CASE 17438 Published on 11.10.2021

A case report on syntelencephaly: A rare variant of holoprosencephaly

Section

Paediatric radiology

Case Type

Clinical Cases

Authors

Dr Anshul Ghai1, Dr Shubham Khunger2

1. B. J. Medical College, Ahmedabad, India

2. Vardhaman Mahavir Medical college and Safdarjung Hospital, New Delhi, India

Patient

4 years, male

Categories
Area of Interest CNS, Paediatric ; Imaging Technique MR
Clinical History

A 4-years-old male presented with a history of global developmental delay with a delayed achievement of walking without support and speech. There was no significant antenatal history however there was a history of two minutes delayed cry at birth.

Imaging Findings
  • There was partial cleavage of the cerebral hemispheres with fusion of the middle aspect of the grey & white matter of postero-superior part of bilateral frontal lobes and anterior part of the bilateral parietal lobes across the midline.
  • There was partial agenesis of corpus callosum as the body of the corpus callosum was not visualized. The genu and splenium of the corpus callosum were visualized and appeared normal in morphology & signal intensity.
  • The septum pellucidum was not visualized.
  • The frontal horns and body of bilateral lateral ventricles were fused.
  • The lateral ventricle was abutted anteriorly & posteriorly by multiple nodules following grey matter signal intensity on all sequences suggestive of nodular heterotopia. A grey matter nodule was seen perched on top of the fused ventricle indenting it.
  • Bilateral ACA were fused to form a single azygous ACA.
Discussion

The overall incidence of holoprosencephaly varies from 1:10000 live births to 1:250 aborted fetuses.[3,4]

Holoprosencephaly is a rare congenital malformation of the brain due to the failure of bifurcation of the two cerebral hemispheres. Several variants of holoprosencephaly have been identified which are alobar holoprosencephaly, semilobar holoprosencephaly, lobar holoprosencephaly, syntelencephaly [9], septopreoptic holoprosencephaly, [10] solitary median maxillary central incisor syndrome [10] and congenital nasal pyriform aperture stenosis [10].

Alobar holoprosencephaly: The brain is often small in size, agyric or mildly sulcated with flat pancake or ball-like configuration [13]. There is no falx cerebri, no interhemispheric fissure, no septum pellucidum, fused bilateral basal ganglia [11], agenesis of corpus callosum [13]. There is a single crescent-shaped monoventricle that communicates dorsally into a large CSF filled dorsal cyst [13].

Semilobar holoprosencephaly: There is fusion of anterior aspect of the bilateral cerebral hemispheres, rudimentary falx cerebri and IHF, absence of genu and body of corpus callosum, absent septum pellucidum,[11] fused bilateral basal ganglia [13] and absent frontal horns [11].

Lobar holoprosencephaly: There is fusion of most anterior and ventral part of the bilateral frontal lobes with rest of the cerebral hemispheres completely separate from each other, dysmorphic frontal horns, absence of falx cerebri and IHF anteriorly, mildly dysplastic genu of corpus callosum, separate basal ganglia [13] and absent septum pellucidum [11].

Syntelencephaly is postulated to result from a mutation of zic-2 gene resulting in reduction in mitotic rate and increased apoptosis in the roof plate causing non-formation of the interhemispheric fissure [9].

Patient usually presents with global developmental delay with spasticity, hypotonia or dystonia. Imaging of brain in syntelencephaly shows incomplete separation of the posterior frontal and parietal lobes [5]. The interhemispheric fissure is present anteriorly and posteriorly but it is absent in the middle [5]. In approximately 85% of cases the sylvian fissures are abnormally oriented and appear to connect with each other across the midline [13]. Grey matter heterotopia and cortical dysplasias are seen in two-thirds of syntelencephaly cases.[13] There is a variable degree of fusion seen in the bilateral thalami in patients of syntelencephaly [5]. There is partial agenesis of the corpus callosum with the formation of genu and splenium but the body is absent [13]. Syntelencephaly is the only brain malformation with such distribution of the corpus callosum. In almost all cases of syntelencephaly, an associated azygos cerebral artery is seen.[13] Many case reports of syntelencephaly have shown its association with cerebellar hypoplasia, chiari malformation, polymicrogyria and cephaloceles [9]. Most patients of syntelencephaly have normal hypothalamus, caudate and basal ganglia [13].

Differential Diagnosis List
Syntelencephaly: Middle Interhemispheric Holoprosencephaly Variant
Final Diagnosis
Syntelencephaly: Middle Interhemispheric Holoprosencephaly Variant
Case information
URL: https://www.eurorad.org/case/17438
DOI: 10.35100/eurorad/case.17438
ISSN: 1563-4086
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