Multiple Hypodense Parenchymal Lesions

Karen L. Salzman, MD

DIFFERENTIAL DIAGNOSIS

Common

Cerebral Infarction
Trauma
- Cerebral Contusion
- Diffuse Axonal Injury (DAI)
Metastases, Parenchymal

Less Common

Multiple Sclerosis
Infection
- Encephalitis (Miscellaneous)
- Abscesses
- Opportunistic Infection, AIDS
- Tuberculosis
ADEM
Acute Hypertensive Encephalopathy, PRES
Vasculitis

Rare but Important

Glioblastoma Multiforme
Osmotic Demyelination Syndrome
Tuberous Sclerosis Complex
Lyme Disease
Systemic Lupus Erythematosus
CADASIL
Rickettsial Diseases
Lymphoma, Intravascular (Angiocentric)

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Includes multiple parenchymal lesions hypodense to brain but hyperdense compared to CSF
Cysts & cyst-like lesions are excluded

Helpful Clues for Common Diagnoses

Cerebral Infarction
- Wedge-shaped area of hypodensity in a vascular distribution classic
- Hypodensity increases with age of infarct
  - Acute: Subtle hypodensity
  - Subacute: ↑ Hypodensity & edema
  - Chronic: Gliosis/encephalomalacia with volume loss typical
- Cerebral hemispheres > posterior fossa
- Often in a single vascular distribution
- May appear as multiple lesions if embolic
Trauma
- DAI & cerebral contusions typically hemorrhagic (hyperdense)
- Trauma history is usually known
Cerebral Contusion
- Brain surface injuries involving superficial gray matter (GM) & contiguous subcortical white matter (WM)
- Classic location: Anterior inferior frontal lobes & inferior temporal lobes
- Hemorrhagic > nonhemorrhagic
- Soft tissue injury in 70% of patients
Diffuse Axonal Injury (DAI)
- Punctate hemorrhages at corticomedullary junction, corpus callosum, deep GM, & upper brainstem classic
- CT often normal acutely (50-80%)
- May see small hypodense edematous foci
- Petechial hemorrhage in up to 50%
Metastases, Parenchymal
- Multifocal enhancing lesions with edema at corticomedullary junctions

Helpful Clues for Less Common Diagnoses

Multiple Sclerosis
- Multiple hypodense periventricular lesions
- Variable enhancement
- Young adult presentation common
Infection
- Pattern of brain involvement may help differentiate various etiologies
- Fungal & parasitic infections less common
Encephalitis (Miscellaneous)
- Viral agents most common
- Many involve deep gray nuclei
- Hypodense lesions with patchy enhancement common
- Herpes encephalitis most common agent
  - Predilection for limbic system
  - Involves cortex and subcortical WM
  - Bilateral, asymmetric involvement
Abscesses
- Four pathologic stages: Early cerebritis, late cerebritis, early capsule, late capsule
- Imaging varies with abscess stage
- Bacterial > > fungal/parasitic
- Multiple often related to septic emboli
- Frontal, parietal lobes commonly involved
Opportunistic Infection, AIDS
- Toxoplasmosis: Multiple ring-enhancing lesions of varying size with surrounding edema in deep & superficial brain
- PML: Large multifocal subcortical WM lesions without mass effect, enhancement
- TB & fungal: Solid, mildly hyperdense or hypodense masses
Tuberculosis
- Basilar meningitis + parenchymal lesions highly suggestive
- Tuberculomas: Hypodense parenchymal masses with solid or ring enhancement
- Meningitis is most frequent manifestation of CNS TB & is more common in children
ADEM
- Multifocal WM &/or basal ganglia (BG) lesions after infection or vaccination
- Hypodense flocculent, asymmetric lesions
- Initial CT normal in 40%
Acute Hypertensive Encephalopathy, PRES
- Patchy cortical/subcortical PCA territory lesions in a hypertensive patient
- Posterior parietal, occipital lobes > BG, posterior fossa
- Usually bilateral, often asymmetric
Vasculitis
- Characterized by non-atheromatous inflammation & blood vessel wall necrosis
- May see multifocal low density areas in subcortical WM, BG
- Initial CT often normal; angiography remains gold standard