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ESSENTIAL INFORMATION

Key Differential Diagnosis Issues
- Generalized seizure disorders usually nonlocalizing
- Partial complex (focal) epilepsy usually due to focal structural abnormality [i.e., focal cortical dysplasia (FCD)] - Correlate with EEG results
- High-resolution & 3T MR helpful for subtle lesions - 1-mm isotropic T1 for gray matter evaluation - 3D FLAIR imaging helpful for identifying FCD
- PET & SPECT are often complimentary to MR in identifying seizure focus prior to surgical intervention - PET: Decreased interictal metabolism in seizure focus - SPECT: Increased ictal blood flow in seizure focus
Helpful Clues for Common Diagnoses
- Idiopathic Epilepsy - No structural cause found on MR - Generalized: May be inherited - Partial: Partial motor seizures, may resolve by puberty
- Acquired Causes - Febrile seizure: Most common cause of seizure in children < 5 years - Simple febrile seizure < 15 minutes without recurrence does not require imaging - Trauma, remote stroke, or infection results in encephalomalacia &/or gliosis, which may cause epilepsy - Benign & malignant tumors - Toxic, metabolic, & drug abuse
- Vascular Malformation: Arteriovenous & cavernous malformations with hemorrhage
- Mesial Temporal Sclerosis - Most common cause of intractable temporal lobe epilepsy in adults - 2-hit hypothesis suggests initial injury with inherent vulnerability to neuronal injury - Hippocampal atrophy & gliosis - May see ipsilateral mammillary body & forniceal atrophy - Look for associated FCD, especially in the ipsilateral temporal lobe (FCD type IIIa)
- Migrational Anomalies - Focal cortical dysplasia - Newest classification Blumcke et al 2011 - Type I: Mild blurring of gray-white junction with mild increased T2 signal of subcortical white matter - More common in temporal lobes, difficult to detect - Type II: Moderate blurring of gray-white junction & increased T2 signal of subcortical white matter - Typically frontal lobes - Type IIb includes more dysmorphia & balloon cells: Highly associated with transmantle sign & easier to detect on MR - Transmantle sign: T2-hyperintense comet tail from ventricle to cortex; best seen on FLAIR - Type III: Associated with another lesion: Mesial temporal sclerosis, tumor, vascular malformation, acquired injury - Polymicrogyria - Small, pebbly, cobblestone, or micronodular-appearing gyri - Common migrational malformation with heterogeneous causes - TORCH infection (particularly CMV) is common cause of polymicrogyria & seizures - Diffuse or bilateral polymicrogyria more likely genetic/syndromic - Heterotopic gray matter - Gray matter nodules within deep white matter follow gray matter signal on all MR sequences - Subependymal most common location - Can be found incidentally in patients without seizures - Diffuse subependymal heterotopia is X-linked - Schizencephaly - Cleft extending from cortical surface to ventricular ependyma, gray matter lined - Outpouching or "dimpling" of lateral ventricular contour "points" to cleft - May be unilateral or bilateral - Open lipped: CSF in cleft; commonly bilateral - Closed lipped: No CSF with apposed walls, usually unilateral
- Septo-Optic Dysplasia Plus Syndrome - Septum pellucidum absence + optic nerve hypoplasia ± pituitary dysfunction - When SOD is associated with schizencephaly &/or polymicrogyria, it is referred to as SOD Plus
- Tuberous Sclerosis Complex - Burden of cortical dysplasias (i.e., tubers) correlates with seizure burden - T2-hyperintense cortical/subcortical tubers: Similar imaging to type IIb FCD - Cortical tubers also similar in histology to FCD type IIb with balloon cells - Subependymal nodules can enhance & calcify - 10-15% develop subependymal giant cell astrocytoma at foramen of Monro
Helpful Clues for Less Common Diagnoses
- Cortically Based Glioneuronal Tumors - Associated cortical dysplasia with tumor common (type IIIb) - Ganglioglioma - Most common cause of tumor-associated temporal lobe epilepsy - Cystic/solid cortically based mass - Ca⁺⁺ (~ 50%); enhancement (~ 50%) - Temporal lobe most common site - Dysembryoplastic neuroepithelial tumor - Discrete T2-hyperintense "bubbly" cortical mass - Medial temporal lobe most common - Enhancement may occur (~ 10%) but is less common than ganglioglioma
- Holoprosencephaly - Spectrum of failure of cleavage of midline cerebral hemispheres & telencephalon from diencephalon - Monoventricle due to absence of septum pellucidum - Complete to partial absence of other midline structures: Falx & corpus callosum - Fusion of fornices, thalami, & basal ganglia - Incomplete separation of frontal lobes - More severe cases may include large dorsal cyst
- Hemimegalencephaly - Unilateral hemispheric overgrowth - Dysplastic enlarged ipsilateral ventricle - Associated with genetic/syndromic diseases
- Sturge**-**Weber Syndrome - Unilateral trigeminal (V1 & V2) distribution facial port-wine stain - Ipsilateral malformation of cortical & pial veins = leptomeningeal enhancement - Ipsilateral enlarged choroid plexus, hemiatrophy late finding - Gyriform Ca⁺⁺ increases over time
- Status Epilepticus - Seizure > 5 minutes or > 1 seizure within 5-minute period - Higher likelihood for irreversible brain damage - 1/2 are associated with known history of epilepsy - Increased T2 signal of predominantly cortex with swelling & possible decreased diffusion
Helpful Clues for Rare Diagnoses
- Lissencephaly Type 1: Subcortical Band Heterotopia - "Smooth" brain lacking normal gyri; thick cortex - Can see subcortical smooth gray matter band in many cases - LIS1: Posterior predilection of lissencephaly - DCX (double cortex): X-linked - Females: Primarily diffuse band heterotopia - Males: Diffuse lissencephaly, more severe phenotype
- Lissencephaly Type 2 - Congenital muscular dystrophy: Walker-Warburg, Fukuyama, & muscle-eye-brain - Diffuse polymicrogyria (cobblestone lissencephaly) particularly frontal lobes & sylvian fissures - Cerebellar polymicrogyria, cysts, vermian hypoplasia, hypomyelination, & eye abnormalities can be seen
- Rasmussen Encephalitis - Likely autoimmune inflammation of unilateral cerebral hemisphere - Typically at least mesial temporal lobe & insula affected - Hemiatrophy late

