There are few published data on the natural history of “benign” Chiari I malformation; i.e., Chiari with minimal or no symptoms at presentation and no imaging evidence of syrinx, hydrocephalus or spinal cord signal abnormality. The purpose of this study is to review a large cohort of children with benign Chiari I malformation and to determine whether these children become symptomatic and require surgical treatment.
Patients were identified from institutional outpatient records using ICD-9 diagnosis codes for Chiari I malformation from 1998 to 2016. After review of the medical records, patients were excluded if they: 1. did not have a diagnosis of Chiari I malformation, 2. were not evaluated by a neurosurgeon, 3. had previously undergone posterior fossa decompression, or 4. had imaging evidence of syringomyelia at their first appointment. To include only “benign” Chiari (without syrinx or classic Chiari symptoms that could prompt immediate intervention), any patient who underwent decompression within nine months of initial evaluation was excluded. After a detailed chart review, patients were excluded if they had classical Chiari malformation symptoms at presentation. We then determined what changes in the clinical picture prompted surgical treatment. Patients were excluded listwise from the multivariate logistic regression analysis if they had missing data such as “race” and “insurance”; however, these patients were included in the overall survival analysis
A total of 427 patients were included for analysis with a median follow-up duration of 25.5 months (range: 0.17-179.1 months). Fifteen patients had surgery at a median time of 21.0 months (range: 11.3-139.3 months). The most common indications for surgery were tussive headache in five (33.3%), syringomyelia in five (33.3%), and non-Chiari headache in five (33.3%). Using the Kaplan-Meier method, freedom from posterior fossa decompression was 95.8%, 94.1%, and 93.1% at three, five, and 10 years respectively.
Among a large cohort of patients with “benign” Chiari I malformation, progression of imaging abnormalities or symptoms that warrant surgical treatment is infrequent. Therefore, these patients should be managed conservatively. However, clinical follow-up of such individuals is justified as there is a low, but non-zero, rate of development of new symptoms or syringomyelia. Future analyses will determine whether imaging or clinical features present at initial evaluation are associated with progression and future need for treatment.