|ECR 2019 / C-1223||
|Paediatric Epilepsy Imaging - OUT --> IN approach|
Findings and procedure details
Brain CT and MR studies ordered for evaluation of seizures were evaluated from 2014 to 2018, All findings diagnosed with Out --> approach is represented with examples as follows
MRI is the modality of choice for evaluation of seizures. It is superior to CT due to its excellent inherent tissue characterization and spatial resolution.
Advanced MRI techniques spectroscopy, DTI, perfusion can also be performed.
CT brain imaging is used in the evaluation of cases of trauma or suspected tiny calcifications in MRI brain.
Functional imaging like PET/SPECT with its hybrid counterparts (CT/MRI) can be used for medically refractory seizures.
Refer figure 16 for MRI brain protocol for epilepsy.
OUT TO IN APPROACH FOR MRI BRAIN EVALUATION OF PEDIATRIC EPILEPSY:
Calvarial pathology can point to certain disease processes which can cause seizures. There can be calvarial thinning or thickening. Pathologies can be broadly categorized into focal involvement, hemispheric involvement or diffuse involvement (3).
- Refer to figures (17 and 18) for representative cases
Meningeal pathologies usually present with a headache but can also present with seizures. Meningeal involvement can be due to primary disease processes such as meningioma, meningitis, hematoma secondary to trauma, chloroma etc and can also be due to secondary involvement e.g. inflammation due to encephalitis, tumoral spread by a high-grade tumor (4).
- Refer to figures (19 and 20) for representative cases
3. ASYMMETRY OF CEREBRAL HEMISPHERES
In this approach, before specific assessment of cortex and white matter, cerebral hemispheres should be evaluated in bird's eye view for asymmetry. If when present, asymmetry should be further categorized to hemiatrophy or hemimegalencephaly (5)(6).
- Refer figures (21 and 22) for salient features of hemiatrophy and hemimegalencephaly.
- Refer figures (23 to 25) for representative cases for cerebral asymmetry.
- Refer figure (26) for an algorithmic approach for focal asymmetry.
Cortical pathologies which can cause seizures can be broadly categorized to infectious, developmental and neoplastic causes. Mesial temporal sclerosis is described as a separate entity. Cortex in the postictal state can show diffusion restriction and can mimic an ischemic stroke.
Herpes simplex (HSV) encephalitis is the most common cause of fatal sporadic fulminant necrotizing viral encephalitis. Two subtypes are recognized - neonatal herpes encephalitis, and childhood and adult herpes encephalitis (7). Childhood and adult herpes encephalitis are usually due to HSV-1 (90%) with the rest due to HSV-2 (8). In adult patients, the pattern is quite typical and manifests as bilateral asymmetrical involvement of the limbic system, medial temporal lobes, insular cortices, and inferolateral frontal lobes. The basal ganglia are typically spared, helping to distinguish it from a middle cerebral artery infarct. Extralimbic involvement is more prevalent in children, most commonly in the parietal lobe, with sparing of basal ganglia. Lesions are T1 hypointense, T2 hyperintense with diffusion restriction of the cortex (cytogenic edema) and no restriction of white matter (vasogenic edema). It may show gyral/leptomeningeal/ ring or diffuse enhancement. Blooming foci may be seen in SWI in hemorrhagic encephalitis.
- Refer figure 27 for a representative case
I) Abnormal cell proliferation disorders – cortical hamartomas of tuberous sclerosis, hemimegalencephaly, focal cortical dysplasia.
· Focal cortical dysplasia: They are one of the most common causes of epilepsy and can be associated with hippocampal sclerosis and cortical glioneuronal neoplasms. The most recent classification system is that suggested by Blumcke in 2011 and has been widely accepted (6) (9).
- Refer to figure 28
II) Abnormal neural migration disorders – Lissencephaly and heterotopia
· Lissencephaly-pachygyria spectrum includes agyria, pachygyria (broad gyri) and lissencephaly (smooth brain surface). These are again classified as type I (classic) and type II (cobblestone). In MRI, Type I (classic) lissencephaly can appear as the classic hourglass or figure-8 appearance or with a few poorly formed gyri (pachygyria) and a smooth outer surface. It is usually associated with band heterotopia. Type II lissencephaly, on the other hand, has a microlobulated surface referred to as a cobblestone complex (10).
