Pitfalls in Chiari Malformation Type 1 Treatment: Possible Causes of Surgical Failures and Indications for Reoperation


There are still many discussions about surgical indications and techniques for Chiari I Malformation (CM), but there are few doubts that when there is an associated symptomatic or evolving Syringomyelia Craniovertebral Decompression with Durplasty is the first treatment. Failures of this first choice surgery are often complicated by progressive symptoms and slowly progressive neurological deterioration.


The present study concerns 42 cases of re-doing Chiari Surgery performed at the National Neurological Institute of Milan between 1986 and 2019; they represent less than 10% of cases (389) firstly operated at Besta in the same period. Mainly the patients came from other institutions: 17 redos had been operated in our institution at first and the remaining 25 had been operated elsewhere. We classified the cases by the possible cause of surgical failure: A: 9 uncomplete/wrong bone decompression B: 12 unperformed duroplasty C: 4 CSF leak with “compressive” collection D: 1 excessive bone opening with “CBL sinking” E: 1 syrynx fenestration and intracranial hypotension F: 3 arachnoiditis spontaneous or after untreated CSF collection G. 2 CranioVertebral Joint (CVJ) instability (due to an associated CVJ Malformation (CVJM) or secondary to excessive cervical bone demolition) H: 4 lack of tonsillar resection (in very low lying tonsils) I: 4 inadequate first surgery (as sectioning the filum) L: 3 unrecognized associated malformation (hydrocephalus and/or craniostenosis)

Treatment and Results

The surgical treatment was chosen on the basis of the “failure pathogenesis” subgroup. One common data and it will be discussed in detail; one common data of this re-do group is the high percentage (>50%) of patients deserving shunting/endoscopy for treatment of an associated Hydrocephalus, if compared with our firstsurgery series. Compared with the same series, there were some cases of surgical morbidity and one case of postoperative mortality, due to abdominal complications in an already highly compromised patient; despite a good response of the syringomielia to surgery, the neurological recovery was slow and uncomplete in the great majority of cases.


The follow-up of patients operated for CM1 with Syringomyelia should be performed carefully and extended at long-term, to avoid missing late failures, complicated by slowly progressive deterioration that uncomplete recovery also after successful second surgery. The results of these “second look” operations could be good if aimed to treat a recognized cause of failure. Often a CSF circulation permanent disturbance occurs, related to foramen magnum arachnoiditis, often needing a treatment by itself, as endoscopy or shunting.