hemispheres develop to form the CC, it begins with the development of genu anteriorly and proceeds to the splenium posteriorly except for the rostrum, which is the last area that is seen to show crossed fibers.[3],[4] The final shape is reached by 19–20 weeks [Figure 1], though it keeps growing to reach a good volume by 6–9 years. The myelination of CC occurs only after birth and is not complete until adolescence. Owing to defect in embryological development, CCA can be isolated or can occur in combination with other anomalies.
Figure 1: Sagittal and axial MR images of normal corpus callosum at 18 weeks (A, E), 20 weeks (B, F), 24 weeks (C, G), 30 weeks (D, H)

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   Discussion Top


Terminologies used to discuss CCA are heterogeneous. Some authors just described partial and complete agenesis. Then it was refined as agenesis, hypogenesis, and dysgenesis. Hanna et al.[5] further refined CCA and divided them into four principal classes as follows:

  • Hypoplasia
    • - Hypoplasia without dysplasia


    • - Apple core CCA


    • - Anterior remnant CCA


  • Dysplasia without hypoplasia


  • Hypoplasia with dysplasia
    • - Stripe CCA


    • - Kinked CCA


  • Complete agenesis


  • We reviewed the various fetal corpus callosal morphological abnormalities encountered during November 2014 to October 2018 in our institution and have discussed them [Figure 2]. These 10 fetuses did not have any consanguineous background. We have tried to display the various morphological abnormalities that can occur in CC irrespective of the etiology. Of the 10 fetuses, six couples opted for termination and four were managed conservatively. The diagnosis was confirmed by postnatal imaging in the four conservatively managed cases. In the terminated six fetuses, the diagnosis was confirmed by autopsy in four cases. Two couples did not consent for fetal autopsy. The MR images of these two fetuses were read independently by two senior fetal imaging specialists, and the final diagnosis was arrived by consensus.
    Figure 2: Graphic representation of CCA. (A) Normal. (B) Hypoplasia without dysplasia. (C) Apple core hypoplasia. (D) Anterior remnant hypoplasia. (E) Dysplasia. (F) Hypoplasia with dysplasia: Stripe (G) Hypoplasia with dysplasia: Kinked (H) Mega CC

    Click here to view


    Hypoplasia

    Hypoplasia consists of uniformly thin or underdeveloped CC in the posterior region [Figure 3]. It has three subtypes: hypoplasia without dysplasia, apple core CCA, and anterior remnant CCA.[5] The normal thickness and measurements of CC at various gestational age have been discussed by Pashaj et al.[6]
    Figure 3: Axial (A, B) MR image of a 21-week fetus shows absent splenium of CC, rhombencephalensynapsis (arrows) besides ventriculomegaly (arrowhead). Sagittal image (C) shows absent splenium of CC (open arrow)—hypoplasia without dysplasia

    Click here to view


    Hypoplasia without dysplasia

    In this, the caliber of the CC is reduced, but has all major anatomic features intact, including a distinctive rostrum, genu, corpus, and splenium[5] [Figure 4].
    Figure 4: Axial (A, B) MR image of a 32-week fetus shows thin genu and splenium of CC (arrows) besides colpocephaly sagittal image (C) shows uniformly thin CC (open arrow). Postnatal ultrasound image taken at 2 months confirms uniformly thin CC (arrowhead)

    Click here to view


    Apple core CCA

    More severe forms of hypoplasia show progressive loss of the more caudal aspects of the CC. This includes a form where the posterior CC is hypoplastic and foreshortened (i.e., corpus or splenium), taking on the appearance of an apple core CCA [Figure 5].
    Figure 5: Axial (A) MR image of a 28-week fetus shows a normal cavum septum pellucidum (arrows). The splenium is not visualized. Sagittal image (B) shows thinning of CC in the posterior third (open arrow) suggesting apple core hypoplasia without dysplasia. Postnatal ultrasound image taken at 2 weeks confirms thinning of CC in the posterior third (arrowhead)

    Click here to view


    Anterior remnant CCA

    In this subtype, there is agenesis of the posterior CC (i.e., corpus and splenium) called anterior remnant CCA type [Figure 6].
    Figure 6: Axial (A) MR image of a 23-week fetus shows an absent cavum septum pellucidum. The genu is visualized (arrows). Sagittal image (B) shows the anterior remnant hypoplastic CC (arrowhead) and absence in the posterior two-third. Sagittal image (C) shows associated vermian hypoplasia with brain stem vermian angle of 38°

    Click here to view


    Dysplasia without hypoplasia

    Dysplasia means that the development of the CC has occurred but is malformed.[5] This type encompasses cases in which the CC is morphologically abnormal [Figure 7].
    Figure 7: Axial (A) MR image of a 22-week fetus shows bridging tissue in the region of mid-body of CC (arrows). Sagittal image (B) shows presence of a dysplastic CC in the mid-body (arrowhead)

    Click here to view


    Hypoplasia with dysplasia

    In this class of CCA—hypoplasia with dysplasia—there is disturbance of the overall shape of the CC that is not limited to the posterior region.[5] It has two subtypes—stripe CCA and kinked CCA.

