- Email: [email protected]
Pediatric Seizure Imaging
Pediatric Seizure Imaging Savas Tepe, MD,a Raymond W. Sze, MD,b and Nadja Kadom, MDb
The objective of this article was to show the spectrum of magnetic resonance and computed tomographic abnormalities in the pediatric seizure patient. Seizure is a common indication for pediatric neuroimaging. Characteristic imaging findings can lead to a specific pathologic diagnosis. Imaging findings may be subtle. Clinical correlation and optimization of magnetic resonance imaging protocols are important for seizure imaging.
The incidence of seizures in the United States pediatric population is 0.5 to 1%. Fifteen to 30% of these patients have disease refractory to medical therapy and may benefit from surgery.1 Computed tomography (CT) and magnetic resonance imaging (MRI) are used for localization and characterization of epileptogenic foci, functional evaluation, prognosis, and follow-up after either medical or surgical treatment. CT is useful for identifying acute hemorrhage and for calcification, which can be present in tumors, intracranial infections, and certain phakomatoses. Magnetic resonance (MR) is superior to CT for detection of cortical and subcortical epileptogenic foci and abnormalities of gray and white matter development. Not all causes of epilepsy require MR or CT imaging. Febrile convulsions, hypoxia, metabolic and electrolyte imbalance, and hypoglycemia are common causes of seizure requiring treatment of the underlying cause rather than imaging with MR or CT.1
MRI Technique Our seizure protocol includes sagittal T1; axial T1, T2, fluid attenuated inversion recovery (FLAIR); coronal T2, and thin-section T1-weighted inversion recovery; From the aDepartment of Radiology, University of Arizona, Tucson Arizona, and bDepartment of Pediatric Radiology, Children’s National Medical Center, Washington, DC. Reprint requests: M. Savas Tepe, MD, Department of Radiology, University of Arizona, 1501 N Campbell Avenue, Tucson AZ 85724. E-mail: [email protected]. Curr Probl Diagn Radiol 2007;36:237-46. © 2007 Mosby, Inc. All rights reserved. 0363-0188/2007/$32.00 ⫹ 0 doi:10.1067/j.cpradiol.2007.04.002
Curr Probl Diagn Radiol, November/December 2007
and T2-weighted inversion recovery through the hippocampi. The coronal slices are invaluable for assessing hippocampal symmetry and signal intensity; they should be obtained perpendicular to the long axis of the hippocampus. A good internal reference to assess positioning is symmetry of the internal auditory canals and labyrinthine structures. Gadolinium is rarely used for seizure imaging unless a concern for neoplasm is raised during the examination.
Developmental Anomalies Gray Matter Heterotopias Gray matter (GM) heterotopias are collections of nerve cells in abnormal locations secondary to arrest of radial migration of neurons. Arrested neurons may be found anywhere along the migrational path from the periventricular germinal zone to the cortex. Risk factors include maternal trauma, infection, or exposure to toxins.2 Subependymal heterotopia are the most common type of heterotopias and are frequently multiple1,3 (Fig 1A). Subcortical GM heterotopia (Fig 1B-C) can appear mass-like and multinodular and may exert mass effect on the adjacent ventricle. Heterotopia follows normal gray matter signal on all sequences and does not enhance.2,4,5 Band heterotopic manifests as stripes of GM situated between the lateral ventricles and the cerebral cortex; multiple bands are separated from each other by a layer of normal-appearing WM (Fig 1D-E).
