Hydranencephaly and porencephaly are rare, related malformations associated with failure of development (hypoplasia) and destruction (secondary atrophy) of primarily the neopallial part of the telencephalon (the neocortex and the ventricular zone). The pathogenesis of this anomaly is not always certain.
With porencephaly, these cavities are usually filled with cerebrospinal fluid in the brain's parenchyma, usually connecting the ventricles to the brain surface. The lesion are associated with ischemic or hemorrhagic episodes and is characterized by a cavity, or cavitations in brain tissue, of variable size and location, given different names according to presumed mechanism and morphology.
Unlike hydrocephalus, which is characterized by an expansive fluid-filled cavity which continues to worsen both physiologically and clinically, porencephaly is usually a stable, degenerative pathology.
These conditions may also be caused by prenatal forebrain infarcts.
Clinical symptoms included a history of generalized weakness, muscle atrophy, reluctance to move, ataxia, hypermetria, episodes of generalized tonic-clonic seizures, abnormal nystagmus, ataxia and increased myotatic reflexes. Dogs from 12 weeks of age to 7 years may be affected and although the defects develop intrauterine or postnatal, the clinical symptoms can occur later in life.
Radiographic imaging and CSF analysis are usually normal. MRI imaging may reveal extensive cystic changes of the cerebral hemispheres.
Diagnosis, unfortunately, is often achieved on postmortem, with porencephalic lesions appearing as wedge-shaped parenchymal defects connecting the ventricular system and the subarachnoid space or as large cystic defects in the cerebral hemispheres. Porencephaly is often accompanied by amygdalar-hippocampal atrophy, which is usually related to the occurrence of seizures.
A differential diagnosis would include vestibular disease, cerebellar abiotrophy, myelodysraphism, idiopathic epilepsy, encephalitis, hydrocephalus, holoprosencephaly, corpus callosum agenesis/dysgenesis, lissencephaly, polymicrogyria, meningoencephalocele, intracranial cysts, cerebellar malformations, and hamartomas.
There is no specific treatment for this condition.
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