References

Selected References

Images

Selected Images

Acquired Causes Coronal T2 MR in a victim of remote abusive head trauma now with seizures shows extensive areas of encephalomalacia , greater on the left. Any pathology leading to injury of the cortex puts a patient at risk for development of seizures.

Mesial Temporal Sclerosis Axial T2 MR in a patient with right mesial temporal sclerosis (not shown) demonstrates ipsilateral volume loss of right mammillary body . The medial limbic (Papez) circuit connects these structures.

Mesial Temporal Sclerosis Coronal oblique FLAIR MR in this 11-year-old patient with chronic epilepsy shows an atrophic & hyperintense left hippocampus . Careful evaluation of the more anterior left temporal lobe showed an area of focal cortical dysplasia (FCD), making this an FCD type IIIa.

Mesial Temporal Sclerosis Coronal oblique T2 MR in the same patient shows significant volume loss & loss of internal architecture of the left hippocampus . Also note the decreased size of the left fornix , often associated with mesial temporal sclerosis.

Focal Cortical Dysplasia Coronal FLAIR MR images in a 3-year-old with FCD type IIb with varying contrast windowing are shown. Note how FCD is much more conspicuous in the image on the right with windowing emphasizing greater contrast. Windowing is an important means to increasing detection of subtle FCD lesions.

Focal Cortical Dysplasia Axial T1 MR in a 4-month-old with seizures shows an area of increased signal within the frontal lobes that are not yet myelinated. FCD is most conspicuous within the first few months of life & after myelination (~ 2 years).

Polymicrogyria Parasagittal T1 MR in a 7-year-old boy with polymicrogyria shows irregularity & nodularity of the cortical surface & gray matter(GM)-white matter (WM) junction, typical of polymicrogyria.

Heterotopic Gray Matter Coronal T2 MR in a 7-year-old with seizures shows extensive subependymal GM heterotopia along the left lateral ventricular margin with overlying polymicrogyria .

Schizencephaly Coronal STIR MR shows a small, open-lipped left hemisphere cleft lined by GM with thickened gyri of pachygyria & outpouching of ventricular margin , pointing to schizencephaly. Contralateral forme fruste schizencephaly does not reach ventricular margin .

Septo-Optic Dysplasia Plus Syndrome Axial T2 MR in septo-optic dysplasia plus shows bilateral perisylvian polymicrogyria , absent septum pellucidum , & optic nerve hypoplasia. Note extensive areas of irregular cortical thickening with shallow sulci & irregular GM-WM junction.

