Lobar holoprosencephaly
Updates to Article Attributes
Lobar holoprosencephaly is a sub-type of holoprosencphaly, and is the least severe of the classical three sub-types, with both semilobar holoprosencephaly and alobar holoprosencephaly being worse.
As with all types of holoprosencephaly, it is a rare congenital brain malformation in which there is failure of complete separation of the two hemispheres and failure of transverse cleavage into diencephalon and telencephalon.
For a general discussion of epidemiology, clinical presentation and pathology, please refer to the article on holoprosencephaly.
Radiographic features
As will most cerebral structural congenital abnormalities, lobar holoprosencephaly is visible on all modalities, but in general is identified on antenatal ultrasound (if performed), and best characterised by MRI.
Unlike the more severe forms, in lobar holoprosencephaly the cerebral hemispheres are present. Features include 1-4:
- fusion of the frontal horns of the lateral ventricles
- wide communication of this fused segment with the third ventricle
- fusion of the
forniciesfornices 4 - absence of septum pellucidum
- agenesis or hypoplasia of the corpus callosum
Unlike semilobar holoprosencephaly, the falx is present, the interhemispheric fissure is fully formed and the thalami are not fused.
Differential diagnosis
-
semilobar holoprosencephaly
- fusion of the anterior aspects of the hemispheres
- falx and interhemispheric fissure incomplete
- partial fusion of the thalami
-
septooptic dysplasia
- can appear very similar
- fusion of the frontal lobes and of the
forniciesfornices is not a feature
-<li>fusion of the fornicies <sup>4</sup>- +<li>fusion of the fornices <sup>4</sup>
-<li>fusion of the frontal lobes and of the fornicies is not a feature</li>- +<li>fusion of the frontal lobes and of the fornices is not a feature</li>
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