Differential Diagnoses, Summaries, and Imaging Pitfalls

FETAL VENTRICULOMEGALY

Isolated Mild Unilateral Ventriculomegaly Brain structurally normal Good prognosis	Isolated Bilateral Ventriculomegaly Brain structurally normal Often mild Good prognosis	Porencephaly CSF-filled cavity Communicates (usually) with ventricle Ischemia and infection most common causes
Hemorrhage Variety of maternal and fetal etiologies May cause hydrocephalus	Aqueductal Stenosis Variety of acquired (hemorrhage, infection) and malformative etiologies Severe ventriculomegaly, including the third with normal fourth ventricle Ventricular diverticula Enlarged head circumference	Dandy-Walker Malformation Hypoplastic and rotated vermis Fourth ventricle enlarged Large posterior fossa Hydrocephalus
Chiari 2 Malformation Small posterior fossa with crowding (“banana sign”) Hindbrain herniation Small head circumference “Lemon”-shaped calvarium Hydrocephalus Myelomeningocele	TORCH Infection Parenchymal calcification Volume loss and ventriculomegaly +/- malformations	Callosal Dysgenesis/Agenesis May be isolated or occur with other malformations Colpocephalic ventriculomegaly Severe ventriculomegaly with coexisting aqueductal obstruction

NEONATAL ENCEPHALOPATHY

Hypoxic Ischemic Injury Variable pattern based on mild, moderate (watershed) versus severe insult (central gray or diffuse) Image at 3 to 5 days post insult	Hypoglycemia Posterior predilection Symmetric restricted diffusion in acute phase Atrophy in chronic phase	Metabolic Disorders Disorders presenting in the neonatal period and mimicking hypoxic ischemic injury (HII) include urea cycle disorders, nonketotic hyperglycinemia, maple syrup urine, and sulfite oxidase.
Meningoencephalitis Group B strep and Escherichia coli most common causes in neonates Leptomeningeal enhancement Purulent debris in the subarachnoid space and ventricles Cerebritis/central and peripheral infarcts Subdural empyema	Dural Venous Sinus Thrombosis Etiology most commonly from dehydration or coagulopathy Peripheral, central, or combined venous Parenchymal venous edema, infarct, and/or hemorrhage	Arterial Stroke Variety of fetal and maternal causes (e.g., coagulopathy, arteriopathy, thromboembolic, etc.); often idiopathic Entire or partial singular or multiple arterial territories Middle cerebral artery distribution most common

HYPOXIC ISCHEMIC INJURY SEVERITY PATTERN ON MRI

HEAD ULTRASOUND FINDINGS

Hydrocephalus Disproportionate enlargement of the ventricles relative to the sulci	Germinal Matrix Hemorrhage Hyperechoic material at caudalthalmic groove	Periventricular Venous Hemorrhagic Infarct Complication of prematurity that results in a parenchymal hemorrhage
Intraventricular Hemorrhage Hyperechoic intraventricular material and hyperechogenic ependymal lining	Subdural Hemorrhage Often seen with abusive head trauma and coagulopathy	Meningitis Expanded hyperechoic subarachnoid spaces

HEAD ULTRASOUND FINDINGS

Stroke Wedge-shaped region of loss of gray-white matter differentiation Challenging diagnosis on ultrasound	Hypoxic Ischemic Injury Effaced sulci and poor gray-white matter differentiation	Subpial and Parenchymal Hemorrhage Hyperechoic region within the parenchyma and adjacent extra-axial space
Vein of Galen Aneurysmal Malformation Hypoechoic structure in the pineal region with arterial and venous flow	Callosal Malformation Common brain malformation	Simplified Gyral Pattern Undersulcation of the brain with respect to age

ABNORMAL CORTEX

Classical Lissencephaly Agyria-pachygyria (broad thickened cortex); may be complete (diffuse) or incomplete with anteroposterior gradient	Simplified Gyral Pattern Diffuse undergyration of the brain parenchyma	Schizencephaly Dysplastic gray matter lined open or closed CSF-filled clefts
Polymicrogyria Excessive number of abnormally small gyri and sulci; may be unilateral or bilateral	Pachygyria Thickened cortex with broad gyri	Heterotopia Anomalously located gray matter, which can be subependymal, subcortical, or transmantle

ABNORMAL CORTEX

Hemimegalencephaly Enlarged dysplastic hemisphere with enlarged ventricle Can partially affect the cerebral hemisphere Can be isolated or syndromic	Stenogyria Apparent increase in number of gyri due to collapse of normal gyri without dysplasia Associated with Chiari 2 malformation		Ulegyria Ischemic cortical insult to the brain that preferentially involves the cortex within the depth of sulcus, creating “mushroom-shaped” gyri
Cobblestone Lissencephaly Thickened cortex with nodules of gray matter deep to the cortex associated with congenital muscular dystrophies such as Walker-Warburg		Band Heterotopia Band of gray matter deep to the cortex separated by subcortical white matter. Shallow sulci and ventriculomegaly may coexist.

