Journal of Dr. NTR University of Health Sciences

REVIEW ARTICLE
Year
: 2014  |  Volume : 3  |  Issue : 2  |  Page : 77--85

Congenital brain anomalies: Neuroimaging findings


Thangjam Gautam Singh1, Vaibhav Srivastav1, Pooja Singhania1, Shital Mala Devi2,  
1 Department of Radiology, Jawaharlal Nehru Medical College, Wardha, Maharashtra, India
2 Department of Pathology, RIMS, Imphal, Manipur, India

Correspondence Address:
Thangjam Gautam Singh
Department of Radiology, Jawaharlal Nehru Medical College, Wardha - 442 004, Maharashtra
India

Abstract

Congenital brain anomalies are rare among the congenital anomalies of various organ systems. It is important to diagnose these conditions at the earliest due to its far reaching neurological deficit and detrimental outcome. Most of the congenital brain anomalies can be reliably diagnose by neuroimaging (computed tomography or magnetic resonance imaging) of brain. Radiologist and treating physician should be aware of various specific imaging appearances and unique signs of these anomalies to avoid delay in diagnosis and thereby further treatment. A widely accepted classification of brain anomalies with each representative radiological image are illustrated with its distinctive findings.



How to cite this article:
Singh TG, Srivastav V, Singhania P, Devi SM. Congenital brain anomalies: Neuroimaging findings.J NTR Univ Health Sci 2014;3:77-85


How to cite this URL:
Singh TG, Srivastav V, Singhania P, Devi SM. Congenital brain anomalies: Neuroimaging findings. J NTR Univ Health Sci [serial online] 2014 [cited 2020 Mar 29 ];3:77-85
Available from: http://www.jdrntruhs.org/text.asp?2014/3/2/77/134827


Full Text

 INTRODUCTION



Central nervous system (CNS) anomalies have always fascinated radiologist with its various complicated yet unique imaging findings. Accurate identification of CNS anomalies is a prerequisite for proper management. We present here a comprehensive categorization of congenital brain anomalies with its representative examples.

 CLASSIFICATION



Congenital brain anomalies can be classified as: [1]

Disorders of primary neurulation: These are mostly neural tube closure defects and early CNS anomalies occurring during 3 rd and 4 th gestational weeks. These include Chiari malformations, cephaloceles and myelomeningoceles.Disorders of diverticulation, cleavage, sulcation and cellular migration. These include: HoloprosencephalyLissencephalyCortical dysplasiaHeterotropiaSchizencephaly.Posterior fossa malformations include: Dandy-Walker malformationsJoubert syndromeRhombencephalosynapsis.Disorder of histiogenesis

Common neurocutaneous disorders are:

Neurofibromatosis (NF)Tuberous sclerosis (TS).

Development of brain and spinal cord is referred to as dorsal induction. The basic developmental phases are divided in to: [2]

Primary neurulation: Refers to formation of brain and upper spine which occurs around 3-4 weeks gestational weeks.Secondary neurulation: Refers to formation of distal spine.

This classification was also similar to that of van der Knaap and Valk. [3]

 NEURORADIOLOGICAL FEATURES



Chiari malformations

Chiari 1

This group is characterized by herniation of "peg like" enlongated, pointed cerebellar tonsils through foramen magnum into upper cervical spinal canal [Figure 1]. Cerebellar tonsil herniation is considered abnormal if it protrudes more than 6 mm below the line joining the opisthion and basion in the first decade, 5 mm in second/third decades, 4 mm between fourth-eighth decades and 3 mm by ninth decade. [4] {Figure 1}

Computed tomography/magnetic resonance imaging (CT/MRI) will reveal the tonsillar herniation and other associated findings such as small posterior fossa, syringomyelia, atlanto-ocipital assimilation, platybasia, basilar invagination and fused cervical vertebrae. [5]

Chiari 2

These are usually accompanied by a lumbar myelomeningocele with tonsillar herniation below the foramen magnum [Figure 2]. Other findings in Chiari 2 are beaked tectum, interdigitating gyri, hydrocephalus, elongated fourth ventricle, syringohydromyelia, lacunar skull, fenestrated falx. [6] {Figure 2}

Chiari 3

In addition to the Chiari 2 malformation, this condition always comprises of high cervical and low occipital encephalocele. [7],[8],[9] Cases that do not involve the upper cervical spinal canal should not be classified as Chiari 3 malformation but they are simply as encephaloceles. [9]

Chiari 4

This include severe cerebellar hypoplasia and small brainstem and large posterior fossa cerebrospinal fluid spaces.