    Stripe CCA

    This type consists of a uniform thin stripe CCA that lacks an anatomically distinct genu and splenium [Figure 8].
    Figure 8: Axial (A) MR image of a 29-week fetus shows absent cavum septum pellucidum and genu, the splenium is visualized (arrows). Sagittal image (B) shows diffuse thinning of CC (arrowhead) with absent genu suggesting stripe CCA—hypoplasia with dysplasia. Postnatal MRI image taken at 7 months confirms thinning of CC with absent genu (arrowhead)

    Click here to view


    Kinked CCA

    This type is characterized by a CC that is hypoplastic as well as obviously kinked at one or more locations, either anteriorly or posteriorly, and is called kinked CCA [Figure 9].
    Figure 9: Axial (A, B), sagittal (C) MR image of a 25-week fetus shows the presence of a kinked hypoplastic–dysplastic CC (arrows) and an interhemispheric cyst posteriorly (open arrow). There is also poor sulcation seen

    Click here to view


    Complete agenesis

    The next class of CCA is characterized by absent CC as seen on a midline sagittal MR image [Figure 10]. In this class, it is important to distinguish the hippocampal commissure from the CC, the former retained in many complete agenesis cases.[7]
    Figure 10: Axial (A) MR image of a 22-week fetus shows absent septum, CC, and colpocephaly (arrows). Sagittal image (B) confirms absent CC

    Click here to view


    Agenesis of the CC is one of the common central nervous system malformations. CC agenesis may occur as an isolated lesion. But it is more commonly seen in association with a variety of other central nervous system malformations or malformations of other organ systems. The lack of commissural fibers crossing the midline is a primary feature of this anomaly. There is an ipsilateral migration of the uncrossed fibers, coursing along the superomedial region of the lateral ventricles to form a structure called Probst bundles.[8]

    The pathologic changes produced by CC agenesis in the cerebral hemispheres include absent or malformed CC, cingulate gyrus and sulcus. The changes seen in the ventricular system include a high-riding third ventricle, which opens to the interhemispheric fissure superiorly. A radial or “spoke-like” configuration of the sulci and gyri around the third ventricle is seen on the medial hemispheric surface. A dorsal cyst may occasionally be present in this space. There is displacement of the lateral cerebral ventricles superiorly and laterally. In most cases, on axial sections of the brain, a disproportionate dilatation of the occipital horns of the bilateral lateral ventricles called as colpocephaly may be seen.[9]

    Mega corpus callosum

    Mega corpus callosum (MCC) is extremely rare unlike agenesis and hypoplasia. It may present as an isolated anomaly or be associated with abnormalities such as megalencephaly and polymicrogyria. In this condition, the dimensions of the CC are increased uniformly [Figure 11]. It is postulated that the thickening is due to the persistence of anomalous longitudinal midline supracallosal fibers, which usually disappear during axonal migration.[10]
    Figure 11: Axial (A) and sagittal (B) MR image shows an uniformly thickened CC (arrows)

    Click here to view


    CCA with interhemispheric cyst

    Interhemispheric cysts are encountered in 7% of the patients diagnosed with CC agenesis.[8] The origin of the interhemispheric cyst in cases of CC agenesis is controversial. Suggested possible causes are arachnoid, neurenteric and ependymal cysts. Barkovich et al.[11] classified interhemispheric cysts, based on morphology into two major types. Type 1 cysts are unilocular and appear to be a diverticulum of the third or the lateral ventricle. Type 2 cysts are multilocular, and there is no communication with the ventricular system [Figure 9].[11]

    CCA with pericallosal lipoma

    A pericallosal lipoma is relatively common in partial or complete agenesis of the CC [Figure 12]. The size of the lipoma ranges from less than a centimeter to a large mass. Sometimes, it is seen as an ovoid mass, thin streak, or two longitudinal columns showing a central groove.[12] Pericallosal region is one of the most common sites and accounts to about one-third of intracranial lipomas. A size-dependent association of either partial or complete corpus callosal agenesis has been encountered in over 50% of cases with pericallosal lipoma. A larger lipoma may produce mass effect, causing displacement and an alteration in the shape of the CC. In CC agenesis, the lipoma fills in the normal anatomical location of the CC but does not infiltrate it. The region adjacent to the dorsal callosal surface is the most common site of involvement.[13] On MRI, the lipoma of the CC are T1 and T2 hyperintense well-marginated fat signal intensity masses, which show attenuation on fat suppression sequences.
    Figure 12: Axial (A, B) T2-weighted MR image shows bridging tissue in the region of genu of CC (arrows). Bilateral ventriculomegaly and colpocephaly are present. Axial (C) T1-weighted MR image showing hyperintensity within the bridging tissue suggesting agenesis of CC with associated lipoma