Lissencephaly and Lissencephaly Complex Lissencephaly is the most severe abnormality of neuronal migration and is characterized by a smooth, agyric cortex (Fig 2). Many patients with band heterotopia have significantly reduced number of sulci and gyri and may actually be better classified as having incomplete lissencephaly, which is more common than the complete form.6
237
FIG 1. (A) Four-year-old male with subependymal heterotopia. Axial T2-weighted image through the atria of the lateral ventricles demonstrate subependymal, linear, nodular, mass-like lesions (arrows) causing indentation of lateral ventricle at the level of central temporal region bilaterally. The lesions are isointense to gray matter (GM) on all sequences. The patient presented with partial seizures. (B and C) Five-year old female child with a small focus of subcortical GM heterotopia (arrow). Coronal (B) and axial T2W (C) images demonstrate subcortical, focal, nodular, curvilinear lesion in subcortical white matter (WM) of the posterior left frontal lobe following GM signal intensity. This patient was followed up clinically for 4 years and was seizure free. (C) Axial T2. (D and E) Three-year-old girl with band heterotopia complex. (D) Axial T2W image through the lateral ventricle frontal horns. (E) Left parasagittal T1W. Diffuse continuous abnormal signal intensity throughout both cerebral hemispheric cortex in the temporal region as well as similar abnormalities in the right periventricular regions, particularly at the posterior regions of the ventricular horns. Lesions match GM signal; findings are consistent with broad band bilateral periventricular heterotopic GM. The abnormal signal region is separated from the cortex by a thin layer of normal-appearing white matter, giving the impression of a double cortex. There is no focal heterotopia. The patient presented with partial seizures and developmental delay in motor and social skills
238
Curr Probl Diagn Radiol, November/December 2007
FIG 2. Eleven-year-old female, Lissencephaly complex. Axial T1W image through the lateral ventricles shows thick cortex with a few flat and broad gyri, adjacent WM layer and thick band of heterotopia configuration paralleling throughout the supratentorial cortex. Heterotopic GM is separated from the thinned cortex by a thin layer of white matter (arrows). Note the smooth appearance of the brain, absent sulci in the temporal and occipital lobes. Frontoparietal lobes are undersulcated.
FIG 4. Two-year-old boy with unilateral schizencephaly. Axial T2W MRI demonstrates that unilateral CSF cleft in the posterior left frontal lobe lined by irregular, thickened cortical mantle isointense to GM. Superior aspect of the cleft extends from the pial surface to the ependyma of the left lateral ventricle; the margins of the inferior portion of the cleft are apposed. Gyri and sulci radiate into cleft and GM lines the cleft. This case is mixed opened and closed lip type. Note, dimple (arrow) in the wall of the lateral ventricle where the cleft communicates is helpful for differential diagnosis from porencephaly. Heterotopia, deep infoldings of polymicrogyria, and tubers sometimes could be confused with this diagnosis. Schizencephaly is usually unilateral but bilaterality is not infrequent.6 The patient has partial complex seizures, right motor hemiparesis, and developmental delay.
FIG 3. Sixteen-year-old girl with focal cortical dysplasia of Taylor. Coronal T2W image from midbrain and posterior fossa demonstrate that an abnormal focus of hyperintensity involves the left posterior temporal lobe cortex and underlying subcortical WM, expanding the gyri, with blurring of the cortical–WM junction and marked T2 prolongation of the underlying WM (arrow). The lesion did not enhance with gadolinium. The patient suffers from autism, complicated by generalized tonic clonic epilepsy for years.
Curr Probl Diagn Radiol, November/December 2007
239
FIG 5. (A) Three-month-old infant with a hamartoma of TS. Nonenhanced CT image shows slightly hyperdense mass lesion in subcortical right frontal lobe, displacing the right lateral ventricle frontal horn (arrow). Lesion showed no contrast enhancement. The patient has new onset partial seizure. (B) Gadolinium-enhanced T1W image, another example of TS. Multiple subependymal calcified and noncalcified (arrows) nodules and cortical tubers in this 2-year-old patient with complex partial seizures. Subependymal nodules are more typical for TS and imaging appearance differs with age; they rarely calcify in the first year of age.1 (C) Mixed low and high T1 signal become high on this T2W axial plane sequence, most consistent with cortical diffuse supratentorial subcortical tubers (arrows). There was no convincing evidence of enhancement. Areas of small cysts/perivascular space enlargement common in tuberous sclerosis with unknown clinical significance.
Focal Cortical (Taylor) Dysplasia This is considered a forme fruste of the tuberous sclerosis (TS) complex, because the cortical hamartomas of patients with TS are histologically and radiologically identical6 (Fig 3). The histology of the cerebral cortex is disturbed; abnormal cells in the cerebral cortex and in the underlying hypertrophied WM include large, dysplastic neurons, gliosis, and balloon cells, admixed with normal neurons.
Schizencephaly Schizencephaly is a frequently bilateral congenital malformation characterized by GM-lined transmantle clefts that extend through the entire hemisphere, from the ependymal lining of the lateral ventricles to the pial covering of the cortex.4 Etiologies include mutations or early prenatal insult affecting the germinal zone before neuronal migration4,6 (Fig 4).
