Alobar holoprosencephaly
Updates to Article Attributes
Alobar holoprosencephaly is a sub type of holoprosencephaly, and is the most severe of the classical three sub types, with both semilobar holoprosencephaly and lobar holoprosencephaly being better.
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 (which usually occurs around the 4th to 6th weeks) 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.
MRI
The basic structure of the cerebral hemispheres is lost, with variable amounts of residual cortex. Features include 1-2:
- single midline monoventricle (or holosphere)
- lateral and third ventricles are absent
- absent midline structures
- absent septum pellucidum
- agenesis or hypoplasia of the corpus callosum
- absent interhemispheric fissure and falx cerebri
- dorsal cyst of holoprosencephaly
Associated craniofacial features may also be present which include
The fused cortex can take on three basic shapes 2:
- pancake: cerebral tissue is confined to the anterior basicranium
- cup: cerebral tissue lines variable amounts of the anterior cranium with a dorsal cyst present posteriorly
- ball: a complete rim of tissue surrounds the monoventricle without dorsal cyst
Prognosis
This is the most severe of the holoprosencephaly spectrum and often tends to be fatal in the neonatal period.
Differential diagnosis
-
semilobar holoprosencephaly
- partial separation into hemispheres
- rudimentary occipital and temporal horns
-
hydranencephaly
- thalami are often visible and are not fused
- not associated with midline facial abnormalities
- no cortex present, or sometimes small islands of tissue
- severe hydrocephalus
- falx usually present, but may be absent due to severe long-standing hydrocephalus
- bilateral choroid plexus
- thalami not fused
- not associated with midline facial abnormalities
-<p><strong>Alobar holoprosencephaly</strong> is a sub type of <a href="/articles/holoprosencephaly">holoprosencephaly</a>, and is the most severe of the classical three sub types, with both <a href="/articles/semi-lobar-holoprosencephaly">semilobar holoprosencephaly</a> and <a href="/articles/lobar-holoprosencephaly">lobar holoprosencephaly</a> being better. </p><p>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 (which usually occurs around the 4<sup>th</sup> to 6<sup>th</sup> weeks) and failure of transverse cleavage into <a href="/articles/diencephalon">diencephalon</a> and <a href="/articles/telencephalon">telencephalon</a>.</p><p>For a general discussion of epidemiology, clinical presentation and pathology, please refer to the article on <a href="/articles/holoprosencephaly">holoprosencephaly</a>. </p><h4>Radiographic features</h4><p>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. </p><h5>MRI</h5><p>The basic structure of the cerebral hemispheres is lost, with variable amounts of residual cortex. Features include <sup>1-2 </sup>:</p><ul>- +<p><strong>Alobar holoprosencephaly</strong> is a sub type of <a href="/articles/holoprosencephaly">holoprosencephaly</a>, and is the most severe of the classical three sub types, with both <a href="/articles/semi-lobar-holoprosencephaly">semilobar holoprosencephaly</a> and <a href="/articles/lobar-holoprosencephaly">lobar holoprosencephaly</a> being better. </p><p>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 (which usually occurs around the 4<sup>th</sup> to 6<sup>th</sup> weeks) and failure of transverse cleavage into <a href="/articles/diencephalon">diencephalon</a> and <a href="/articles/telencephalon">telencephalon</a>.</p><p>For a general discussion of epidemiology, clinical presentation and pathology, please refer to the article on <a href="/articles/holoprosencephaly">holoprosencephaly</a>. </p><h4>Radiographic features</h4><p>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. </p><h5>MRI</h5><p>The basic structure of the cerebral hemispheres is lost, with variable amounts of residual cortex. Features include <sup>1-2</sup>:</p><ul>
-<li>-<strong>pancake</strong> : cerebral tissue is confined to the anterior basicranium</li>-<li>-<strong>cup</strong> : cerebral tissue lines variable amounts of the anterior cranium with a dorsal cyst present posteriorly</li>-<li>-<strong>ball </strong>: a complete rim of tissue surrounds the monoventricle without dorsal cyst</li>- +<li>pancake: cerebral tissue is confined to the anterior basicranium</li>
- +<li>cup: cerebral tissue lines variable amounts of the anterior cranium with a dorsal cyst present posteriorly</li>
- +<li>ball: a complete rim of tissue surrounds the monoventricle without dorsal cyst</li>
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