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Neuroradiology Case of the Week
Case 418
June 2009
Gurshawn Singh, MS2, and
Virendra Kumar, MD
Clinical
Presentation: Patient is a newborn with occipital encephalocele.
Imaging Findings: This patient presented with a dysplastic brain, tonsillar herniation, a dysplastic corpus callosum with a notched clivus. The sac which holds the dysplastic brain and is filled with blood is visible on the T1 sagittal view. The T2 sagittal allows viewing of the large massa intermedia. The T1W FLAIR shows heterotopia along the lateral margin of the right lateral ventricle. This encephalocele was protruding through a defect in the occipital bone. On Axial CT, herniation of the brain parenchyma through the occipital bone is visible.
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| Figure 1: T1 sagittal view shows encephalocele with dysplastic brain, tonsillar herniation,dysplastic corpus callosum, and notched clivus.
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Figure 2: T2-weighted sagittal view shows large massa intermedia, and encephalocele with dysplastic brain.
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Figure 3: T1W Flair view shows encephalocele, and heterotopia along the lateral margin of right lateral ventricle.
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| Figure 4: Bony defect in occipital bone with herniation of brain parenchyma. |
Diagnosis: Encephalocele
Discussion: Encephalocele is a neural tube defect which are among the most common congenital anomalies next to cardiac defects. Encephalocele is herniation of the brain/meninges through a skull defect.
Neural tube defects arise from embryological defects as the neural plate which elevates and fuses to form the neural tube, will actually have delayed fusion of the anterior neural tube in encephalocele. This results in a large neural pore forming an open communication between the lumen of the neural tube and the amniotic cavity. Brain parenchyma ends up protruding through the bony defects of the skull. It most commonly occurs on the posterior skull through occipital bone and less commonly in the nasofrontal area creating an encephalocele. This along with Chiari II is also referred to as a Chiari III malformation.
There are multiple intracranial anomalies associated with encephalocele. Chiari malformations, holoprosencephaly, Dandy-Walker complex, aqueduct stenosis, agenesis of the corpus callosum, and other midline abnormalities are associated with encephaloceles, so those must be taken into consideration also if there is a patient with encephalocele.
These embryological defects can occur because of genetic factors, folic acid deficiency during pregnancy, metabolic disorders, and several disruptive factors of pregnancy. Folic acid deficiency is common in pregnant women and is one of the primary causes of neural tube defects because it is necessary in de novo DNA synthesis. Thus, with folate deficiency, DNA synthesis and transcription of genes for neurulation may be defective or impaired, resulting in incomplete neurulation, and thus, encephalocele.
Encephaloceles present as herniations of the skull where the brain hangs out of the skull in a sac of skin. The brain within the sac is usually disorganized and not fully formed. Encephaloceles are most often diagnosed clinically, with the most severe lesions occurring prior to 26 days after conception. Complete CNS imaging is important since 15-20% of children have additional severe CNS defects. The calvarial defects can be seen radiographically and CT can be useful as it may give us information on what are the contents of the encephalocele. However the MRI is best diagnostic modality to look for complete extent, contents and additional anomaly associated with encephalocele.
References:
- van der Put NM, van Straaten HW, Trijbels FJ, Blom HJ. Folate, homocysteine and neural tube defects: an overview. Exp Biol Med (Maywood). 2001 Apr;226(4):243-70. [PubMed]
- Abdullah NNL. Case of the Month: Occipital Encephalocoele. Radiology Malaysia. http://www.radiologymalaysia.org/Content/2006/MedPro/CaseReports/2004/11/29110402.html
- Osborn AG. Diagnostic Imaging: Brain. Amirsys, 2004.
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