    Click here to view



       Associated Anomalies Top


    The common associated anomalies occurring with CCA are sulcal abnormality, ventriculomegaly, cerebellar hypoplasia, cerebellar vermian hypoplasia [Figure 6], Dandy Walker malformation and holoprosencephaly.[13],[14]

    The definitive diagnosis of CCA can be made by ultrasound, if a midsagittal plane parallel to the CC could be obtained. But due to fetal position, it is rarely obtained and hence three-dimensional ultrasound comes handy to provide the plane that is needed once a volume of fetal head is obtained.[15] MRI is a complementary modality to sonography in the assessment of fetal CC due to its multiplanar capability and contrast resolution. It is recommended to view fetal CC in all the three planes to avoid errors in interpretation. MRI is also useful in identifying associated anomalies, which can help in patient counseling.

    Acknowledgement

    We thank Dr. R. Rajkali for his illustrative diagram.

    Financial support and sponsorship

    Nil.

    Conflicts of interest

    There are no conflicts of interest.



     
       References Top

    1.
    Hetts SW, Sherr EH, Chao S, et al. Anomalies of the corpus callosum: an MR analysis of the phenotypic spectrum of associated malformations. Am J Roentgenol 2006;187:1343-8.  Back to cited text no. 1
        
    2.
    Richards LJ, Plachez C, Ren T Mechanisms regulating the development of the corpus callosum and its agenesis in mouse and human. Clin Genet 2004;66:276-89.  Back to cited text no. 2
        
    3.
    Lee SK, Kim DI, Kim J, Kim DJ, Kim HD, Kim DS, et al. Diffusion-tensor MR imaging and fiber tractography: a new method of describing aberrant fiber connections in developmental CNS anomalies. Radiographics 2005;25:53-65; discussion 66-8.  Back to cited text no. 3
        
    4.
    Georgy BA, Hesselink JR, Jernigan TL, et al. MR imaging of the corpus callosum. AJR Am J Roentgenol 1993;160:949-55.  Back to cited text no. 4
        
    5.
    Hanna RM, Marsh SE, Swistun D, Al-Gazali L, Zaki MS, Abdel-Salam GM, et al. Distinguishing 3 classes of corpus callosal abnormalities in consanguineous families. Neurology 2011;76:373-82.  Back to cited text no. 5
        
    6.
    Pashaj S, Merz E, Wellek S Biometry of the fetal corpus callosum by three-dimensional ultrasound. Ultrasound Obstet Gynecol 2013;42:691-8.  Back to cited text no. 6
        
    7.
    Barkovich AJ, et al. Pediatric neuroimaging. Philadelphia, PA: Lippincott Williams & Wilkins; 2005.  Back to cited text no. 7
        
    8.
    Battal B, Kocaoglu M, Akgun V, Bulakbasi N, Tayfun C Corpus callosum: normal imaging appearance, variants and pathologic conditions. J Med Imaging Radiat Oncol 2010;54:541-9.  Back to cited text no. 8
        
    9.
    Sangram S, Garge S, et al. “Agenesis of the corpus callosum”. J Pediatr Neurosci 2010;5:83-5.  Back to cited text no. 9
        
    10.
    Jaisankar PK, Rangasami R MR imaging and MR diffusion tensor imaging in mega corpus callosum. Neurol India 2015;63:997-8.  Back to cited text no. 10
        
    11.
    Barkovich AJ, Simon EM, Walsh CA Callosal agenesis with cyst: a better understanding and new classification. Neurology 2001;56:220-7.  Back to cited text no. 11
        
    12.
    Nordin WA, Tesluk H, Jones RK Lipoma of the corpus callosum. AMA Arch Neurol Psychiatry 1955;74:300-7.  Back to cited text no. 12
        
    13.
    Curnes JT, Wayne Laster D, Koubek TD, et al. MRI of corpus callosal syndromes. AJNR1986;7:617-22.  Back to cited text no. 13
        
    14.
    Bourekas EC, Varakis K, Bruns D, Christoforidis GA, Baujan M, Slone HW, et al. Lesions of the corpus callosum: MR imaging and differential considerations in adults and children. AJR Am J Roentgenol 2002;179:251-7.  Back to cited text no. 14
        
    15.
    Plasencia W, Dagklis T, Borenstein M, Csapo B, Nicolaides KH Assessment of the corpus callosum at 20-24 weeks’ gestation by three-dimensional ultrasound examination. Ultrasound Obstet Gynecol 2007;30:169-72.  Back to cited text no. 15
        


        Figures

      [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12]



     

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        Abstract
       Introduction
        Anatomy and Embr...
       Discussion
       Associated Anomalies
        References
        Article Figures

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