Tuberous Sclerosis FIG 6. Nine-year-old boy with mesial temporal sclerosis on the left. Coronal T2W image. Hyperintense signal, asymetry, atrophy, and loss of internal architecture of the left hippocampus (arrow), related to neuronal loss and gliosis. Secondary signs of MTS include enlarged ipsilateral temporal horn of lateral ventricle, and mamillary body atrophy.
240
Among the common phakomatoses, TS usually involves multiorgan hamartomas including CNS; all contain giant balloon cells and various neoplasms are common.1,3 The white matter lesions lie along the
Curr Probl Diagn Radiol, November/December 2007
FIG 7. (A) Five-year-old boy with acute lymphocytic leukemia and fever presents for evaluation of new onset seizure and focal neurologic deficit. Noncontrast head CT images at two different levels demonstrate ring-shaped calcifications (arrow) with surrounding edema in right frontal lobe, near vertex in GM-WM junction. Patient had neurocycticercosis. (B) Axial T1W with gadolinium. Different patient, 7-year-old boy. Subcortical, ring-enhancing lesion in right peripheral parietal lobe seen in this axial T1W post-gadolinium-enhanced image (arrow). The lesion demonstrates fluid signal characteristics. (C) Axial T2W image shows surrounding vasogenic edema (arrow). (D) Axial FLAIR sequence nicely demonstrates, but T2W image obscured, hyperintense foci of an eccentric, diagnostic scolex (arrow, rounded cyst with dot inside). Calcification narrows the differential diagnosis and makes septic emboli unlikely. Endemic regions change the order of differential diagnosis.
Curr Probl Diagn Radiol, November/December 2007
241
FIG 8. (A) Tuberculosis. Eleven-month-old male. Multiple brain lesions are hyperdense on noncontrast CT. (B) Axial T2W. MRI shows surrounding edema. (C) Solid enhancement of the lesions detected on T1W postgadolinum coronal image (arrows) (C).
242
Curr Probl Diagn Radiol, November/December 2007
oratory findings help differentiate neurocysticercosis from other neurological infections (Fig 8).
Rasmussen Encephalitis This chronic, progressive, focal encephalitis usually begins in childhood and is refractory to antiepileptic medications. The cause is unknown; proposed etiologies include viral triggers, genetic predisposition, and immune dysfunction. Parenchymal injury occurs with microglial nodules and perivascular T-cell lymphocytic infiltration, followed by cortical swelling, and eventually, atrophy. Frontal and temporal lobe involvement is most common7 (Fig 9).
Tumors Ganglioglioma
FIG 9. Nine-year-old male child with violent behavior and frequent suspension from school with partial motor seizures and nocturnal enuresis. Spine MR was normal. Unilateral, diffuse right hemispheric volume loss, atrophy (arrows), with subtle high signal abnormality in gray and white matter of temporal lobe and in hippocampus demonstrated in this coronal T2W image (right hemispheric GM-WM interface is less distinct compared with the left). Biopsy from the pathologic samples revealed parenchymal injury with microglial nodules and perivascular T-cell lymphocytic infiltration; atrophy, consistent with diagnosis of Rasmussen encephalitis.
This well-differentiated, slowly growing neuroepithelial tumor composed of neoplastic glial cells is the most common tumor causing temporal lobe epilepsy.3,6 Although they can occur anywhere, the most common location is in the superficial temporal lobe. Malignant transformation is rare6 (Fig 10).
lines of neuronal migration.3 Subependymal hamartomas differ histologically from the cortical hamartomas; those located near the foramen of Monro tend to cause hydrocephalus3 (Fig 5).
This is a well-defined, nonneoplastic congenital mass (this may be considered a heterotopia) of GM located in the region between the mamillary bodies and the tuber cinereum of the hypothalamus. It is characterized clinically by central precocious puberty and/or gelastic seizures3,6,8 (Fig 11).
