Alobar holoprosencephaly
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Alobar holoprosencephaly is a subtype of holoprosencephaly and is the most severe of the classical three subtypes, with both semilobar and lobar holoprosencephaly having less severe clinical manifestations.
For a general discussion of epidemiology, clinical presentation, and pathology, please refer to the main article on holoprosencephaly.
Pathology
As with all types of holoprosencephaly, it is a rare congenital brain malformation in which there is a failure of complete separation of the two hemispheres (which usually occurs around the 4th to 6th gestational weeks) and failure of transverse cleavage into the diencephalon and telencephalon.
Radiographic features
As with most cerebral structural congenital abnormalities, alobar holoprosencephaly is visible on all modalities, but in general, is identified on antenatal ultrasound (if performed), and is best characterised by MRI.
Ultrasound
monoventricle
fused thalami
absent interhemispheric fissure
absence of 3rd ventricle
middle and anterior cerebral arteries may be replaced by tangled branches of internal carotid and basilar vessels
severe facial malformations
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
absent interhemispheric fissure and falxcerebri
absent olfactory tract
absent, fused or normal optic nerves
middle and anterior cerebral arteries may be replaced by tangled branches of internal carotid and basilar vessels
Associated craniofacial features may also be present which include:
The fused cortex can take on one of 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
Treatment and prognosis
This is the most severe type of the holoprosencephaly spectrum and often tends to be fatal in the neonatal period.
Differential diagnosis
-
partial separation into hemispheres
rudimentary occipital and temporal horns
-
thalami are often visible and are not fused
falx cerebri usually present
not associated with midline facial abnormalities
no cortex present, or sometimes small islands of tissue
-
severe hydrocephalus
falx cerebri 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 subtype of <a href="/articles/holoprosencephaly">holoprosencephaly</a> and is the most severe of the classical three subtypes, with both <a href="/articles/semilobar-holoprosencephaly-2">semilobar</a> and <a href="/articles/lobar-holoprosencephaly">lobar holoprosencephaly</a> having less severe clinical manifestations.</p><p>For a general discussion of epidemiology, clinical presentation, and pathology, please refer to the main article on <a href="/articles/holoprosencephaly">holoprosencephaly</a>.</p><h4>Pathology</h4><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> gestational weeks) and failure of transverse cleavage into the <a href="/articles/diencephalon">diencephalon</a> and <a href="/articles/telencephalon-1">telencephalon</a>.</p><h4>Radiographic features</h4><p>As with most cerebral structural congenital abnormalities, alobar holoprosencephaly is visible on all modalities, but in general is identified on antenatal ultrasound (if performed), and best characterised by MRI.</p><h5>Ultrasound</h5><ul>-<li>monoventricle</li>-<li>fused thalami</li>-<li><a href="/articles/dysgenesis-of-the-corpus-callosum">absent corpus callosum</a></li>-<li>absent <a href="/articles/interhemispheric-fissure">interhemispheric fissure</a>-</li>-<li>absent <a href="/articles/cavum-septum-pellucidum-3">cavum </a><a href="/articles/cavum-septum-pellucidum-3">septi</a><a href="/articles/cavum-septum-pellucidum-3"> </a><a href="/articles/cavum-septum-pellucidum-3">pellucidi</a>-</li>-<li>absence of <a href="/articles/third-ventricle">3<sup>rd</sup> ventricle</a>-</li>-<li>-<a href="/articles/middle-cerebral-artery">middle</a> and <a href="/articles/anterior-cerebral-artery">anterior cerebral arteries</a> may be replaced by tangled branches of <a href="/articles/internal-carotid-artery-1">internal carotid</a> and <a href="/articles/basilar-artery">basilar</a> vessels</li>-<li>severe facial malformations</li>- +<p><strong>Alobar holoprosencephaly</strong> is a subtype of <a href="/articles/holoprosencephaly">holoprosencephaly</a> and is the most severe of the classical three subtypes, with both <a href="/articles/semilobar-holoprosencephaly-2">semilobar</a> and <a href="/articles/lobar-holoprosencephaly">lobar holoprosencephaly</a> having less severe clinical manifestations.