Tuberous Sclerosis Complex Axial T2 MR shows a severe burden of hyperintense cortical dysplastic lesions (i.e., tubers) , some of which display associated dark areas of mineralization . Also note the calcified subependymal nodule along the left lateral ventricle margin.

Ganglioglioma Axial T2 MR shows a T2-hyperintense mass with indistinct margins in the left temporal lobe . Increased T2 signal of the solid component of the mass suggests a low-grade tumor.

Ganglioglioma Coronal T1 C+ FS MR shows intense & amorphous enhancement of the left medial temporal lobe mass . Gangliogliomas typically enhance, may have associated cysts, & are most likely to occur in the temporal lobe.

Dysembryoplastic Neuroepithelial Tumor Coronal T2 MR in a 10-year-old boy shows a bubbly, cystic lesion replacing the left parasagittal frontal cortex without mass effect. This is a typical appearance for a dysembryoplastic neuroepithelial tumor (DNET).

Holoprosencephaly Axial T2 MR shows severe semilobar holoprosencephaly with fused basal ganglia & frontal lobes with a large dorsal cyst communicating with monoventricle . Seizures are a symptom of this Dx.

Hemimegalencephaly Axial T2 MR in a 6-month-old girl with hemimegalencephaly (HME) shows asymmetric enlargement, cortical thickening , poor sulcation, & abnormal WM signal within the left cerebral hemisphere. Enlargement of the lateral ventricle of the affected hemisphere is common in HME.

Sturge-Weber Syndrome Axial T1 C+ MR in a young patient shows leptomeningeal angiomatosis & prominent collateral medullary venous collateral drainage, characteristic of Sturge-Weber syndrome. This vascular malformation results in poor perfusion of the cortex, chronic ischemia, & eventual neuronal death.

Sturge-Weber Syndrome Axial NECT in the same patient shows geographic cortical & subcortical calcification in areas of permanently injured brain. Calcification develops over time & is a reflection of disease severity, including severity of seizure symptoms.

Lissencephaly Type 1: Subcortical Band Heterotopia Coronal FLAIR MR shows a band of subcortical GM intensity involving the posterior frontal lobes & insula with associated pachygyria. Note T2 hyperintensity & swelling of the right hippocampal gyrus in this patient in status epilepticus.

Lissencephaly Type 1: Subcortical Band Heterotopia Axial DWI MR of a patient in status epilepticus with lissencephaly type 1 shows decreased diffusion of the hippocampal gyrus . This is potentially reversible, but does put the patient at risk for developing hippocampal sclerosis in the future.

Lissencephaly Type 1: Subcortical Band Heterotopia Axial T2 FS MR shows pachygyria with a frontal lobe predominance associated with a band of subcortical GM. This distribution is suggestive of the DCX mutation within the type 1 lissencephalies. Note the thin strip of WM in between the subcortical band & the cortex .

Lissencephaly Type 2 Axial T2 MR shows multiple cysts & bizarre architecture of the cerebellar hemispheres from cerebellar polymicrogyria. This appearance can be seen with congenital muscular dystrophies.

Lissencephaly Type 2 Axial T2 MR shows bilateral symmetric frontal polymicrogyria , yielding a cobblestone lissencephaly appearance. The type 2 lissencephalies include the dystroglycanopathies, which all have bilateral polymicrogyria as a brain malformation.

Lissencephaly Type 2 Sagittal T1 MR shows the mild brainstem hypoplasia, which can be seen with type 2 lissencephalies. Note the disorganized cerebellar polymicrogyria & frontal lobe polymicrogyria .

Rasmussen Encephalitis Coronal FLAIR shows T2 hyperintensity indicating gliosis of the cortex & subcortical WM of the insula & frontal temporal opercula with associated atrophy of the left hemisphere. This is consistent with Rasmussen encephalitis, which is thought to be an autoimmune process.

Rasmussen Encephalitis Coronal oblique FLAIR MR in an 8-year-old with chronic epilepsy shows the late hemiatrophy & signal change seen in Rasmussen encephalitis. Also note the abnormal signal within the ipsilateral hippocampus .

Additional Images

Acquired Causes Axial T1 MR shows hyperintensity related to recent hemorrhage in a cavernous malformation . Seizures are often the presenting symptom for vascular lesions, such as a cavernoma or arteriovenous malformation.

Acquired Causes Axial T2 GRE MR shows susceptibility artifact in this cavernous malformation with recent hemorrhage. GRE/SWI MR is helpful to search for additional lesions that may be occult on other sequences.*

Mesial Temporal Sclerosis Coronal FLAIR MR shows high signal in the right hippocampus related to this patient's mesial temporal sclerosis. The primary MR features are T2-hyperintense signal, atrophy of the hippocampus, & loss of internal architecture.