Mesial Temporal Sclerosis (MTS) MTS is the most common cause of partial complex seizures in children and volume loss of the hippocampus is characteristic3,4 (Fig 6). MTS may be acquired (neonatal, perinatal event) or developmental.4 MTS is bilateral in 20% of cases and cortical dysplasia is the most common dual pathology with MTS cases.2
Hypothalamic (Tuber cinereum) Hamartoma
Vascular Malformations Arteriovenous malformation and cavernous malformations can cause seizures and occur in up to 70% of patients with vascular malformations6,8 (Figs 12 and 13).
Conclusion Infectious and Inflammatory Neurocycticercosis Neurocycticercosis is a parasitic infection secondary to Taenia solium. The parenchymal form is the most common; lesions are usually multiple and may be at different stages in the same patient4,5 (Fig 7). Imaging characteristics, clinical presentation, and lab-
Curr Probl Diagn Radiol, November/December 2007
Imaging abnormalities in the pediatric seizure patient range from obvious masses to very subtle GM heterotopias. Calcification is better evaluated by CT. MR is much more sensitive for detecting areas of cortical dysplasia or ectopic GM. Close clinical correlation, optimized MRI protocol (including careful head positioning within the coil), and a systematic approach to interpretation is critical.
243
FIG 10. (A) Two-year-old female patient with ganglioglioma suffers from repetitive temporal lobe partial complex epilepsy. Coronal T2W image demonstrates a superficial, discrete cystic and solid temporal lobe mass expanding the overlying cortex without significant surrounding vasogenic edema (arrow). (B) Axial T1W postgadolinium image of the same patient demonstrates intense enhancement of the mural nodule (arrow), with mild displacement of amygdala inferiorly.
FIG 11. Four-year-old boy with gelastic seizures. Axial FLAIR (A) and sagittal T1 (B) show a round, nonenhancing mass (arrow), contiguous with tuber cinereum within the hypothalamus. Mass is isointense on T1 and slightly hyperintense on T2. There was no enhancement after gadolinium administration. This patient’s gelastic seizures were refractory to medical therapy for 2 years. (B) Sagittal T1.
244
Curr Probl Diagn Radiol, November/December 2007
FIG 12. Seven-year-old girl patient with arteriovenous malformation (AVM). (A) Contrast-enhanced CT shows partially enhancing right frontoparietal mass that could represent a slow growing tumor or AVM. (B) Axial T2W MRI demonstrates hypointense signal intensity hemosiderin rim around the predominantly hyperintense mass, a vascular malformation. The mass contains signal voids which may represent vascular flow void or calcification. CT showed that they were not calcified. The presence of compact collections of vascular tangle connecting feeding arteries to prominent draining veins without an intervening capillary network helps establish a diagnosis of AVM.
FIG 13. Seventeen-year-old male with cavernous malformation. (A) Hallmark of cavernous malformation is the popcorn appearance on MR with a T2 dark rim, and a T2 bright center (arrow). (B) Coronal GRE sequence shows blooming (arrow). (C) Axial noncontrast CT demonstrates hyperdense heterogeneous lesion on the right frontal convexity, not as diagnostic as MRI.
Curr Probl Diagn Radiol, November/December 2007
245
REFERENCES 1. Ball WS. A clinical approach to imaging in childhood epilepsy. Pediatric Neuroradiology, Jr. New York: Lippincott-Raven, Chapter 12. p. 489-504. 2. Melhem ER, Hoon AH, Ferrucci JT, et al. Periventricular leukomalacia: Relationship between lateral ventricular volume on brain MRI and severity of cognitive and motor impairment. Radiology 2000;214:199-204. 3. Bronen RA, Fulbright RK, Kim JH, et al. A systematic approach for interpreting MR images of the seizure patient. AJR 1997;169:241-7.
246
4. Bradley WG, Shey R. How do I do it? MR imaging evaluation of seizures. Radiology 2000;214:651-6. 5. Wyllie E, Comair Y, Kotagal P, et al. Seizure outcome after epilepsy surgery in children and adolescents. Ann Neurol 1998;44:740-8. 6. Dobyns WB, Truwit CL. Lissencephaly and other malformations of cortical development. Neuropediatrics 1995;26:132-47. 7. Bien CG, Granata T, Antozzi C, et al. Pathogenesis, diagnosis and treatment of Rasmussssen encephalitis. A European consensus statement. Brain 2005;128:454-71. 8. Urbach H, Hattingen J, Von Oertzen J, et al. MRI in the presurgical work up of patients with drug resistant epilepsy. AJNR 2004;25:919-26.