</p><p>For a general discussion of epidemiology, clinical presentation, and pathology, please refer to the main article on <a href="/articles/holoprosencephaly">holoprosencephaly</a>.</p><h4>Pathology</h4><p>As with all types of holoprosencephaly, it is a rare congenital brain malformation in which there is a failure of complete separation of the two hemispheres (which usually occurs around the 4<sup>th</sup> to 6<sup>th</sup> gestational weeks) and failure of transverse cleavage into the <a href="/articles/diencephalon">diencephalon</a> and <a href="/articles/telencephalon-1">telencephalon</a>.</p><h4>Radiographic features</h4><p>As with most cerebral structural congenital abnormalities, alobar holoprosencephaly is visible on all modalities, but in general, is identified on antenatal ultrasound (if performed), and is best characterised by MRI.</p><h5>Ultrasound</h5><ul>
- +<li><p>monoventricle</p></li>
- +<li><p>fused thalami</p></li>
- +<li><p><a href="/articles/dysgenesis-of-the-corpus-callosum">absent corpus callosum</a></p></li>
- +<li><p>absent <a href="/articles/interhemispheric-fissure">interhemispheric fissure</a></p></li>
- +<li><p>absent <a href="/articles/cavum-septum-pellucidum-3">cavum septi pellucidi</a></p></li>
- +<li><p>absence of <a href="/articles/third-ventricle">3<sup>rd</sup> ventricle</a></p></li>
- +<li><p><a href="/articles/middle-cerebral-artery">middle</a> and <a href="/articles/anterior-cerebral-artery">anterior cerebral arteries</a> may be replaced by tangled branches of <a href="/articles/internal-carotid-artery-1">internal carotid</a> and <a href="/articles/basilar-artery">basilar</a> vessels</p></li>
- +<li><p>severe facial malformations</p></li>
-<li>single midline monoventricle (or holosphere)<ul><li>-<a href="/articles/lateral-ventricle-1">lateral</a> and <a href="/articles/third-ventricle">third ventricles</a> are absent</li></ul>-</li>-<li>absent midline structures<ul>-<li>absent <a href="/articles/septum-pellucidum">septum pellucidum</a>-</li>-<li><a href="/articles/dysgenesis-of-the-corpus-callosum">agenesis or hypoplasia of the corpus callosum</a></li>-<li>absent <a href="/articles/interhemispheric-fissure">interhemispheric fissure</a> and <a href="/articles/falx-cerebri">falx</a><a href="/articles/falx-cerebri"> </a><a href="/articles/falx-cerebri">cerebri</a>- +<li>
- +<p>single midline monoventricle (or holosphere)</p>
- +<ul><li><p><a href="/articles/lateral-ventricle-1">lateral</a> and <a href="/articles/third-ventricle">third ventricles</a> are absent</p></li></ul>
-<li>absent olfactory tract</li>- +<li>
- +<p>absent midline structures</p>
- +<ul>
- +<li><p>absent <a href="/articles/septum-pellucidum">septum pellucidum</a></p></li>
- +<li><p><a href="/articles/dysgenesis-of-the-corpus-callosum">agenesis or hypoplasia of the corpus callosum</a></p></li>
- +<li><p>absent <a href="/articles/interhemispheric-fissure">interhemispheric fissure</a> and <a href="/articles/falx-cerebri">falx cerebri</a></p></li>
- +<li><p>absent olfactory tract</p></li>
-<li><a href="/articles/dorsal-cyst-of-holoprosencephaly">dorsal cyst of holoprosencephaly</a></li>-<li>absent, fused or normal optic nerves</li>-<li>middle and anterior cerebral arteries may be replaced by tangled branches of internal carotid and basilar vessels</li>- +<li><p><a href="/articles/dorsal-cyst-of-holoprosencephaly">dorsal cyst of holoprosencephaly</a></p></li>
- +<li><p>absent, fused or normal optic nerves</p></li>
- +<li><p>middle and anterior cerebral arteries may be replaced by tangled branches of internal carotid and basilar vessels</p></li>
-<li><a href="/articles/proboscis">proboscis</a></li>-<li>-<a href="/articles/mono-orbit">mono-orbit</a>/<a href="/articles/cyclopia">cyclopia</a>-</li>-<li><a href="/articles/mono-nostril">mononostril</a></li>-<li><a href="/articles/hypotelorism">hypotelorism</a></li>-<li><a href="/articles/cebocephaly">cebocephaly</a></li>- +<li><p><a href="/articles/proboscis">proboscis</a></p></li>
- +<li><p><a href="/articles/mono-orbit">mono-orbit</a>/<a href="/articles/cyclopia">cyclopia</a></p></li>
- +<li><p><a href="/articles/mono-nostril">mononostril</a></p></li>
- +<li><p><a href="/articles/hypotelorism">hypotelorism</a></p></li>
- +<li><p><a href="/articles/cebocephaly">cebocephaly</a></p></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>- +<li><p>pancake: cerebral tissue is confined to the anterior basicranium</p></li>