Mesial Temporal Sclerosis Coronal T1 MR shows the typical decreased parenchymal volume of the hippocampus in mesial temporal sclerosis. Internal architecture remains preserved in this case. Mild enlargement of the adjacent temporal horn is common.

Mesial Temporal Sclerosis Coronal FLAIR MR shows atrophy & increased signal of the right hippocampi , consistent with gliosis/sclerosis of mesial temporal sclerosis. Also note the ex vacuo dilatation of the temporal horn & asymmetric volume loss of the amygdala & parahippocampal gyrus .

Mesial Temporal Sclerosis Coronal STIR MR shows the loss of internal architecture & asymmetric atrophy of the right hippocampal gyrus . Note the ipsilateral atrophy of the right fornix .

Focal Cortical Dysplasia Coronal FLAIR MR shows a single focus of mild gyral expansion & a classic thin, high-signal seam extending to the ventricle .

Focal Cortical Dysplasia Coronal FLAIR MR shows the comet-tail transmantle sign , pointing from the cortex to the ventricle, which is indicative of a type IIb cortical dysplasia. The transmantle sign reflects radial glial migrational lines from the periventricular germinal matrix to the cortex.

Focal Cortical Dysplasia Coronal T2 MR shows classic findings in Taylor dysplasia, demonstrating juxtacortical high signal with a thin "seam" of high signal tracking along the expected course of the radial glial fibers to the subependymal margin. FLAIR is often more sensitive to these dysplasias.

Focal Cortical Dysplasia Coronal T1 MR shows thickened, ill-defined frontal cortex with mild blurring of the gray-white junctions related to focal cortical dysplasia. Such findings should be confirmed with multiplanar imaging or isovoxel reconstructions.

Focal Cortical Dysplasia Coronal T1 MR shows subtle cortical thickening & mild blurring of the gray-white junction related to focal cortical dysplasia.

Focal Cortical Dysplasia Coronal T2 MR shows an ill-defined, thickened cortex . Note the normal, thin, sharply demarcated contralateral cortex . Such findings should be confirmed with multiplanar imaging or isovoxel reconstructions to ensure no contribution from volume averaging of off axis cortex.

Heterotopic Gray Matter Axial T2 MR shows bilateral diffuse subependymal GM heterotopia . Note similar intensity with GM. These do not have enhancement or calcification commonly seen in tuberous sclerosis.

Heterotopic Gray Matter Axial T1 MR shows multifocal GM nodules lining both lateral ventricles . Note also heterotopic GM within the left frontal lobe WM . Heterotopic GM follows GM signal on all MR sequences & does not enhance.

Heterotopic Gray Matter Coronal T2 MR shows multiple foci of cortical GM lining the ependymal margin of both lateral ventricles . These may be associated with seizures or may be asymptomatic.

Schizencephaly Axial T1 MR shows a classically located perisylvian open-lip schizencephaly with a wide CSF cleft lined with GM . The cleft margins do not touch in open-lip schizencephaly.

Schizencephaly Axial T2 MR shows a closed-lip schizencephaly lined by dysplastic GM . Note the characteristic ventricular outpouching . Flow voids from embryonic vessels lay adjacent to the lateral margin of the schizencephalic cleft .

Septo-Optic Dysplasia Plus Syndrome Coronal T1 MR shows hyperintense nodule in the hypothalamus, consistent with an ectopic neurohypophysis . There is also absence of septum pellucidum . Hypoplastic optic nerves & the pituitary gland within the sella was also noted (not shown).

Schizencephaly Axial T2 MR shows an abnormal deep cleft lined with dysplastic thickened GM , extending to the ventricular margin, consistent with a closed-lip-type schizencephaly. These findings are commonly associated with septo-optic dysplasia and polymicrogyria.

Polymicrogyria Sagittal T1 MR shows small, disorganized perisylvian gyri with a cobblestone appearance, characteristic for polymicrogyria. Other areas of cortex appear thickened & indistinct related to pachygyria.

Polymicrogyria Axial T2 MR shows diffuse cortical migrational anomaly with areas of pachygyria & polymicrogyria . TORCH infections in the 1st trimester, most commonly CMV, are a common cause of nonsyndromic migrational anomalies & resulting seizures.

Polymicrogyria Axial T2 MR shows dysplastic cerebellar cortex bilaterally. This finding is often incidental & not usually associated with seizure syndromes.

