ABSTRACT
There are different forms of cerebral commissure malformations, depending on abnormalities of developmental processes. The anomalies of cerebral commissures are as follows:
1. Complete agenesis of all cerebral commissures (Figure 21.1a and b)
Elzbieta Jurkiewicz and Katarzyna Nowak
CONTENTS
21.1 Cerebral Commissure Anomalies .......................................................................................................................... 553 21.1.1 Commissural Abnormalities/Dysgenesis and Meningeal Dysplasia (Formerly: Agenesis
of the Corpus Callosum with Interhemispheric Cyst) ........................................................................ 554 21.2 Holoprosencephaly ................................................................................................................................................... 556 21.3 Septo-Optic Dysplasia .............................................................................................................................................. 557 21.4 Schizencephaly .......................................................................................................................................................... 561 21.5 Lissencephaly ............................................................................................................................................................ 564
21.5.1 Pachygyria or Incomplete Lissencephaly .............................................................................................. 565 21.6 Microcephaly ............................................................................................................................................................. 566 21.7 The Cobblestone Malformation-Cobblestone Lissencephaly (Formerly: Lissencephaly Type 2) ............... 570 21.8 Polymicrogyria .......................................................................................................................................................... 571 21.9 Hemimegalencephaly .............................................................................................................................................. 573 21.10 Heterotopia .................................................................................................................................................................574 21.11 Focal Cortical Dysplasia .......................................................................................................................................... 575 21.12 Cerebellar Hypoplasia ............................................................................................................................................. 576 21.13 Pontocerebellar Hypoplasia .................................................................................................................................... 579 21.14 Dandy-Walker Malformation ................................................................................................................................. 580 21.15 Cerebellar Cortical Dysgenesis-Focal or Diffuse .............................................................................................. 583 21.16 Molar Tooth Syndrome (Joubert Syndrome and Related Disorders) ................................................................ 584 21.17 Brain-Stem Disconnection Syndrome (Pontomedullary Disconnection) ......................................................... 584 21.18 Rhombencephalosynapsis ....................................................................................................................................... 585 21.19 Malformations of the Pons and Medulla ............................................................................................................... 590
21.19.1 Pontine Tegmental Cap Dysplasia .......................................................................................................... 590 21.19.2 Medullary Cap Dysplasia ........................................................................................................................ 590
21.20 Chiari Malformations ............................................................................................................................................... 592 21.21 Cephalocele ................................................................................................................................................................ 594 21.22 Intracranial Lipoma .................................................................................................................................................. 599 21.23 Arachnoid Cysts ........................................................................................................................................................ 604 Bibliography ............................................................................................................................................................................ 608
2. Classic callosal agenesis-agenesis of corpus callosum and hippocampal commissures with visible anterior commissure (Figures 21.2a, 21.3a-c, and 21.4)
3. Partial agenesis of corpus callosum-agenesis of the posterior part of corpus callosum and hippocampal commissures with anterior commissure being visible or not (Figure 21.5)
4. Posterior callosal hypogenesis with callosal tapering. Anterior and hippocampal commissures may be normal (Figure 21.6a-c)
The common imaging characteristics associated with agenesis of the corpus callosum are as follows: absent cingulate gyrus, radially oriented medial hemispheric sulci that reach the third ventricle, high-riding third ventricle open superiorly to the interhemispheric fissure, lateral ventricles parallel to each other with dilatation of the atrium and occipital horn (colpocephaly), dilated temporal horns with incomplete rotation and abnormal shape of the hippocampi, a bull’s horn appearance of the lateral ventricles on coronal views (Figure 21.2b), Probst bundles in most cases, and sometimes sigmoid bundle can be seen (Figure 21.2c and d).