- +<li><p>cup: cerebral tissue lines variable amounts of the anterior cranium with a dorsal cyst present posteriorly</p></li>
- +<li><p>ball: a complete rim of tissue surrounds the monoventricle without dorsal cyst</p></li>
-<a href="/articles/semilobar-holoprosencephaly-2">semilobar holoprosencephaly</a><ul>-<li>partial separation into hemispheres</li>-<li>rudimentary occipital and temporal horns</li>- +<p><a href="/articles/semilobar-holoprosencephaly-2">semilobar holoprosencephaly</a></p>
- +<ul>
- +<li><p>partial separation into hemispheres</p></li>
- +<li><p>rudimentary occipital and temporal horns</p></li>
-<a href="/articles/hydranencephaly">hydranencephaly</a><ul>-<li>thalami are often visible and are not fused</li>-<li>falx cerebri usually present</li>-<li>not associated with midline facial abnormalities</li>-<li>no cortex present, or sometimes small islands of tissue</li>- +<p><a href="/articles/hydranencephaly">hydranencephaly</a></p>
- +<ul>
- +<li><p>thalami are often visible and are not fused</p></li>
- +<li><p>falx cerebri usually present</p></li>
- +<li><p>not associated with midline facial abnormalities</p></li>
- +<li><p>no cortex present, or sometimes small islands of tissue</p></li>
-<li>severe <a href="/articles/obstructive-hydrocephalus">hydrocephalus</a><ul>-<li>falx cerebri usually present, but may be absent due to severe long-standing hydrocephalus</li>-<li>bilateral choroid plexus</li>-<li>thalami not fused</li>-<li>not associated with midline facial abnormalities</li>- +<li>
- +<p>severe <a href="/articles/obstructive-hydrocephalus">hydrocephalus</a></p>
- +<ul>
- +<li><p>falx cerebri usually present, but may be absent due to severe long-standing hydrocephalus</p></li>
- +<li><p>bilateral choroid plexus</p></li>
- +<li><p>thalami not fused</p></li>
- +<li><p>not associated with midline facial abnormalities</p></li>
References changed:
- 1. McGahan J, Nyberg D, Mack L. Sonography of Facial Features of Alobar and Semilobar Holoprosencephaly. AJR Am J Roentgenol. 1990;154(1):143-8. <a href="https://doi.org/10.2214/ajr.154.1.2104699">doi:10.2214/ajr.154.1.2104699</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/2104699">Pubmed</a>
- 2 . Dario Paladini, Paolo Volpe. Ultrasound of Congenital Fetal Anomalies. (2007) ISBN: 9780415414449 - <a href="http://books.google.com/books?vid=ISBN9780415414449">Google Books</a>
- 3. Filly R, Chinn D, Callen P. Alobar Holoprosencephaly: Ultrasonographic Prenatal Diagnosis. Radiology. 1984;151(2):455-9. <a href="https://doi.org/10.1148/radiology.151.2.6709918">doi:10.1148/radiology.151.2.6709918</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/6709918">Pubmed</a>
- 4. Castillo M, Bouldin T, Scatliff J, Suzuki K. Radiologic-Pathologic Correlation. Alobar Holoprosencephaly. AJNR Am J Neuroradiol. 1993;14(5):1151-6. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8332773">PMC8332773</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/8237694">Pubmed</a>
- 1. Mcgahan JP, Nyberg DA, Mack LA. Sonography of facial features of alobar and semilobar holoprosencephaly. AJR Am J Roentgenol. 1990;154 (1): 143-8. <a href="http://www.ajronline.org/cgi/content/abstract/154/1/143">AJR Am J Roentgenol (abstract)</a> - <a href="http://www.ncbi.nlm.nih.gov/pubmed/2104699">Pubmed citation</a><div class="ref_v2"></div>
- 2 . Paladini D, Volpe P. Ultrasound of Congenital Fetal Anomalies. Informa HealthCare. (2007) ISBN:041541444X. <a href="http://books.google.com/books?vid=ISBN041541444X">Read it at Google Books</a> - <a href="http://www.amazon.com/gp/product/041541444X?ie=UTF8&tag=radiopaediaor-20&linkCode=as2&camp=1789&creative=9325&creativeASIN=041541444X">Find it at Amazon</a><div class="ref_v2"></div>
- 3. Filly RA, Chinn DH, Callen PW. Alobar holoprosencephaly: ultrasonographic prenatal diagnosis. Radiology. 1984;151 (2): 455-9. <a href="http://radiology.rsna.org/content/151/2/455.abstract">Radiology (abstract)</a> - <a href="http://www.ncbi.nlm.nih.gov/pubmed/6709918">Pubmed citation</a><div class="ref_v2"></div>
- 4. Castillo M, Bouldin TW, Scatliff JH et-al. Radiologic-pathologic correlation. Alobar holoprosencephaly. AJNR Am J Neuroradiol. 14 (5): 1151-6. <a href="http://www.ajnr.org/cgi/content/citation/14/5/1151">AJNR Am J Neuroradiol (citation)</a> - <a href="http://www.ncbi.nlm.nih.gov/pubmed/8237694">Pubmed citation</a><div class="ref_v2"></div>
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