Living with One Hemisphere — A Large Porencephalic Cyst

A 2-year-old girl presented with gait disturbance and difficulty using her right hand. She had been born by normal spontaneous delivery at 38 weeks of gestation after an uncomplicated pregnancy. On admission, she was found to have a normal head circumference and mild spastic right hemiparesis. Neuropsychological testing showed normal comprehension and social skills. She had mild bimanual dyspraxia and mild dysarthria. An electroencephalogram revealed reduced background activity in the left hemisphere. Magnetic resonance imaging of the brain revealed a large, left hemispheric, porencephalic cyst, with extension into the frontal, temporal, and occipital lobes (Panel A). Only residual rims of tissue were present in the frontal and temporal cortexes, the left thalamus, and the basal ganglia. The cerebellum was spared (Panel B). Magnetic resonance angiography (Panel C) revealed occlusive disease involving the left middle cerebral artery (arrowhead) and the posterior cerebral artery (asterisk), as well as hypoplasia of the A1 segment of the right anterior cerebral artery (arrow). There was no evidence of in utero infection; no other affected family members were identified. Despite severe hypoplasia and hypoperfusion of the left side of the brain, neurodevelopment was relatively preserved — the patient had only mild spasticity and a mild disorder of the fine motor sequences that govern speech, and her speech comprehension was affected very little.