Curr Probl Diagn Radiol, November/December 2007
The objective of this article was to show the spectrum of magnetic resonance and computed tomographic abnormalities in the pediatric seizure patient. Seizure is a common indication for pediatric neuroimaging. Characteristic imaging findings can lead to a specific pathologic diagnosis. Imaging findings may be subtle. Clinical correlation and optimization of magnetic resonance imaging protocols are important for seizure imaging.
The incidence of seizures in the United States pediatric population is 0.5 to 1%. Fifteen to 30% of these patients have disease refractory to medical therapy and may benefit from surgery.1 Computed tomography (CT) and magnetic resonance imaging (MRI) are used for localization and characterization of epileptogenic foci, functional evaluation, prognosis, and follow-up after either medical or surgical treatment. CT is useful for identifying acute hemorrhage and for calcification, which can be present in tumors, intracranial infections, and certain phakomatoses. Magnetic resonance (MR) is superior to CT for detection of cortical and subcortical epileptogenic foci and abnormalities of gray and white matter development. Not all causes of epilepsy require MR or CT imaging. Febrile convulsions, hypoxia, metabolic and electrolyte imbalance, and hypoglycemia are common causes of seizure requiring treatment of the underlying cause rather than imaging with MR or CT.1
MRI Technique Our seizure protocol includes sagittal T1; axial T1, T2, fluid attenuated inversion recovery (FLAIR); coronal T2, and thin-section T1-weighted inversion recovery; From the aDepartment of Radiology, University of Arizona, Tucson Arizona, and bDepartment of Pediatric Radiology, Children’s National Medical Center, Washington, DC. Reprint requests: M. Savas Tepe, MD, Department of Radiology, University of Arizona, 1501 N Campbell Avenue, Tucson AZ 85724. E-mail: [email protected]. Curr Probl Diagn Radiol 2007;36:237-46. © 2007 Mosby, Inc. All rights reserved. 0363-0188/2007/$32.00 ⫹ 0 doi:10.1067/j.cpradiol.2007.04.002
Curr Probl Diagn Radiol, November/December 2007
and T2-weighted inversion recovery through the hippocampi. The coronal slices are invaluable for assessing hippocampal symmetry and signal intensity; they should be obtained perpendicular to the long axis of the hippocampus. A good internal reference to assess positioning is symmetry of the internal auditory canals and labyrinthine structures. Gadolinium is rarely used for seizure imaging unless a concern for neoplasm is raised during the examination.
Developmental Anomalies Gray Matter Heterotopias Gray matter (GM) heterotopias are collections of nerve cells in abnormal locations secondary to arrest of radial migration of neurons. Arrested neurons may be found anywhere along the migrational path from the periventricular germinal zone to the cortex. Risk factors include maternal trauma, infection, or exposure to toxins.2 Subependymal heterotopia are the most common type of heterotopias and are frequently multiple1,3 (Fig 1A). Subcortical GM heterotopia (Fig 1B-C) can appear mass-like and multinodular and may exert mass effect on the adjacent ventricle. Heterotopia follows normal gray matter signal on all sequences and does not enhance.2,4,5 Band heterotopic manifests as stripes of GM situated between the lateral ventricles and the cerebral cortex; multiple bands are separated from each other by a layer of normal-appearing WM (Fig 1D-E).