Two new subtle types has been added: [5]

Chiari 0

This subgroup of people are symptomatic for Chiari 1 malformations with craniocervical abnormalities of Chiari 1 malformations with arachnoid adhesions and bands with crowded foramen magnum. They have minimal or no hindbrain herniation but syringomyelia is present. It is to be due to differential cerebrospinal fluid (CSF) pressure in cervicomedullary junction. [10],[11]

Chiari 1.5.

This group comprises cases with tonsillar herniation with absence of brainstem elongation or fourth ventricle abnormalities. This was used first by Iskander and Oakes. [12]

Cephaloceles

It is protrusion of part of cranial contents through a congenital opening in cranium. The cephalocele may contain only meninges (cranial meningocele), meninges and brain tissue (encephalomeningocele or encephalocele) or meninges with brain tissue and dilated portion of ventricle (encephalocystocele or hydrencephalomeningocele or encephalomeningocystocele).

Types of cephalocele are based on its location:

Occipital cephalocele.Frontoethmoidal (sincipital) cephalocele (subtypes-nasofrontal, nasoethmoidal type naso-orbital).Cranial base cephalocele (five types: Transethmoidal [intranasal, nasopharyngeal], sphenoethmoidal, sphenopharyngeal/transsphenoidal, spheno-orbital or frontosphenoidal and sphenomaxillary.Cranial vault cephalocele (interparietal, temporal, interfrontal cephalocele).Atretic cephalocele. Cephalocele may occur in association with other malformation such as Meckel syndrome, amniotic band syndrome, trisomy 18, Dandy-Walker, Chiari, hydrocephalus, cleft lip palate, spina bifida, callosal hypoplasia.

CT/MRI may reveal the content of the herniated intracranial structures, including brain parenchyma, meninges, and cerebrospinal fluid [Figure 3]. Prognosis depends on degree of herniated brain parenchyma, which is usually gliotic and dysplastic. Rarely, ventricle can herniate.{Figure 3}

Corpus callosum anomalies

It comprises of callosal agenesis, hypoplasia and lipoma. Callosal agenesis can be complete or partial. When partial, the splenium and rostrum are always missing. In complete callosal agenesis, the entire corpus callosum as well as the cingulated gyrus and sulcus are absent [Figure 4]. Sulci and gyri on the medial hemispheric surface appear to have a radial, spoke like configuration. When partial, the splenium and rostrum are always missing.{Figure 4}

White matter axons which do not cross the corpus callosum transversely courses longitudinally and are called probst bundles, which indent and invaginate into the superomedial aspects of the lateral ventricles. The lateral ventricles are widely separated and nonconverging. They lie parallel to each other and often have small pointed frontal horns with disproportionately enlarged occipital horns (colpocephaly). The third ventricle is elevated and lies between the widely separated lateral ventricles.

Associated anomalies are absence of other commissural tracts such as anterior, hippocampal commissures, midline anomalies (interhemispheric cyst, lipomas), malformations in cortical development (heterotopias, polymicrogyria, schizencephaly etc.). [13]

Callosal lipoma

Two types are described. [14]

Tubulonodular type: Usually, bulky (>2 cm) and located at anterior part of corpus callosum and frequently associated with hypogenesis/agenesis of corpus callosum, frontal lobes anomalies, frontal encephalocele, calcifications, and/or ocular anomalies.Curvilinear type: This is ribbon like and involves posterior part [Figure 5]. They are less frequently associated with corpus callosum anomalies and/or other encephalic anomalies. [15],[16] {Figure 5}

 Disorders of Diverticulation, Cleavage, Sulcation and Cellular Migration



Holoprosencephaly

It arises due to complete or partial failure in division of developing cerebrum (prosencephalon) into hemispheres and lobes. It can be classified into three types: Alobar, semilobar and lobar holoprosencephaly. [17]

Lobar holoprosencephaly is the least severe variety. Various imaging findings squared-off frontal horns (due to absence of septum pellucidum), well-formed falx, separated/fused thalami and fusion of hemispheres in anteroinferior part only [Figure 6].{Figure 6}

Alobar variety is the most severe form and is characterized by fused ventricle (monoventricle) with "horseshoe" brain, fused thalami and basal ganglia, and absence of septum pellucidum, corpus callosum, falx cerebri and interhemispheric fissure and associated with severe craniofacial anomalies.

Holoprosencephaly may be associated with cyclops with ethmocephaly, dorsal brain cyst or olfactory nerve hypoplasia. Septum pellucidum is absent in all three forms. Extracranial anomalies such as polydactyly, renal dysplasia, omphalocele and hydrops may be associated. Myelination may be delayed.

Semilobar holoprosencephaly has variable facial anomalies like rudimentary occipital horns of lateral ventricles and partial falx.