ABNORMAL CORPUS CALLOSUM

Callosal Agenesis Malformation resulting in complete absence of the corpus callosum.	Callosal Hypogenesis and Dysgenesis Malformation resulting in incomplete (hypogenesis) or partial dysplastic (dysgenesis) formation of the corpus callosum.	Callosal Agenesis with Interhemispheric Cyst Coexisting interhemispheric cysts may or may not communicate with the ventricle.
Holoprosencephaly Semilobar and lobar holoprosencephaly demonstrates greater posterior than anterior formation of the corpus callosum.	Callosal Lipoma Globular or curvilinear lipomas demonstrate T1W hyperintensity.	Callosal Thinning and Defects Callosal thinning and callosal defects can be secondary to white matter volume loss and injury due to HII, hemorrhage, or surgery.

HOLOPROSENCEPHALY SPECTRUM

Alobar	Semilobar	Lobar

ASYMMERTRIC SIZE OF CEREBRAL HEMISPHERES

Encephalomalacia Old infarcts, trauma, and infections can result in encephalomalacia.	Hemimegalencephaly Hamartomatous overgrowth of a part or entire cerebral hemisphere characteristically demonstrating polymicrogyria and ipsilateral enlarged lateral ventricle.Caused by PIK3/Akt/mTOR pathway mutations.			Rasmussen Encephalitis Refractory epilepsy caused by a viral, autoimmune, or inflammatory process. Progressive atrophy and subcortical T2 hyperintensity of a cerebral hemisphere. Typically involves the temporal, frontal, and insular lobes.
Porencephaly Prematurity-related periventricular hemorrhagic ischemia can result in focal parenchymal destruction and ventricular expansion, resulting in asymmetry. Following shunting, the brain will often collapse internally and become asymmetrically smaller.			Sturge-Weber Chronic venous ischemia results in progressive parenchymal volume loss and cortical dystrophic calcification. Calvarial hypertrophy and paranasal sinus expansion. Enlarged ipsilateral choroid plexus. Glaucoma.

INTRACRANIAL CYST

Arachnoid Cyst Arachnoid-lined extra axial CSF-filled cyst following simple fluid signal on all sequences most commonly found in the middle cranial fossa	Epidermoid Cyst Ectoderm derived extra axial lesions with diffusion restriction	Colloid Cyst Anterior superior third ventricle cyst with variable signal intensity/density that may cause acute hydrocephalus
Rathke Cyst Congenital cyst centered in the sella	Pineal Cyst Usually an incidental finding. Follow-up imaging can be recommended if larger than 1 cm or wall thickening greater than 1–2 mm	Choroidal Fissure Cyst Simple cyst in the medial temporal lobe above the fimbria/alveus

INTRACRANIAL CYST

Neurenteric Cyst Cyst anterior to the pontomedullary junction Variable signal based on protein content	Choroid Plexus Cyst Simple cyst of choroid plexus typically not of clinical significance but can be seen with trisomies	Neuroepithelial Cyst Also known as neuroglial cyst; congenital epithelial lined and can occur anywhere Typically simple fluid signal
Cystic Periventricular Leukomalacia Irregular cystic spaces in periventricular white matter due to parenchymal insult in premature patients	Germinolytic Cyst Congenital or acquired (e.g., posthemorrhagic) cyst(s) centered in the germinal matrix Classically seen with CMV infection and Zellweger syndrome	Connatal Cyst Normal variant small cysts superior and lateral to frontal horns

POSTERIOR FOSSA CYSTS

Differential Diagnosis of Posterior Fossa Cysts.
Malformation	Vermis	Fourth Ventricle	Posterior Fossa	Hydrocephalus	Occipital Scalloping
Dandy-Walker Malformation	Hypoplastic, markedly rotated	Enlarged	Enlarged	Frequent	Yes
Inferior Vermian Hypogenesis	Inferior portion hypoplastic, and rotated to a lesser extent than Dandy-Walker	Enlarged	Normal or slightly enlarged	Usually absent	No
Blake Pouch Cyst	Normal, slightly upwardly rotated usually less than vermian hypoplasia	Often enlarged	Normal or slightly enlarged	Variable depending on whether the cyst perforates	Possible
Arachnoid Cyst	Normal, occasionally compressed, not rotated	Normal or reduced	Normal or slightly enlarged	Rare	Yes
Mega Cisterna Magna	Normal and not rotated	Normal or slightly enlarged	Normal	Absent	No

