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Porencephalic Cyst


KEY FACTS

Terminology

  • Cerebrospinal fluid (CSF)-filled parenchymal cavity

    • Deep, unilateral/bilateral cavity/excavation

    • Usually communicates with ventricle &/or subarachnoid space

    • Lined by reactive gliosis/astrocytic proliferation

  • Congenital (perinatal brain destruction) or acquired (trauma, infection, etc)

Imaging

  • Best diagnostic clue: CSF-filled cavities with enlarged adjacent ventricle

  • MR: Smooth-walled cavity; CSF isointense; lined by gliotic white matter

Top Differential Diagnoses

  • Consider arachnoid, ependymal, neoplastic, or inflammatory cyst

  • Encephalomalacia

  • Schizencephaly

  • Dandy-Walker malformation

  • Agenesis of corpus callosum with doral interhemispheric cyst

  • Hydranencephaly

Pathology

  • Congenital: In utero destructive process caused by cerebral vascular events or infectious injury

  • Acquired: Injury later in life, following head trauma, surgery, vascular occlusion, or infection

  • Genetics: Rare, autosomal dominant familial porencephaly → procollagen defect

Clinical Issues

  • Spastic hemiplegia most common symptom

  • Indications for therapy: Mass effect, localized/generalized refractory symptoms

Coronal graphic illustrates an intraparenchymal CSF-filled cavity that communicates with the left lateral ventricle and subarachnoid space. Note the classic porencephalic cyst is lined with gliotic white matter
.

Lateral view of autopsied brain with a porencephalic cyst in the temporal lobe shows a CSF-filled cavity that extends from the brain surface
to the ventricular ependyma of the temporal horn
. The cyst is lined with gliotic white matter.

(Courtesy J. Townsend, MD.)

Axial FLAIR of a porencephalic cyst shows a CSF intensity parenchymal defect, which was isointense to CSF on all sequences, including suppression on FLAIR
. Note the small amount of associated white matter gliosis
. Susceptibility artifact is secondary to a ventriculostomy shunt
.

Coronal T1 C+ MR in the same patient shows a CSF-density parenchymal defect
, which communicates with the atrium of the left lateral ventricle with dilatation of the occipital horn
. Classic porencephalic cyst is also seen.

TERMINOLOGY

Synonyms

  • Porencephaly

Definitions

  • Various definitions of porencephaly

    • Congenital/acquired CSF-filled cavity that usually communicates with ventricular system

      • –

        Deep, unilateral/bilateral cavities or excavations

      • –

        Lined by reactive gliosis/astrocytic proliferation

    • Presence of cysts/cavities in brain parenchyma

      • –

        Communicating by “pore” with arachnoid space

    • Cavities arising in fetal life or early infancy

      • –

        Brain destruction during perinatal period

      • –

        Frequently communicate with subarachnoid space &/or lateral ventricles

IMAGING

General Features

  • Best diagnostic clue

    • CSF-filled cavities; enlarged adjacent ventricle

  • Location

    • Often corresponds to territories supplied by cerebral arteries (ischemic injury in midgestation)

    • Cortical/subcortical cavity, unilateral/bilateral

    • Usually connected with a lateral ventricle

  • Size

    • Varies from small to enormous

CT Findings

  • NECT

    • Intraparenchymal smooth-walled cavity

      • –

        Isodense with CSF

    • Directly communicates with ventricle

    • May see thin membrane separating cavity from ventricle

  • CECT

    • No contrast enhancement of fluid-filled cavity

  • Bone CT

    • Skull remodeling from chronic CSF pulsation

  • CTA

    • Absence of vessels at site of porencephaly

MR Findings

  • T1WI

    • Smooth-walled cavity; CSF isointense; lined by WM

  • T2WI

    • Brain atrophy, gliosis common; CSF isointense; lined by white matter

  • FLAIR

    • Accurately depicts CSF content of cyst and gliosis

  • T1WI C+

    • Nonenhancing cyst

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