- Refer to figure 29
III) Abnormal cortical organization
· Polymicrogyria: It is characterized by focal excessive gyrations with shallow sulci. It is often associated with schizencephaly, where is 'always' lined by polymicrogyric cortex. Predilection for the perisylvian region which is involved in 80% of patients and bilateral involvement is common (60%). In MRI, there is focal cortical thickening with increased gyrations (11).
- Refer to figure 30
· Schizencephaly: It is characterized by grey matter lined cleft extending from ependyma to pia mater. If cleft is not opposed but is separated by CSF they are open lip type, most common in bilateral cases. If well opposed they are closed lip type, common in unilateral cases. It is frequently associated (50-90%) with other cerebral anomalies such as septo-optic dysplasia, grey matter heterotopia, absent septum pellucidum (12).
- Refer to figure 31
C. Cortical Neoplasms:
- Refer to figures (32 to 34) for representative cases, imaging findings and teaching points (6).
D. Mesial temporal lobe sclerosis: Commonly referred to as hippocampal sclerosis, is the most common association with intractable temporal lobe epilepsy. Patients present with complex partial seizures (13). SPECT (Tc-99m HMPAO or ECD)9 and PET (F18-FDG) imaging are also useful adjuncts, with both ictal and interictal scans demonstrating abnormalities - ictal scan: hyperperfusion, interictal scan: hypoperfusion (13).
- Refer to figure 35 representative case.
5. GREY-WHITE MATTER JUNCTION:
In this section, the emphasis is mainly to look in islands of cortical grey matter in T1 IR, Double inversion recovery sequences.
- Refer to figures (36 to 38) for representative cases, imaging findings and teaching points (11)(12).
Many other lesions like infections (tuberculosis, NCC, toxoplasmosis), metastases etc, can involve grey and white matter junction. These are collectively described in white matter section.
6. WHITE MATTER:
Pathologies predominantly involving white matter can be congenital/developmental or acquired.
Acquired pathologies are mainly infective in etiology which presents with features of fever, headache, and seizures. Periventricular leukomalacia as sequelae to hypoxic-ischemic injury at birth. Neoplastic lesions are aggressive lesions such as glioblastoma, PNET/ATRT which presents mainly with raised ICT features (6).
- Refer figures (39 to 41) for representative cases, imaging findings and teaching points.
Congenital/developmental lesions are broadly leukodystrophies which are abnormalities due to ineffective myelination secondary to deficiency/absence of enzymes and patients present mainly with delayed or regression of milestones and seizures. Pattern-based approach with additional clues and spectroscopy findings aid to improve diagnostic accuracy for specific/differential diagnosis of leukodystrophies (14).
- Refer to figures (42 and 43) for representative cases, imaging findings and teaching points.
Abnormalities in ventricles can be of abnormal shape and size or can be of lesions within the ventricles (15) (16). Corpus callosal developmental anomalies and choroid plexus lesions are seen commonly in children presenting with seizures.
- Refer figures (44 to 47) for representative cases, imaging findings and teaching points.
Pathologies of vessels include vascular anomalies causing gliosis which subsequently acts as an epileptogenic focus (17).
Lesions such as Moya-Moya disease, unilateral ICA stenosis secondary to vasculitis by childhood viral infection, A-V malformation, Cavernoma with bleed - all these lesions can cause gliosis and cause seizures
- Refer figure (48) for a representative case.
Lesions arising in the hypothalamus can manifest with any of the following hormonal disorders: diencephalic syndrome, precocious puberty, or hormonal deficiency. Epilepsy may be the initial presenting feature in a patient with a hypothalamic lesion. Gelastic seizures (laughing fits) are a specific type of epilepsy that occurs in hypothalamic disease, especially hamartoma of the tuber cinereum (6) (18).
- Refer to figures (49) for a representative case, imaging findings and teaching points.