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KEY FACTS
Terminology
Imaging
Pathology
Clinical Issues
Diagnostic Checklist
TERMINOLOGY
Definitions
- Megalencephaly: Brain size & weight > 2 standard deviations above age-related normals
- Hemimegalencephaly (HME): Hamartomatous overgrowth of part vs. entire hemisphere
- Classic HME (or unilateral megalencephaly): Holohemispheric involvement
- Partial HME (or focal megalencephaly): Portion of hemisphere involved
- Difficult to distinguish from focal cortical dysplasia
- Total HME: Involvement of unilateral cerebral hemisphere, cerebellum, & brainstem (rare)
IMAGING
General Features
CT Findings
MR Findings
Ultrasonographic Findings
Nuclear Medicine Findings
Imaging Recommendations
DIFFERENTIAL DIAGNOSIS
PATHOLOGY
General Features
Gross Pathologic & Surgical Features
Microscopic Features
CLINICAL ISSUES
Presentation
Demographics
Natural History & Prognosis
Treatment
DIAGNOSTIC CHECKLIST
Consider
Image Interpretation Pearls
Reporting Tips
Selected References
- Crino PB: Focal Cortical Dysplasia. Semin Neurol. 35(3):201-8, 2015
- Re TJ et al: Magnetic resonance fiber tracking in a neonate with hemimegalencephaly. J Neuroimaging. 25(5): 844-7, 2015
- Kamiya K et al: Accelerated myelination along fiber tracts in patients with hemimegalencephaly. J Neuroradiol. 41(3):202-10, 2014
- Mirzaa GM et al: Megalencephaly and hemimegalencephaly: breakthroughs in molecular etiology. Am J Med Genet C Semin Med Genet. 166C(2):156-72, 2014
- Wang DD et al: Unilateral holohemispheric central nervous system lesions associated with medically refractory epilepsy in the pediatric population: a retrospective series of hemimegalencephaly and Rasmussen's encephalitis. J Neurosurg Pediatr. 1-12, 2014
- Williams F et al: The diagnosis of hemimegalencephaly using in utero MRI. Clin Radiol. 69(6):e291-7, 2014
- Honda R et al: Long-term developmental outcome after early hemispherotomy for hemimegalencephaly in infants with epileptic encephalopathy. Epilepsy Behav. 29(1):30-5, 2013
- Poduri A et al: Somatic mutation, genomic variation, and neurological disease. Science. 341(6141):1237758, 2013
- Barkovich A et al: Pediatric Neuroimaging. 5th ed. Philadelphia: Lippincott Williams & Wilkins. p. 407-409, 2012
- Lee JH et al: De novo somatic mutations in components of the PI3K-AKT3-mTOR pathway cause hemimegalencephaly. Nat Genet. 44(8):941-5, 2012
- Rivière JB et al: De novo germline and postzygotic mutations in AKT3, PIK3R2 and PIK3CA cause a spectrum of related megalencephaly syndromes. Nat Genet. 44(8):934-40, 2012
- Soufflet C et al: The nonmalformed hemisphere is secondarily impaired in young children with hemimegalencephaly: a pre- and postsurgery study with SPECT and EEG. Epilepsia. 45(11):1375-82, 2004
- Flores-Sarnat L et al: Hemimegalencephaly: part 2. Neuropathology suggests a disorder of cellular lineage. J Child Neurol. 18(11):776-85, 2003
- Flores-Sarnat L: Hemimegalencephaly: part 1. Genetic, clinical, and imaging aspects. J Child Neurol. 17(5):373-84; discussion 384, 2002
- Ishibashi H et al: Somatosensory evoked magnetic fields in hemimegalencephaly. Neurol Res. 24(5):459-62, 2002
- Di Rocco F et al: Hemimegalencephaly involving the cerebellum. Pediatr Neurosurg. 35(5):274-6, 2001
- Arai Y et al: A comparison of cell phenotypes in hemimegalencephaly and tuberous sclerosis. Acta Neuropathol. 98(4):407-13, 1999
- Hanefeld F et al: Hemimegalencephaly: localized proton magnetic resonance spectroscopy in vivo. Epilepsia. 36(12):1215-24, 1995
Related Anatomy
