BRAIN CONGENITAL • Agenesis of the Corpus Callosum • Arachnoid Cyst • Craniosynostosis • Dandy-Walker Syndrome • Encephalocele • Hydrocephalus • Neurofibromatosis (NF1) • Tuberous Sclerosis
Description • A partial or complete absence of the corpus callosum.
Etiology: • Agenesis of the corpus callosum is caused by an insult that has occurred prior to the 10th week of gestation.
Epidemiology : • Anomalies (agenesis) of corpus callosum occur between 10 and 18 weeks of gestation. Males and females are equally affected.
Signs and Symptoms : • Patients may present asymptomatic; however, in many cases there are developmental abnormalities present.
Imaging Characteristics: • CT and MRI demonstrate an elevated third ventricle, noticeable separation of the lateral ventricles, partial or complete absences of the corpus callosum, and dysplasia of the cerebellum.
Treatment: • There is no treatment for this condition; however, conditions such as hydrocephalus may require treatment.
Prognosis: • Depends on other extenuating circumstances that may be related to other developmental abnormalities.
Figure 1. Agenesis of the Corpus Callosum. Coronal T2W image shows agenesis of the corpus callosum with widely spaced lateral ventricle with continuity of third ventricle with the interhemispheric fissure.
Figure 2. Agenesis of the Corpus Callosum. Axial CT (A) and axial T1W MR (B) show enlarged parallel lateral ventricles with a “race car” configuration and no corpus callosum.
Figure 3. Agenesis of the Corpus Callosum. Sagittal T1W image shows congenital absence of the corpus callosum with radially oriented gyri and the absence of the cingulategyrus.
Description • Arachnoid cysts are benign cerebrospinal fluid filled sacs which may be located in relationship to the arachnoid membrane. They do not communicate with ventricular system.
Etiology: • They are usually congenital; however, they may result from a posttraumatic or post-surgical event.
Epidemiology : • They make up about 1% of all intracranial masses. Approximately 50% to 60% occur in the middle fossa. Males are four times more likely than females to have an arachnoid cyst.
Signs and Symptoms : • Depending on the size and location of the cyst, they may go undetected. Large cysts may cause headaches, impairment of vision, seizure, increased collection of CSF, increased intracranial pressure (ICP), delay in mental and physician development, and altered behavior.
Imaging Characteristics: MRI and CT • Extraaxial benign-appearing CSF-filled cystic mass. • Most common supratentorial locations include: (1) middle cranial fossa; (2) parasellar cisterns; and (3) subarachnoid space over the convexities.
Treatment: • Surgery is used to relieve symptoms. A shunt may be used to reduce the ICP by draining the CSF into the peritoneum.
Prognosis: • Good, arachnoid cysts are benign and treatable.
Figure 1. Arachnoid Cyst.. Axial NECT shows a CSF density well circumscribed extraaxial fluid collection in the left middle cranial fossa with posterior displacement of the left temporal lobe.
Figure 2. Arachnoid Cyst.. Axial T2W (A) and T1W C+ (B) images follow the signal characteristics of the CSF.
Description • Craniosynostosis is a congenital condition in which one or more of the cranial sutures fuse prematurely. The three most common types are: (1) scaphocephaly (sagittal) the most common type; (2) plagiocephaly; and (3) trionocephaly.
Etiology: • Unknown.
Epidemiology : • Occurs in 1 out of 2,000 live births. Males are affected twice more often than females.
Signs and Symptoms : • An absence of the “soft spot” (fontanelle), a hard ridge along the affected suture, unusual head shape, or abnormal head size may be indicators for this condition. An increase in the intracranial pressure (ICP) may occur.
Imaging Characteristics: CT • Three-dimensional imaging is beneficial to see bony detail. • Bone windows show fusion of sutures. MRI • Useful for long-term follow-up.
Treatment: • Craniofacial surgery may be required.
Prognosis: • Depends on the degree of this congenital condition.
Figure 1. Craniosynostosis. Axial NECT shows elongation of the calvarium in the antero-posterior dimension and narrowing in the transverse dimension.
Figure 2. Craniosynostosis. Coronal NECT shows premature complete fusion of the sagittal suture.
Figure 3. Craniosynostosis. Lateral 3D reconstructed image (A) and above view (B) image of the skull shows complete fusion of the sagittal suture and elongation of the skull in AP dimension..
Description • Dandy-Walker Syndrome is a noncommunicating type of hydrocephalus, results from a partial dysgenesis of the vermis and a remnant fourth ventricle that communicates with a retrocerebellar cyst that is also known as a Blake pouch (see the section Hydrocephalus).
Etiology: • An atresia of the foramen of Magendie and foramina of Luschka of the fourth ventricle.
Epidemiology : • Represents approximately 2% of all cases of hydrocephalus. Occurs in 1 per 25,000 and 30,000 births and is usually diagnosed by 1 year of age. Males and females are equally affected. Associated with hydrocephalus in 80% of cases and agenesis of the corpus callosum in 20% of the cases.
Signs and Symptoms : • Related to hydrocephalus and other associated anomalies.
Imaging Characteristics: Appears as a massively dilated fourth ventricle expanding into the posterior fossa demonstrating hydrocephalus. Both CT and MRI images demonstrate a massively dilated fourth ventricle, expanded posterior fossa with an inferior hypoplasticvermis.
CT • Hypodense CSF-filled space located in the posterior fossa involving the fourth ventricle. MRI • Hypointense on T1-weighted images. • Hyperintense on T2-weighted images.
Treatment: • Surgical intervention and shunting the excess CSF into the right atrium or the peritoneum cavity.
Prognosis: • Depends on other neurologic complications; however, surgical intervention and shunting the excess CSF into the right atrium or into the peritoneal cavity will control the Dandy-Walker syndrome.
Figure 1. Dandy-Walker Syndrome. Axial NECT shows a large posterior fossa with a CSF density cyst, hypoplasticcerebellar hemispheres, and absence of the vermis.
Figure 2. Dandy-Walker Syndrome. Sagittal T1W image shows a massively dilated fourth ventricle, expanded posterior fossa, high-riding torcula, and hypoplastic cerebellum.
Figure 3. Dandy-Walker Syndrome. Axial T2W (A) and coronal T1W (B) show absence of the cerebellarvermis.
Description • Encephaloceles result form a herniation of the brain or meninges, or both, through a skull defect. The hernia may be a small CSF-filled meningeal sac or a large cyst-like structure that may exceed the size of the head. It may be covered with skin and/or membrane of varying thickness, and may contain the pons, midbrain, and vermis structures. The herniated portion of the brain is nonfunctioning.
Etiology: • Results from a congenital defect or a trauma opening in the skull.
Epidemiology : • Newborns are mostly affected. Encephaloceles account for 10% to 20% of craniospinal malformations. The incidence rate is approximately 1 to 3 per 10,000. The skull defect is commonly found in the occipital region (71%), parietal region (10%), and throughout the skull base (18%).