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Hemimegalencephaly
Anne G. Osborn, MD, FACR; Blaise V. Jones, MD
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KEY FACTS

  • Terminology

    • Imaging

      • Pathology

        • Clinical Issues

          TERMINOLOGY

          • Abbreviations

            • Hemimegalencephaly (HMEG)
          • Synonyms

            • HMEG probably misnomer as < 1 whole hemisphere often involved (so-called hemi-hemimegalencephaly)
            • Dysplastic megalencephaly (generic for all forms of segmental brain overgrowth with cortical dysplasia)
          • Definitions

            • Hamartomatous overgrowth of part/all of hemisphere
            • Defect of cellular organization, neuronal migration

          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

                                            1. Re TJ et al: Magnetic Resonance Fiber Tracking in a Neonate with Hemimegalencephaly. J Neuroimaging. ePub, 2015
                                            2. Sarnat HB et al: Timing in Neural Maturation: Arrest, Delay, Precociousness, and Temporal Determination of Malformations. Pediatr Neurol. 52(5):473-486, 2015
                                            3. Santos AC et al: Hemispheric dysplasia and hemimegalencephaly: imaging definitions. Childs Nerv Syst. 30(11):1813-21, 2014
                                            4. Sarnat HB et al: Infantile tauopathies: Hemimegalencephaly; tuberous sclerosis complex; focal cortical dysplasia 2; ganglioglioma. Brain Dev. ePub, 2014
                                            5. 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
                                            6. Poduri A et al: Somatic mutation, genomic variation, and neurological disease. Science. 341(6141):1237758, 2013
                                            7. 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
                                            8. Poduri A et al: Somatic activation of AKT3 causes hemispheric developmental brain malformations. Neuron. 74(1):41-8, 2012
                                            9. 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
                                            10. Kwan SY et al: Corpus callosotomy in a patient of hemimegalencephaly and Lennox-Gastaut syndrome. Brain Dev. 30(10):643-6, 2008
                                            11. Guerra MP et al: Intractable epilepsy in hemimegalencephaly and tuberous sclerosis complex. J Child Neurol. 22(1):80-4, 2007
                                            12. Di Rocco C et al: Hemimegalencephaly: clinical implications and surgical treatment. Childs Nerv Syst. 22(8):852-66, 2006
                                            Related Anatomy
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                                            Related Differential Diagnoses
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                                            References
                                            Tables

                                            Tables

                                            KEY FACTS

                                            • Terminology

                                              • Imaging

                                                • Pathology

                                                  • Clinical Issues

                                                    TERMINOLOGY

                                                    • Abbreviations

                                                      • Hemimegalencephaly (HMEG)
                                                    • Synonyms

                                                      • HMEG probably misnomer as < 1 whole hemisphere often involved (so-called hemi-hemimegalencephaly)
                                                      • Dysplastic megalencephaly (generic for all forms of segmental brain overgrowth with cortical dysplasia)
                                                    • Definitions

                                                      • Hamartomatous overgrowth of part/all of hemisphere
                                                      • Defect of cellular organization, neuronal migration

                                                    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

                                                                                      1. Re TJ et al: Magnetic Resonance Fiber Tracking in a Neonate with Hemimegalencephaly. J Neuroimaging. ePub, 2015
                                                                                      2. Sarnat HB et al: Timing in Neural Maturation: Arrest, Delay, Precociousness, and Temporal Determination of Malformations. Pediatr Neurol. 52(5):473-486, 2015
                                                                                      3. Santos AC et al: Hemispheric dysplasia and hemimegalencephaly: imaging definitions. Childs Nerv Syst. 30(11):1813-21, 2014
                                                                                      4. Sarnat HB et al: Infantile tauopathies: Hemimegalencephaly; tuberous sclerosis complex; focal cortical dysplasia 2; ganglioglioma. Brain Dev. ePub, 2014
                                                                                      5. 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
                                                                                      6. Poduri A et al: Somatic mutation, genomic variation, and neurological disease. Science. 341(6141):1237758, 2013
                                                                                      7. 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
                                                                                      8. Poduri A et al: Somatic activation of AKT3 causes hemispheric developmental brain malformations. Neuron. 74(1):41-8, 2012
                                                                                      9. 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
                                                                                      10. Kwan SY et al: Corpus callosotomy in a patient of hemimegalencephaly and Lennox-Gastaut syndrome. Brain Dev. 30(10):643-6, 2008
                                                                                      11. Guerra MP et al: Intractable epilepsy in hemimegalencephaly and tuberous sclerosis complex. J Child Neurol. 22(1):80-4, 2007
                                                                                      12. Di Rocco C et al: Hemimegalencephaly: clinical implications and surgical treatment. Childs Nerv Syst. 22(8):852-66, 2006