Lissencephaly and Lissencephaly Complex Lissencephaly is the most severe abnormality of neuronal migration and is characterized by a smooth, agyric cortex (Fig 2). Many patients with band heterotopia have significantly reduced number of sulci and gyri and may actually be better classified as having incomplete lissencephaly, which is more common than the complete form.6
237
FIG 1. (A) Four-year-old male with subependymal heterotopia. Axial T2-weighted image through the atria of the lateral ventricles demonstrate subependymal, linear, nodular, mass-like lesions (arrows) causing indentation of lateral ventricle at the level of central temporal region bilaterally. The lesions are isointense to gray matter (GM) on all sequences. The patient presented with partial seizures. (B and C) Five-year old female child with a small focus of subcortical GM heterotopia (arrow). Coronal (B) and axial T2W (C) images demonstrate subcortical, focal, nodular, curvilinear lesion in subcortical white matter (WM) of the posterior left frontal lobe following GM signal intensity. This patient was followed up clinically for 4 years and was seizure free. (C) Axial T2. (D and E) Three-year-old girl with band heterotopia complex. (D) Axial T2W image through the lateral ventricle frontal horns. (E) Left parasagittal T1W. Diffuse continuous abnormal signal intensity throughout both cerebral hemispheric cortex in the temporal region as well as similar abnormalities in the right periventricular regions, particularly at the posterior regions of the ventricular horns. Lesions match GM signal; findings are consistent with broad band bilateral periventricular heterotopic GM. The abnormal signal region is separated from the cortex by a thin layer of normal-appearing white matter, giving the impression of a double cortex. There is no focal heterotopia. The patient presented with partial seizures and developmental delay in motor and social skills
238
Curr Probl Diagn Radiol, November/December 2007
FIG 2. Eleven-year-old female, Lissencephaly complex. Axial T1W image through the lateral ventricles shows thick cortex with a few flat and broad gyri, adjacent WM layer and thick band of heterotopia configuration paralleling throughout the supratentorial cortex. Heterotopic GM is separated from the thinned cortex by a thin layer of white matter (arrows). Note the smooth appearance of the brain, absent sulci in the temporal and occipital lobes. Frontoparietal lobes are undersulcated.
FIG 4. Two-year-old boy with unilateral schizencephaly. Axial T2W MRI demonstrates that unilateral CSF cleft in the posterior left frontal lobe lined by irregular, thickened cortical mantle isointense to GM. Superior aspect of the cleft extends from the pial surface to the ependyma of the left lateral ventricle; the margins of the inferior portion of the cleft are apposed. Gyri and sulci radiate into cleft and GM lines the cleft. This case is mixed opened and closed lip type. Note, dimple (arrow) in the wall of the lateral ventricle where the cleft communicates is helpful for differential diagnosis from porencephaly. Heterotopia, deep infoldings of polymicrogyria, and tubers sometimes could be confused with this diagnosis. Schizencephaly is usually unilateral but bilaterality is not infrequent.6 The patient has partial complex seizures, right motor hemiparesis, and developmental delay.
FIG 3. Sixteen-year-old girl with focal cortical dysplasia of Taylor. Coronal T2W image from midbrain and posterior fossa demonstrate that an abnormal focus of hyperintensity involves the left posterior temporal lobe cortex and underlying subcortical WM, expanding the gyri, with blurring of the cortical–WM junction and marked T2 prolongation of the underlying WM (arrow). The lesion did not enhance with gadolinium. The patient suffers from autism, complicated by generalized tonic clonic epilepsy for years.
Curr Probl Diagn Radiol, November/December 2007
239
FIG 5. (A) Three-month-old infant with a hamartoma of TS. Nonenhanced CT image shows slightly hyperdense mass lesion in subcortical right frontal lobe, displacing the right lateral ventricle frontal horn (arrow). Lesion showed no contrast enhancement. The patient has new onset partial seizure. (B) Gadolinium-enhanced T1W image, another example of TS. Multiple subependymal calcified and noncalcified (arrows) nodules and cortical tubers in this 2-year-old patient with complex partial seizures. Subependymal nodules are more typical for TS and imaging appearance differs with age; they rarely calcify in the first year of age.1 (C) Mixed low and high T1 signal become high on this T2W axial plane sequence, most consistent with cortical diffuse supratentorial subcortical tubers (arrows). There was no convincing evidence of enhancement. Areas of small cysts/perivascular space enlargement common in tuberous sclerosis with unknown clinical significance.
Focal Cortical (Taylor) Dysplasia This is considered a forme fruste of the tuberous sclerosis (TS) complex, because the cortical hamartomas of patients with TS are histologically and radiologically identical6 (Fig 3). The histology of the cerebral cortex is disturbed; abnormal cells in the cerebral cortex and in the underlying hypertrophied WM include large, dysplastic neurons, gliosis, and balloon cells, admixed with normal neurons.
Schizencephaly Schizencephaly is a frequently bilateral congenital malformation characterized by GM-lined transmantle clefts that extend through the entire hemisphere, from the ependymal lining of the lateral ventricles to the pial covering of the cortex.4 Etiologies include mutations or early prenatal insult affecting the germinal zone before neuronal migration4,6 (Fig 4).
