A late complication of CSF shunting: acquired Chiari I malformation.

PURPOSE: Acquired Chiari I malformation developing after cerebrospinal fluid (CSF) shunting is an intriguing late complication of CSF shunt surgery and not only raises questions as to its pathogenesis but also poses many queries about the possible adverse effects on the subsequent child development as well as on the indications and possibilities of surgical correction.

MATERIALS AND METHODS: We report a series of 17 patients with the neuroradiological evidence of an "acquired" Chiari type I malformation. These patients, 3 to 24 years (mean 11.3 years), had been treated previously with an extrathecal CSF shunt. The follow-up varied from 2 to 12 years (mean, 6).

RESULTS: Neuroradiological investigation demonstrated a small posterior cranial fossa, small ventricles, markedly reduced periencephalic subarachnoid spaces, and thickening of the skull vault and base. The degree of tonsillar herniation did not correlate with clinical manifestations. All patients with severe clinical manifestations or with progressive worsening of neuroradiological findings were considered for surgical treatment. Decompressive supratentorial craniotomy seemed to fit with the purpose of enlarging the intracranial volume without the risk of aggravating the hindbrain herniation. An immediate relief of clinical manifestations was observed in all patients. Not surgically treated patients did not show any clinical or radiological modification during all the follow-up.

CONCLUSIONS: This study contributes to the understanding of the underlying pathogenetic mechanisms of acquired Chiari type 1 malformation in cases of long-lasting supratentorial CSF shunting and provides a base for planning the best management, whether conservative or surgical.