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References
Tables
Tables
KEY FACTS
Terminology
Imaging
Pathology
Clinical Issues
Diagnostic Checklist
TERMINOLOGY
Definitions
- Megalencephaly: Brain size & weight > 2 standard deviations above age-related normals
- Hemimegalencephaly (HME): Hamartomatous overgrowth of part vs. entire hemisphere
- Classic HME (or unilateral megalencephaly): Holohemispheric involvement
- Partial HME (or focal megalencephaly): Portion of hemisphere involved
- Difficult to distinguish from focal cortical dysplasia
- Total HME: Involvement of unilateral cerebral hemisphere, cerebellum, & brainstem (rare)
IMAGING
General Features
CT Findings
MR Findings
Ultrasonographic Findings
Nuclear Medicine Findings
Imaging Recommendations
DIFFERENTIAL DIAGNOSIS
PATHOLOGY
General Features
Gross Pathologic & Surgical Features
Microscopic Features
CLINICAL ISSUES
Presentation
Demographics
Natural History & Prognosis
Treatment
DIAGNOSTIC CHECKLIST
Consider
Image Interpretation Pearls
Reporting Tips
Selected References
- Crino PB: Focal Cortical Dysplasia. Semin Neurol. 35(3):201-8, 2015
- Re TJ et al: Magnetic resonance fiber tracking in a neonate with hemimegalencephaly. J Neuroimaging. 25(5): 844-7, 2015
- Kamiya K et al: Accelerated myelination along fiber tracts in patients with hemimegalencephaly. J Neuroradiol. 41(3):202-10, 2014
- Mirzaa GM et al: Megalencephaly and hemimegalencephaly: breakthroughs in molecular etiology. Am J Med Genet C Semin Med Genet. 166C(2):156-72, 2014
- Wang DD et al: Unilateral holohemispheric central nervous system lesions associated with medically refractory epilepsy in the pediatric population: a retrospective series of hemimegalencephaly and Rasmussen's encephalitis. J Neurosurg Pediatr. 1-12, 2014
- Williams F et al: The diagnosis of hemimegalencephaly using in utero MRI. Clin Radiol. 69(6):e291-7, 2014
- Honda R et al: Long-term developmental outcome after early hemispherotomy for hemimegalencephaly in infants with epileptic encephalopathy. Epilepsy Behav. 29(1):30-5, 2013
- Poduri A et al: Somatic mutation, genomic variation, and neurological disease. Science. 341(6141):1237758, 2013
- Barkovich A et al: Pediatric Neuroimaging. 5th ed. Philadelphia: Lippincott Williams & Wilkins. p. 407-409, 2012
- Lee JH et al: De novo somatic mutations in components of the PI3K-AKT3-mTOR pathway cause hemimegalencephaly. Nat Genet. 44(8):941-5, 2012
- Rivière JB et al: De novo germline and postzygotic mutations in AKT3, PIK3R2 and PIK3CA cause a spectrum of related megalencephaly syndromes. Nat Genet. 44(8):934-40, 2012
- Soufflet C et al: The nonmalformed hemisphere is secondarily impaired in young children with hemimegalencephaly: a pre- and postsurgery study with SPECT and EEG. Epilepsia. 45(11):1375-82, 2004
- Flores-Sarnat L et al: Hemimegalencephaly: part 2. Neuropathology suggests a disorder of cellular lineage. J Child Neurol. 18(11):776-85, 2003
- Flores-Sarnat L: Hemimegalencephaly: part 1. Genetic, clinical, and imaging aspects. J Child Neurol. 17(5):373-84; discussion 384, 2002
- Ishibashi H et al: Somatosensory evoked magnetic fields in hemimegalencephaly. Neurol Res. 24(5):459-62, 2002
- Di Rocco F et al: Hemimegalencephaly involving the cerebellum. Pediatr Neurosurg. 35(5):274-6, 2001
- Arai Y et al: A comparison of cell phenotypes in hemimegalencephaly and tuberous sclerosis. Acta Neuropathol. 98(4):407-13, 1999
- Hanefeld F et al: Hemimegalencephaly: localized proton magnetic resonance spectroscopy in vivo. Epilepsia. 36(12):1215-24, 1995