Syntelencephaly is middle interhemispheric variant. [18] In this mild sub type of holoprosencephaly, there is midline fusion of the cerebral hemispheres between the posterior frontal and parietal lobes. The sylvian fissures on both sides are interconnected over fused brain of corpus callosum normally formed but there may be absence of body of corpus callosum. [19] Hypothalamus and lentiform nuclei normally separated. Heterotopic gray matter may be present.

Cortical dysplasia

Cortical dysplasia includes lissencephaly and nonlissencephalic cortical dysplasia. Findings on CT/MRI are diffuse or focal areas of thickened, abnormal cortex that has irregular, bumpy gyral pattern with relative decrease in underlying white matter volume.

Lissencephaly

Lissencephaly has three types. [20]

Type I: Thickened cortex, broad flat gyri, smooth grey white matter [Figure 7] interface, shallow slyvian fissure [Figure 8], colpocephaly.{Figure 7}{Figure 8}

Type II: Severe disorganized cortex, agyric, poor corticomedullary demarcation, polymicrogyric appearance.

Type III: Cerebrocerebellar type, hypoplastic cerebellum, brainstem, microcephaly, enlarged ventricles.

Focal cortical dysplasia

It is further classified (histopathologically) [21] into:

architectural dysplasiaCytoarchitectural dysplasiaTaylor's Focal cortical dysplasia (FCD): Without balloon cells,With balloon cells.

Magnetic resonance imaging findings of Taylor's FCD [22],[23],[24],[25] are:

Focal cortical thickening,blurring of the gray-white matter junction, andmarked hyperintensity of the subcortical white matter on T2-weighted images, which often appeared hypointense on T1-weighted images. In addition, the white matter signal intensity alterations often tapered toward the ventricle.

Magnetic resonance imaging findings in architectural or cytoarchitectural dysplasias (non-Taylor's FCD): [22],[23],[24],[25]

Focal brain hypoplasia, shrinkageModerate signal intensity changes in subcortical white matter (architectural dysplasia).

The lesion was generally extratemporal in Taylor's FCD and temporal in architectural dysplasia. Ipsilateral hippocampal sclerosis was often present in architectural dysplasia (dual abnormality).

Heterotopia

Grey matter heterotopias are basically normal neurons at abnormal site due to impair normal neuronal migration along radial glial fibers. [26] It can be periventricular, subcortical and laminar.

Periventricular (subependymal) heterotopias

These are nodular grey matter foci in subependymal area which shows signal intensity similar to cortex on all MR sequences and doesnot enhance [Figure 8].

Subcortical heterotopias

They can be nodular, curvilinear or mixed in morphology and are usually seen within the subcortical or deep white matter. The overlying cortex may be thinned with shallow sulci. Nodular subcortical heterotopias (SCH) appear as nodules or larger mass like lesion that extend from the ventricular surface outward into the white matter without continuity with the cerebral cortex. Curvilinear SCH appears as heterogeneous curvilinear masses of gray matter that extends from the cortical surface into the white matter. Blood vessels, CSF may be seen within the layer of the gray matter.

Laminar heterotopias

It is the extra neuronal bands in between cortex and ventricles, which on MRI appears as continuous double cortex with the cortex and bilateral symmetric circumferential subcortical layer of band heterotopia separated from each other by a thin white matter band. The cortex may be relatively normal or pachygyric. [27],[28],[29],[30]

Schizencephaly

Cerebrospinal fluid cleft lined by grey matter. It extends from ependymal area to pia surfaces.

Two types:

Open type: Cleft walls in apposition [Figure 9]Closed type: Cleft walls far apart [Figure 10].{Figure 9}{Figure 10}

 POSTERIOR FOSSA MALFORMATIONS



Dandy-Walker malformation [31] is characterized by enlarged posterior fossa with cystic dilatation of fourth ventricle and upward displacement of transverse sinuses, tentorium and torcular herophili (lambdoid-torcular inversion) associated with varying degree of vermian aplasia or hypoplasia [Figure 11].{Figure 11}

Dandy-Walker variant

Mild vermian hypoplasia (VH) with variable sized cystic space caused by communication of posteroinferior fourth ventricle and cistern magna through an enlarged vallecula (key hole appearance).

Joubert syndrome

The most important component Joubert syndrome [32] is the dysgenetic vermis which may appear split or segmented. The inferior and superior cerebellar peduncles are often small and fourth ventricular roof appears superiorly convex giving the classical "molar tooth" appearances on CNS imaging [Figure 12]. Other morphologic features include: Dysgenesis of the isthmic portion of the brain stem at the pontomesencephalic junction, and sagittal vermic clefting.{Figure 12}

Associated supratentorial findings include hippocampal malrotation, callosal dysgenesis, migration disorders, cephaloceles, and ventriculomegaly.

