Multicystic encephalomalacia

This is part 4 of our Neonatal Brain Ultrasound Series!

Case:

A 1-month-old, born full-term, now admitted for poor feeding, seizures, and profound developmental delay. At birth, the infant suffered severe hypoxic-ischemic encephalopathy following placental abruption and was treated with therapeutic hypothermia. 

Here are the sweeps from the brain ultrasound exam:

Coronal Sweep:

Coronal zoomed:

Sagittal swipe:

The brain US study reveals severe, bilateral multicystic encephalomalacia.

What are the sonographic features of this disease entity?

A) Several big cysts with regular margins

B) multiple irregular, fluid-filled cysts and septations (honeycomb appearance)

C) increased periventricular echogenicity

Explanation:

The study reveals severe, bilateral multicystic encephalomalacia. The normal brain architecture of the cerebral hemispheres has been replaced by multiple, irregular anechoic (fluid-filled) cysts separated by echogenic septae, creating a "honeycomb" or "swiss cheese" appearance.

Prevalence and Etiology:

Multicystic encephalomalacia is a very rare but devastating end-stage manifestation of massive brain insult. The location of the lesions varies with the nature of the insult. While leukomalacia typically targets specific white matter zones, MCE reflects a global "liquefactive necrosis" that consumes both the white matter and the overlying cortex. It is most commonly the result of profound Hypoxic-Ischemic Encephalopathy (HIE) in term infants, often triggered by events like the placental abruption seen in this case. Other rare causes include severe neonatal infections or head trauma. 

Prognosis:

Due to the selective vulnerability of brain tissue, the basal ganglia, thalami, and brainstem are occasionally spared from the initial hypoxic-ischemic insult; this allows for the preservation of basic vegetative functions (such as breathing and heart rate), meaning these infants may survive for years while remaining at a neonatal developmental level. Palliative care is the standard of practice for MCE, as there is currently no neuroregenerative therapy capable of restoring the destroyed parenchymal architecture.

Imaging:

Ultrasonography is the most sensitive modality for detecting glial septa, but it is less useful for comprehensive assessment of the brain; therefore, MRI is required to evaluate the extent of parenchymal destruction. An important differential diagnosis of multicystic encephalomalacia (MCE) is subcortical and/or periventricular leukomalacia, which can appear similar. However, ultrasound and MRI help distinguish these entities. Multicystic encephalomalacia demonstrates diffuse replacement of brain tissue by multiple large, irregular cysts, with severe loss of normal architecture and passive ventricular enlargement, involving both gray and white matter. In contrast, periventricular leukomalacia is confined to the periventricular white matter, initially appearing as persistent increased echogenicity and later evolving into small cysts adjacent to the lateral ventricles, while overall brain structure remains relatively preserved.

Don't forget to read our previous blog posts on sonoanatomy with a focus on midline structures, subependymal pseudocysts and subcortical leukomalacia.