Abrupt foramen magnum syndrome due to shunt malfunction in a previously asymptomatic chiari I malformation: the hidden predictable risk in long-lasting shunted patients.

Cerebrospinal fluid overdrainage in long-lasting shunted hydrocephalus is a well recognized complication. It may lead to different clinical syndromes which may occur over time, namely cranioencephalic disproportion and hindbrain herniation. Among the latter, Chiari malformation type 1 classically refers to one of the mildest form. When symptomatic, the patients generally exhibit a chronic, slowly progressive disease course. Although well documented in Chiari type II malformation and hydrocephalus, ventriculo-peritoneal shunt malfunction causing acute neurological deterioration in acquired Chiari malformation type 1 has been described only in three cases. All these patients underwent urgent shunt revision and suboccipital decompression in two of them, achieving good clinical improvement. We report on a 20-year-old woman harboring a previously asymptomatic Chiari malformation type 1, who experienced an acute foramen magnum syndrome with ventriculo-peritoneal shunt malfunction. We performed an endoscopic third-ventriculo-cisternostomy and definite removal of the shunt, obtaining the complete resolution of symptoms and shunt independence at 2 years follow-up. The phisiopathogenetic mechanisms and surgical management are discussed.