Septo-Optic Dysplasia Plus Syndrome Coronal T2 MR shows septo-optic dysplasia with a small optic chiasm & absent septum pellucidum . Note that the sella is also small . These patients frequently also have pituitary hypofunction.

Septo-Optic Dysplasia Plus Syndrome Coronal T2WI MR shows right perisylvian polymicrogyria in this septo-optic dysplasia patient, a common association. However, schizencephaly is nearly always associated with polymicrogyria, adjacent to the schizencephalic cleft.

Septo-Optic Dysplasia Plus Syndrome Sagittal T1 MR shows thinning of the optic chiasm & hypoplastic appearance of the anterior pituitary , characteristic of septo-optic dysplasia. An absent septum pellucidum was also present, seen best on coronal imaging.

Tuberous Sclerosis Complex Axial T1 C+ MR shows a subependymal giant cell astrocytoma , seen in 10-15% of patients with tuberous sclerosis complex. Note the associated ventriculomegaly. Multifocal subcortical tubers are seen in the left hemisphere.

Tuberous Sclerosis Complex Coronal STIR MR shows multiple hyperintensities of the subcortical WM . With the addition of a calcified subependymal nodule , this is pathognomonic for tuberous sclerosis. Cortical tubers have a similar imaging and histological appearance with cortical dysplasia.

Tuberous Sclerosis Complex Coronal FLAIR MR shows numerous subcortical hyperintensities, consistent with tubers in this tuberous sclerosis complex patient. Several subependymal nodules are also present. Before they calcify, subependymal nodules follow WM signal.

Ganglioglioma Axial T1 C+ MR shows a circumscribed cystic WM solid mass in the anterior temporal lobe . This well-differentiated neuronal-glial tumor is the most common tumor to cause temporal lobe epilepsy.

Dysembryoplastic Neuroepithelial Tumor Axial FLAIR MR shows a tumor of the left frontal cortex with T2-hyperintense rim & heterogeneous central signal suppression . This is an exaggerated appearance of the FLAIR rim sign & microcystic variant of DNET.

Dysembryoplastic Neuroepithelial Tumor Coronal T1 MR shows a nearly cystic-appearing mass in the mesial right temporal lobe . This was a proven DNET, a neuronal tumor commonly associated with dysplastic cortex.

Hemimegalencephaly Coronal T1 MR show an enlarged right hemisphere and ventricle compared to the left. Note ipsilateral, dysplastic-appearing GM in this hemimegalencephaly patient.

Hemimegalencephaly Axial T2 MR shows diffuse enlargement of the left cerebral hemisphere with pachygyria and a dark band in the subcortical WM. Calcification can sometimes occur with cortical dysplasia. Note the ipsilateral ventricular enlargement , typical of hemimegalencephaly.

Sturge-Weber Syndrome Coronal T1 C+ MR shows right hemiatrophy, pial enhancement and angiomatosis of CSF spaces. This congenital malformation has failure of cortical venous development that leads to progressive venous occlusion and ischemia.

Sturge-Weber Syndrome Coronal T1 C+ FS MR shows ipsilateral enlarged choroid plexus glomus to the facial port-wine stain. This is associated with asymmetric pial enhancement . Hemispheric atrophy occurs late in the disease, which is not yet seen with this patient.

Sturge-Weber Syndrome Axial T1 C+ MR shows asymmetric leptomeningeal enhancement of the right temporal occipital lobe, representing abnormal pial vessels. Note the right eye proptosis from an orbital vascular malformation & an enhancing retinal angioma , also seen with Sturge-Weber syndrome.

Status Epilepticus Coronal FLAIR MR shows marked hyperintensity involving temporal cortex & adjacent subcortical WM in a patient with persistent status epilepticus. These changes resolved slowly over the following weeks.

Lissencephaly Type 1: Subcortical Band Heterotopia Axial T2 MR shows a thin band of GM in the deep WM of both hemispheres in a 6- month-old. Some consider band heterotopia to be in the GM heterotopia spectrum.

Lissencephaly Type 1: Subcortical Band Heterotopia Coronal T2 MR shows decreased sulcation, primitive sylvian fissures , & thick bands of incompletely migrated cortex consistent with band heterotopia ("double cortex"). Note that the thickness of the overlying cortex is inversely proportional to band heterotopia.

50 KiB Raw Blame History

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Helpful Clues for Common Diagnoses

Helpful Clues for Less Common Diagnoses

Helpful Clues for Rare Diagnoses