Asymmetric Cerebral Hemispheres

Gregory L. Katzman, MD, MBA

DIFFERENTIAL DIAGNOSIS

Common

Normal Variant
Encephalomalacia, General
- Post-Ischemic Encephalomalacia
- Post-Traumatic Encephalomalacia
- Post-Inflammatory Encephalomalacia
Contusion/Traumatic Cerebral Edema
Cerebral Ischemia-Infarction, Acute
Cerebral Infarction, Chronic
Alzheimer Dementia
Multi-Infarct Dementia
CMV, Congenital
Frontotemporal Dementia
Dyke-Davidoff-Masson

Less Common

Hypoxic Ischemic Encephalopathy
Encephalitis
Sturge-Weber Syndrome
Plagiocephaly
MELAS
Hemimegalencephaly of Tuberous Sclerosis

Rare but Important

Hemimegalencephaly (Sporadic or Familial)
Pachygyria-Polymicrogyria
Gliomatosis Cerebri
Epidermal Nevus Syndrome
Schizencephaly
Encephalocraniocutaneous Lipomatosis
Proteus Syndrome

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Differential diagnosis list is vast and could logically be subdivided as follows
- One hemisphere larger than the other
- One hemisphere smaller than the other

Helpful Clues for Common Diagnoses

Normal Variant
- Minor asymmetry of otherwise normal appearing density/intensity parenchyma
- Substantial individual diversity of left-right gyral cerebral cortex asymmetries
- Cerebral asymmetry patterns are not universal & show variation based on origin
Encephalomalacia, General
- All etiologies appear as CSF replacing destroyed parenchyma due to
  - Post-ischemic loss of tissue following parenchymal hypoxic cell death
  - Post-traumatic loss from parenchymal irreversible traumatic insult
  - Post-inflammatory loss by irreversibly injured tissue
- Post-Traumatic Encephalomalacia
  - Parenchymal loss replaced by CSF
  - Occur in characteristic locations where brain is adjacent to bony protuberance or dural fold
Contusion/Traumatic Cerebral Edema
- Patchy superficial hemorrhages within edematous background, loss of gray-white distinction
- Swelling with loss of sulci, fissures, & cisterns
Cerebral Ischemia-Infarction, Acute
- Early cortical swelling in defined vascular distribution(s)
- DWI restriction with correlating ADC map
Cerebral Infarction, Chronic
- Volume loss with gliosis along margins
- Loss in a defined vascular distribution
Alzheimer Dementia
- Parietal & temporal cortical atrophy with disproportionate hippocampal volume loss
- Often affects brain asymmetrically
Multi-Infarct Dementia
- Multifocal infarcts of gray matter, white matter, basal ganglia, pons
- Usually bilateral, but may be unilateral
CMV, Congenital
- Microcephaly, cerebral calcification, cortical gyral abnormalities, cerebellar hypoplasia, & myelin delay or destruction
- Gestational age at time of infection determines pattern of CNS injury
Frontotemporal Dementia
- Caused by focal cortical atrophy involving frontal &/or temporal lobes
- Worse atrophy of dominant hemisphere
Dyke-Davidoff-Masson
- Cerebral hemiatrophy with ipsilateral hypertrophy of the skull and sinuses
- Caused by an intrauterine or perinatal carotid artery infarction

Helpful Clues for Less Common Diagnoses

Hypoxic Ischemic Encephalopathy
- Acquired neonatal condition generally attributed to cerebral hypoperfusion
- Several brain injury patterns attributed to differing clinical variables
Encephalitis
- Abnormal T2 hyperintensity of gray matter ± white matter, or deep gray nuclei
- Diffuse brain parenchymal inflammation caused by a variety of pathogens, most commonly viruses
Sturge-Weber Syndrome
- Cortical Ca++, atrophy, and enlarged ipsilateral choroid plexus
- Unilateral 80%, bilateral 20%; occipital > parietal > frontal/temporal lobes > diencephalon/midbrain > cerebellum
Plagiocephaly
- CT: Osseous asymmetry with thickened & sclerotic suture margins
- Premature unilateral closure of coronal &/or lambdoidal sutures
MELAS
- Stroke-like cortical lesions crossing typical vascular territories
- Acute → gyriform swelling; chronic → atrophy
Hemimegalencephaly of Tuberous Sclerosis
- Unilateral lobar/hemispheric overgrowth
- Look for other markers of TSC (e.g., subependymal nodules)

Helpful Clues for Rare Diagnoses

Hemimegalencephaly (Sporadic or Familial)
- Hamartomatous overgrowth of hemisphere
- Defect of cellular organization, neuronal migration
Pachygyria-Polymicrogyria
- Findings range from incomplete lissencephaly to excessively small & prominent gyral convolutions
- Disorder of neuronal migration
Gliomatosis Cerebri
- T2 hyperintense infiltrating mass with enlargement of involved hemisphere
- Typically hemispheric white matter involvement, involves cortex in 19%
Epidermal Nevus Syndrome
- Hemimegalencephaly is most common CNS abnormality
- Also migration abnormalities, vascular malformations, corpus callosal agenesis, Dandy-Walker, myelomeningocele, Chiari malformations, & tumors
Schizencephaly
- Transmantle gray matter lined clefts
- “Closed-lip” (small) or “open-lip” (large)
Encephalocraniocutaneous Lipomatosis
- Hemispheric atrophy, ventriculomegaly with ipsilateral alopecia overlying a scalp lipoma
- Hydrocephalus is frequently present
Proteus Syndrome
- Complex hamartomatous disorder involving half the body
- CNS: Hemimegalencephaly, subependymal calcified nodules, & periventricular cysts