Tuberous Sclerosis FIG 6. Nine-year-old boy with mesial temporal sclerosis on the left. Coronal T2W image. Hyperintense signal, asymetry, atrophy, and loss of internal architecture of the left hippocampus (arrow), related to neuronal loss and gliosis. Secondary signs of MTS include enlarged ipsilateral temporal horn of lateral ventricle, and mamillary body atrophy.
240
Among the common phakomatoses, TS usually involves multiorgan hamartomas including CNS; all contain giant balloon cells and various neoplasms are common.1,3 The white matter lesions lie along the
Curr Probl Diagn Radiol, November/December 2007
FIG 7. (A) Five-year-old boy with acute lymphocytic leukemia and fever presents for evaluation of new onset seizure and focal neurologic deficit. Noncontrast head CT images at two different levels demonstrate ring-shaped calcifications (arrow) with surrounding edema in right frontal lobe, near vertex in GM-WM junction. Patient had neurocycticercosis. (B) Axial T1W with gadolinium. Different patient, 7-year-old boy. Subcortical, ring-enhancing lesion in right peripheral parietal lobe seen in this axial T1W post-gadolinium-enhanced image (arrow). The lesion demonstrates fluid signal characteristics. (C) Axial T2W image shows surrounding vasogenic edema (arrow). (D) Axial FLAIR sequence nicely demonstrates, but T2W image obscured, hyperintense foci of an eccentric, diagnostic scolex (arrow, rounded cyst with dot inside). Calcification narrows the differential diagnosis and makes septic emboli unlikely. Endemic regions change the order of differential diagnosis.
Curr Probl Diagn Radiol, November/December 2007
241
FIG 8. (A) Tuberculosis. Eleven-month-old male. Multiple brain lesions are hyperdense on noncontrast CT. (B) Axial T2W. MRI shows surrounding edema. (C) Solid enhancement of the lesions detected on T1W postgadolinum coronal image (arrows) (C).
242
Curr Probl Diagn Radiol, November/December 2007
oratory findings help differentiate neurocysticercosis from other neurological infections (Fig 8).
Rasmussen Encephalitis This chronic, progressive, focal encephalitis usually begins in childhood and is refractory to antiepileptic medications. The cause is unknown; proposed etiologies include viral triggers, genetic predisposition, and immune dysfunction. Parenchymal injury occurs with microglial nodules and perivascular T-cell lymphocytic infiltration, followed by cortical swelling, and eventually, atrophy. Frontal and temporal lobe involvement is most common7 (Fig 9).
Tumors Ganglioglioma
FIG 9. Nine-year-old male child with violent behavior and frequent suspension from school with partial motor seizures and nocturnal enuresis. Spine MR was normal. Unilateral, diffuse right hemispheric volume loss, atrophy (arrows), with subtle high signal abnormality in gray and white matter of temporal lobe and in hippocampus demonstrated in this coronal T2W image (right hemispheric GM-WM interface is less distinct compared with the left). Biopsy from the pathologic samples revealed parenchymal injury with microglial nodules and perivascular T-cell lymphocytic infiltration; atrophy, consistent with diagnosis of Rasmussen encephalitis.
This well-differentiated, slowly growing neuroepithelial tumor composed of neoplastic glial cells is the most common tumor causing temporal lobe epilepsy.3,6 Although they can occur anywhere, the most common location is in the superficial temporal lobe. Malignant transformation is rare6 (Fig 10).
lines of neuronal migration.3 Subependymal hamartomas differ histologically from the cortical hamartomas; those located near the foramen of Monro tend to cause hydrocephalus3 (Fig 5).
This is a well-defined, nonneoplastic congenital mass (this may be considered a heterotopia) of GM located in the region between the mamillary bodies and the tuber cinereum of the hypothalamus. It is characterized clinically by central precocious puberty and/or gelastic seizures3,6,8 (Fig 11).
Mesial Temporal Sclerosis (MTS) MTS is the most common cause of partial complex seizures in children and volume loss of the hippocampus is characteristic3,4 (Fig 6). MTS may be acquired (neonatal, perinatal event) or developmental.4 MTS is bilateral in 20% of cases and cortical dysplasia is the most common dual pathology with MTS cases.2
Hypothalamic (Tuber cinereum) Hamartoma
Vascular Malformations Arteriovenous malformation and cavernous malformations can cause seizures and occur in up to 70% of patients with vascular malformations6,8 (Figs 12 and 13).