LOW CEREBELLAR TONSILS

• Pachymeningeal enhancement

• Enlarged pituitary

• Distended dural sinuses

• Subdural fluid collections

• Decreased mamillopontine distance

• Papilledema

• Empty Sella

• Optic nerve tortuosity

• Optic nerve sheath dilatation

• Slit-like ventricles

• Transverse sinus compression

• Small posterior fossa.

• Chiari 2 has associated myelomeningocele.

• Effaced sulci and cisterns

• Multiple causes: Hydrocephalus, cerebral edema, mass effect, meningitis, and trauma

DISORDERS WITH CEREBELLAR DYSPLASIA, HYPOPLASIA, OR ATROPHY

• 1

  Prematurity—Germinal matrix hemorrhage can lead to symmetric or asymmetric hypoplasia.

• 2

  Tubulinopathy—Malformation of basal ganglia.

• 3

  PHACES—Hemangioma, arterial abnormality.

• 4

  Tuberous sclerosis.

• 1

  Neuronal ceroid lipofucinosis

• 2

  Spinocerebellar ataxia

• 3

  Congenital glycosylation disorder

• 4

  Infantile neuroaxonal dystrophy

• 5

  Ataxia telangiectasia

• 6

  Medication toxicity

• 1

  Alpha-dystroglycanopathies (e.g., Walker-Warburg)—Supratentorial cortical malformation similar to PMG, brainstem kinking, muscle and eye involved

• 2

  GPR56 & COL3A1—Bifrontal PMG

• 3

  Poretti-Bolthauser (LAMA1)—Retinal abnormality

• Bilateral cerebellar germinal matrixhemorrhage

• 1

  CASK—Simplified gyral pattern

• 2

  VLDLR & Reelin-pachygyria/lissencephaly

• 3

  Chudley-McCullough/GPSM2—Partial agenesis of corpus callosum, frontal PMG, heterotopia

DTI BRAIN MALFORMATIONS ¹

1 DTI data in this section were postprocessed by using DTIStudio software (Johns Hopkins University, Baltimore, Maryland).

DTI BRAIN MALFORMATIONS

DTI BRAIN MALFORMATIONS

DTI BRAIN MALFORMATIONS

CONGENITAL INFECTIONS “TORCHeZ”

• Scattered intracranial Ca ²⁺

• Chorioretinitis and microphthalmia

• Ventriculomegaly

• Migration anomalies not a feature

BACTERIAL MENINGITIS IMAGING FINDINGS

EPILEPTOGENIC LESIONS

• Sessile or pedunculated; large or small masses of the hypothalamus

• Follows gray matter signal on all sequences

• Heterogeneous T2W hypointense/T1W hyperintense

• Susceptibility with hemosiderin ring

• Associated with developmental venous anomaly in ~25% of patients

A wide variety of cortical malformations, including polymicrogyria, heteroropia, lissencephaly, hemimegalencephaly, etc., may cause epilepsy.

Focal cortical dysplasia (FCD) type I, II and III.

Cortical insults of any etiology may eventually cause epilepsy, including from prior infection or infarct.

• T2W hyperintensity, volume loss, and loss of internal architecture

• May be unilateral or bilateral

• Ipsilateral volume loss of the fornix and mamillary body can be seen

• Can occur in conjunction with cortical dysplasia

Progressive hemispheric volume loss typically involving frontal, temporal and insular lobes with T2 signal abnormality

STATUS EPILEPTICUS FINDINGS

PATTERNS OF DYSPLASIAS

ETIOLOGY OF INTRAPARENCHYMAL HEMORRHAGE

• Parenchymal contusions commonly frontal and temporal

• Diffuse axonal injury commonly found in the corpus callosum, subcortical white matter and less commonly the basal ganglia and brainstem

• Infection

• Fluid/electrolyte imbalance

• Autoimmune disorders

• Prothrombotic factor (e.g., protein C and S, factor V Leiden, etc.)

• L-asparaginase medication

• AVM

• AV fistula

• Cavernoma