giving me fits: improved detection of subtle abnormalities in epilepsy elliott friedman and maria...

Giving Me Fits: Improved Detection of Subtle Abnormalities in Epilepsy

Elliott Friedman and Maria Olga Patino

eEdE-07

No disclosures

Objectives• To improve accuracy of MRI interpretation in patients with epilepsy,

focusing on subtle epileptogenic lesions and MRI protocol optimization.

• All of the imaging cases in this presentation contain abnormalities that were not fully appreciated at the time of initial imaging interpretation.

• We will focus on these imaging pitfalls to improve diagnosis of epileptogenic lesions, allowing radiologists to generate more accurate and useful imaging reports, improving patient care.

Introduction

• Epilepsy is the fourth most common neurologic disorder in the United States and Europe. One in 26 people will develop epilepsy during their lifetime.

• Eligibility for resections of neocortical focal epilepsies are highly dependent on the identification of a lesion on imaging.

• Detection of an epileptogenic lesion on MRI improves the prognosis for long-term seizure freedom after epilepsy surgery.

• The most common reasons that detectable epileptogenic lesions are underreported on MRI is because the imaging does not adequately delineate the lesion, or an incomplete search pattern of the interpreting radiologist.

Case 1 Case 2 Case 3 Case 6Case 5Case 4

1.5 T v 3 T

1.5 T3 T


1.5 T v 3 T

T1-weighted 3 Tesla images more clearly depict the bilateral occipital supependymal heterotopia (arrows), which is inconspicuous on the 1.5 Tesla scan.


1.5 T v 3 T

1.5 T 3 T


1.5 T v 3 T

1.5 T 3 T

Extensive right hemispheric polymicrogyria which is more clearly delineated on the 3T scan.


1.5 T v 3 T

• When patient safety allows, epilepsy imaging should be performed on a 3 Tesla scanner.

• Improved signal to noise ratio of 3T MRI provides better resolution and image quality, and has been shown to more effectively detect and characterize structural lesions.


1.5 T v 3 T

• Image quality on 1.5T scanners can vary by scanner and technique.

• Both sets of T1-weighted images were obtained on 1.5T scanners, but gray-white distinction is not perceptible on the images to the left, and these images are not sufficient to evaluate for cortical abnormalities.


High resolution T1 sequence

T2 T1



T2 3D T1



Diffuse posterior laminar heterotopia (arrows) is only conspicuous on the 3D T1 gradient echo sequence (MPRAGE, 3D SPGR) which optimizes contrast between the gray and white matter.



Fig. 1 Fig. 2

Compare the resolution of the heterotopia on the 3D T1 sequence (Fig. 2) with the T1 SE sequence (Fig. 1) performed as part of the same

study.

• High resolution 3D T1-weighted gradient echo sequence (MPRAGE, SPGR) optimizes T1 contrast and signal to noise ratio, providing high spatial resolution.

• Improves sensitivity for detection and delineation of white matter heterotopias and dysplasias.



T2 Flair

3D T1

Right frontal parasagittal focal cortical dysplasia (arrows). The 3D T1-weighted sequence more clearly delineates the subcortical extent of abnormality.


Sagittal flair cube sequence

Axial and coronal T2 Flair



Sagittal volumetric T2 Flair

The volumetric sagittal flair cube sequence demonstrates hyperintense subcortical signal wrapping around the affected gyrus and radiating to the lateral ventricle, which was much less conspicuous on the

routine axial and coronal T2 sequences. Pathologically proven Type IIB Focal cortical dysplasia



Coronal T2 Flair

Axial T2 Flair



Sagittal Flair cube

The bottom of sulcus dysplasia is obvious on the sagittal 3D flair sequence but less

conspicuous on the routine axial and coronal T2 flair sequences (arrows next

slide).



Coronal T2 Flair

Axial T2 Flair



• A volumetric sagittal T2 Flair (1 mm isotropic voxels) or a sagittal double inversion recovery sequence more clearly demonstrate some subtle focal cortical dysplasias, such as bottom of sulcus dysplasias.

• Bottom of sulcus dysplasias are important cortical developmental malformations to recognize because these lesions can be highly epileptogenic and prognosis for seizure freedom is excellent after resection; however they are often subtle on routine imaging due to their location and small size.