Conclusion Infectious and Inflammatory Neurocycticercosis Neurocycticercosis is a parasitic infection secondary to Taenia solium. The parenchymal form is the most common; lesions are usually multiple and may be at different stages in the same patient4,5 (Fig 7). Imaging characteristics, clinical presentation, and lab-
Curr Probl Diagn Radiol, November/December 2007
Imaging abnormalities in the pediatric seizure patient range from obvious masses to very subtle GM heterotopias. Calcification is better evaluated by CT. MR is much more sensitive for detecting areas of cortical dysplasia or ectopic GM. Close clinical correlation, optimized MRI protocol (including careful head positioning within the coil), and a systematic approach to interpretation is critical.
243
FIG 10. (A) Two-year-old female patient with ganglioglioma suffers from repetitive temporal lobe partial complex epilepsy. Coronal T2W image demonstrates a superficial, discrete cystic and solid temporal lobe mass expanding the overlying cortex without significant surrounding vasogenic edema (arrow). (B) Axial T1W postgadolinium image of the same patient demonstrates intense enhancement of the mural nodule (arrow), with mild displacement of amygdala inferiorly.
FIG 11. Four-year-old boy with gelastic seizures. Axial FLAIR (A) and sagittal T1 (B) show a round, nonenhancing mass (arrow), contiguous with tuber cinereum within the hypothalamus. Mass is isointense on T1 and slightly hyperintense on T2. There was no enhancement after gadolinium administration. This patient’s gelastic seizures were refractory to medical therapy for 2 years. (B) Sagittal T1.
244
Curr Probl Diagn Radiol, November/December 2007
FIG 12. Seven-year-old girl patient with arteriovenous malformation (AVM). (A) Contrast-enhanced CT shows partially enhancing right frontoparietal mass that could represent a slow growing tumor or AVM. (B) Axial T2W MRI demonstrates hypointense signal intensity hemosiderin rim around the predominantly hyperintense mass, a vascular malformation. The mass contains signal voids which may represent vascular flow void or calcification. CT showed that they were not calcified. The presence of compact collections of vascular tangle connecting feeding arteries to prominent draining veins without an intervening capillary network helps establish a diagnosis of AVM.
FIG 13. Seventeen-year-old male with cavernous malformation. (A) Hallmark of cavernous malformation is the popcorn appearance on MR with a T2 dark rim, and a T2 bright center (arrow). (B) Coronal GRE sequence shows blooming (arrow). (C) Axial noncontrast CT demonstrates hyperdense heterogeneous lesion on the right frontal convexity, not as diagnostic as MRI.
Curr Probl Diagn Radiol, November/December 2007
245
REFERENCES 1. Ball WS. A clinical approach to imaging in childhood epilepsy. Pediatric Neuroradiology, Jr. New York: Lippincott-Raven, Chapter 12. p. 489-504. 2. Melhem ER, Hoon AH, Ferrucci JT, et al. Periventricular leukomalacia: Relationship between lateral ventricular volume on brain MRI and severity of cognitive and motor impairment. Radiology 2000;214:199-204. 3. Bronen RA, Fulbright RK, Kim JH, et al. A systematic approach for interpreting MR images of the seizure patient. AJR 1997;169:241-7.
246
4. Bradley WG, Shey R. How do I do it? MR imaging evaluation of seizures. Radiology 2000;214:651-6. 5. Wyllie E, Comair Y, Kotagal P, et al. Seizure outcome after epilepsy surgery in children and adolescents. Ann Neurol 1998;44:740-8. 6. Dobyns WB, Truwit CL. Lissencephaly and other malformations of cortical development. Neuropediatrics 1995;26:132-47. 7. Bien CG, Granata T, Antozzi C, et al. Pathogenesis, diagnosis and treatment of Rasmussssen encephalitis. A European consensus statement. Brain 2005;128:454-71. 8. Urbach H, Hattingen J, Von Oertzen J, et al. MRI in the presurgical work up of patients with drug resistant epilepsy. AJNR 2004;25:919-26.
Curr Probl Diagn Radiol, November/December 2007