Epilepsy, General

Bronwyn E. Hamilton, MD

DIFFERENTIAL DIAGNOSIS

Common

Acquired Causes
- Trauma
- Remote Stroke
- Remote Infection
- Neoplasms
- Mesial Temporal Sclerosis (MTS)
- Vascular Malformations
- Toxic/Metabolic Insult, NOS
- Drug Abuse
Heterotopic Gray Matter
Perisylvian Dysplasia
Schizencephaly
Septo-Optic Dysplasia
Tuberous Sclerosis Complex (TSC)
Focal Cortical Dysplasia, Taylor Type (Balloon Cell Dysplasia)
Focal Cortical Dysplasia
Pachygyria-Polymicrogyria
Lissencephaly Type 1
Band Heterotopia
Hemimegalencephaly

Less Common

Neuronal & Mixed Neuronal-Glial Tumors
- DNET
- Ganglioglioma
Pleomorphic Xanthoastrocytoma

Rare but Important

Sturge-Weber Syndrome
Status Epilepticus

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Generalized seizure disorders usually nonlocalizing
Partial complex (focal) epilepsy usually due to focal structural abnormality (i.e., MTS)
High-resolution MR necessary to fully evaluate epilepsy

Helpful Clues for Common Diagnoses

Acquired Causes
- Trauma is most common cause in adults
- Trauma, remote stroke, or infection results in encephalomalacia &/or gliosis, which may cause epilepsy
- Benign, malignant tumors
- MTS: Small, hyperintense hippocampus associated with temporal lobe epilepsy
- Causative vascular malformations include AVM & cavernous malformations
- Toxic-metabolic & drug abuse patients may present with seizures
Heterotopic Gray Matter
- Gray matter (GM) nodules, follow GM signal on all MR sequences
- Subependymal most common location
- Can be found incidentally in patients without seizures
Perisylvian Dysplasia
- Common site for cortical dysplasia
- Typically bilateral
- ± Septo-optic dysplasia, schizencephaly
Schizencephaly
- CSF cleft extending to ventricular ependyma, GM-lined
- Outpouching or “dimpling” of lateral ventricular contour “points” to cleft
- Two morphologic varieties
  - Closed lip: GM ependymal seams touch
  - Open lip: GM seams separated by cleft
- May be unilateral or bilateral
- Absent septum pellucidum common
- Associated with septo-optic dysplasia
Septo-Optic Dysplasia
- Some consider mildest form of holoprosencephaly
- Septum pellucidum absence + optic nerve hypoplasia, ± pituitary dysfunction
- Common associated malformations: Schizencephaly, perisylvian dysplasia
Tuberous Sclerosis Complex (TSC)
- T2 hyperintense cortical/subcortical tubers
- Subependymal nodules follow white matter (WM) signal until calcified
- 10-15% develop giant cell astrocytoma
Focal Cortical Dysplasia, Taylor Type (Balloon Cell Dysplasia)
- Imaging & histology = tubers in TSC
  - Histology shows “balloon cell” dysplasia
- Solitary dysplasia; lack other TSC features
- T2 hyperintense “comet tail” from cortex to ventricle; best seen on FLAIR > T2 > T1
Focal Cortical Dysplasia
- Thickening &/or nodular cortex
- Blurred gray-white junction
Pachygyria-Polymicrogyria
- Pachygyria: Thick, smooth cortex
- Polymicrogyria: Small, “pebbly”, cobblestone or micronodular appearing gyri (cortical dysplasia)
Lissencephaly Type 1
- “Smooth” brain lacking normal gyral infolding; thick cortex
- Spectral continuum with polymicrogyria-pachygyria
Band Heterotopia
- Most genetic; X-linked inheritance
- Most (90%) are female
  - Males severely affected, rare survival
- Band of incompletely migrated GM between cortex & ventricle (double cortex)
- GM band size inversely proportional to overlying cortex thickness
Hemimegalencephaly
- Unilateral hemispheric overgrowth
- Dysplastic enlarged ipsilateral ventricle
- Overlying skull & soft tissues overgrown

Helpful Clues for Less Common Diagnoses

DNET
- Discrete T2 hyperintense “bubbly” cortical mass, low grade neuronal neoplasm
- Associated cortical dysplasia common
- Medial temporal lobe most common
Ganglioglioma
- Cystic/solid enhancing, cortically based mass, mixed neuronal-glial tumor
- Temporal lobe most common site
- Associated cortical dysplasia common
Pleomorphic Xanthoastrocytoma
- Cyst + enhancing nodule classic
- Well-circumscribed, no surrounding edema
- Involvement of adjacent meninges typical

Helpful Clues for Rare Diagnoses

Sturge-Weber Syndrome
- Malformation of cortical & pial veins
- Clinical diagnosis by trigeminal distribution facial “port-wine” stain
- Earliest intracranial finding = ipsilateral enlarged choroid plexus
- Later = ipsilateral hemiatrophy
Status Epilepticus
- Focal cortical (& subcortical) edema, T2 hyperintense
  - Varied cortical enhancement
  - Usually DWI & FLAIR bright
- Persistent seizures, often > 24 hours
- May show hyperperfusion: High CBV & CBF, delayed MTT
- Most resolve in days-weeks
- Long term atrophy may result

Other Essential Information

“New onset seizures” require routine brain MR with & without contrast
- Rule out acute lesions: Hemorrhage, tumor, infection, & stroke
“Epilepsy” high resolution MR evaluation
- High resolution T1/T2 (3D techniques at 1 mm slices preferred) through entire brain
- IR techniques improve gray-white matter contrast (STIR, FLAIR, & T1 FLAIR)
- High field strength (3T) preferred

Image Gallery

Coronal FLAIR MR shows high signal in the right hippocampus

related to this patient’s MTS. The primary MR features are T2 hyperintense signal, atrophy of the hippocampus, & loss of internal architecture.

Coronal T1WI MR shows typical decreased parenchymal volume

of the hippocampus in MTS. Internal architecture remains preserved in this case. Mild enlargement of the adjacent temporal horn is common.

(Left) Axial T1WI 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 AVM. (Right) Axial T2* GRE MR shows susceptibility artifact in this cavernous malformation