• Imaging features of bottom of sulcus dysplasia include: cortical thickening, gray-white matter blurring, and increased T2 signal in the subcortical white matter and cortex centered at the bottom of a sulcus, sometimes with associated gyral abnormality and sulcal widening, and a funnel-shaped tail of signal extending towards the ependymal surface.


Subtle cortical abnormalities

Axial and coronal T2 Flair



FDG PET obtained one hour following a seizure demonstrates focal increased activity in the left posterior insular cortex (arrow).

Review of T2 Flair images with narrow

windows (upper images) is critical to detect subtle white

matter abnormalities. Arrows point to a

subtle focus of subcortical T2 hyperintensity,

pathologically proven type IIA Focal Cortical

dysplasia.



Coronal T2

Axial T2

Coronal T2 Flair

Subtle focus of hypointense signal in the left temporal opercular cortex (yellow

arrows) and subtle focus of subcortical T2 hyperintensity (blue arrow). Pathology

revelealed meningiomatosis and cortical dysplasia in the superior temporal gyrus.

Anterior temporal lobe changes


Axial T2



Coronal T2



FDG PET

Anterior temporal lobe white matter changes include: anterior temporal lobe volume loss, increased T2 signal intensity in the white matter core, and loss of gray-white distinction. FDG PET

demonstrates diffusely decreased activity in the left anterior temporal lobe (blue arrows).



• Morphologic changes of the anterior temporal lobe occur in persons with intractable temporal lobe epilepsy with or without hippocampal sclerosis.

• Frequently overlooked finding on MRI.

• Increased T2 signal in the white matter core in association with anterior temporal lobe atrophy.

• Signal changes may reflect increased water content, possibly due to myelin abnormality, but not believed to be related to gliosis.

Meningoencephalocele


Left middle cranial fossa meningoencephalocele (yellow arrows).

Asymmetric decreased size and blurring in the left hippocampus, pathologically

proven Ammon’s horn sclerosis.



Multiple small meningoencephaloceles in the

left middle cranial fossa (arrows)



• Many epilepsy protocols only include high resolution coronal images through the hippocampal formations.

• This effectively excludes the anterior aspect of the middle cranial fossa, a common location for encephaloceles.

63 yo woman with a 5 year history of medically refractory seizures, initially attributed to a prior stroke.

Initial image from the coronal oblique sequence of a prior MRI, interpreted as negative, because the abnormality was outside of the field of view.



Axial and coronal T2-weighted images obtained approximately one year later using a volumetric sequence through the whole brain clearly demonstrate the transalar meningoencephalocele and associated dysplastic brain.

High resolution coronal or coronal oblique T2-weighted imaging must be acquired through the whole brain as part of any epilepsy protocol.

Conclusions• You CANNOT report what you CANNOT see.

• Effective imaging evaluation of epilepsy requires a dedicated epilepsy protocol MRI optimized for detection of subtle lesions as well as an awareness of commonly overlooked lesions.

• Meticulous inspection and narrow display windows improve detection of subtle lesions.

• Detecting the epileptogenic lesion improves the prognosis for long-term seizure freedom after epilepsy surgery.

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Hesdorffer DC, Logroscino G, Benn EK, et al. Estimating risk for developing epilepsy. A population-based study in Rochester, Minnesota. Neurol 2011; 76:23-27.

Hofman PA, Fitt GJ, Harvey AS, et al. Bottom-of-sulcus Dysplasia: Imaging Features. AJR 2011; 196: 881-885.

Mitchell LA, Jackson GD, et al. Anterior temporal lobe abnormality in temporal lobe epilepsy: a quantitative MRI and histopathologic study. Neurol 1999; 52:327-336.

Phal P, Usmanov A, Nesbit G, et al. Quantitiative comparison of 3T and 1.5T MRI in evaluation of epilepsy. AJR. 2008; 191: 890-895.

Tellez-Zenteno J, Ronquillo L, Moein-Afshari F, et al. Surgical outcomes in lesional and non-lesional epilepsy: A systematic review and meta-analysis. Epil Res. 2010; 89: 310-318.

giving me fits: improved detection of subtle abnormalities in epilepsy elliott friedman and maria...

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