The term Joubert syndrome and related disorder (JSRD) refers to all conditions having molar tooth sign (MTS). MTS and VH causing distortion and enlargement of the fourth ventricle [33],[34],[35] are mandatory diagnostic criteria as they are the most consistent finding in JSRD.

The "Joubert-plus anomaly" [34] comprises the Joubert malformation plus additional anomalies of the mesencephalon or fourth ventricle;

Rhombencephalosynapsis

It comprises of agenesis of vermis leading to midline fusion of the cerebellar hemispheres, peduncles and fusion of dentate nuclei and variable fusion of colliculi [Figure 13]. [36] {Figure 13}

In partial rhombencephalosynapsis, [37] there is normal anterior vermis and nodulus with absent posterior vermis and partial fusion of the inferior part of the cerebellar hemispheres.

 DISORDER OF HISTIOGENESIS



Tuberous sclerosis

The classic clinical triad consists of papular facial nevus, seizure and mental retardation. CNS manifestation includes cortical tubers, white matter lesions, subependymal nodules (along lateral ventricles along striothalamic groove) [Figure 14] and subependymal giant cell astrocytoma (located in foramen of monro). [38] Non-CNS lesions are renal angiomyolipoma, cardiac rhabdomyomas, hepatic leiomyomas, hepatic, pancreatic adenomas, shagreen patches, subungual fibromas and facial angofibromas.{Figure 14}

The diagnostic criteria is modified from those of Roach et al.: [39]

Definitive TS complex: Either 2 major features or 1 major and 2 minorProbable TS complex: 1 major and 1 minorPossible TS complex: Either 1 major or 2 or more minor.

Major features

Facial angiofibroma or forehead plaqueNontraumatic ungual or periungual fibromaHypomelanotic macules (3 or more)Shagreen patchMultiple retinal nodular hamartomasCortical tuberSubependymal noduleSubependymal giant cell astrocytomaCardiac rhabdomyomaLymphangiomyomatosisRenal angiomyolipoma.

Minor features

Dental pits: Multiple and randomly distributedRectal polyps: HamartomatousBone cystsCerebral white matter migration linesGingival fibromasNonrenal hamartomaRetinal achromic patch"Confetti" skin lesionsMultiple renal cysts.

Tubers typically appear as areas of increased signal intensity in the cortical and subcortical regions on T2-weighted and fluid attenuated inversion recovery MRI. It enhances in 3-4 % of cases. [40]

Subependymal nodules are located along the walls of lateral ventricle. It may enhance rarely.

Subependymal giant cell astrocytoma. [40] It usually arises near the foramen of monro leading to obstruction and hydrocephalus. It appears has heterogeneous signal intensity on T1- and T2-weighted sequences. It enhances heterogeneously on postcontrast study.

Neurofibromatosis

These are heterogeneous group of diseases included in neurocutaneous syndrome/phakomatoses. Two main types:

Neurofibromatosis Type I: (Von Recklinghausen disease)

Diagnostic criteria: 2 or more of following findings: [41]

6 or more 5 mm or larger café-au-lait spots1 plexiform neurofibroma or 2 or more neurofibromas of any type [Figure 15]2 or more lisch nodulesAxillary/inguinal region frecklingOptic nerve gliomaFirst degree relative with NF1Bone lesion - Dysplasia of greater wing of sphenoid, pseudoarthrosis.{Figure 15}

Neurofibromatosis Type II

The criteria for definite diagnoses of neurofibromatosis Type II [42] are as follows

Bilateral CN VIII schwannomas [Figure 16]. On MRI or CT scan (no biopsy necessary)First-degree relative with NF2 and either unilateral early-onset CN VIII schwannoma (age <30 year) or any two of the following: MeningiomaGliomaSchwannomaJuvenile posterior subcapsular lenticular opacity (juvenile cortical cataract).{Figure 16}

Presumptive diagnoses of neurofibromatosis Type II

Early onset of unilateral CN VIII schwannomas on MRI or CT scan detected in patients younger than 30 years and one of the following: MeningiomaGliomaSchwannomaJuvenile posterior subcapsular lenticular opacity.Multiple meningiomas (>2) and unilateral CN VIII schwannoma or one of the following: GliomaSchwannomaJuvenile posterior subcapsular lenticular opacity.

 CONCLUSION



Identification of distinctive neuroimaging findings of various congenital brain anomalies are immensely helpful in diagnosing the anomalies and further management.

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