Intraoperative ultrasonography as a guide to patient selection for duraplasty after suboccipital decompression in children with Chiari malformation Type I

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Object

Indications for duraplasty in treatment of Chiari malformation Type I (CM-I) remain unclear. In the present study, the authors evaluate their surgical experience to determine whether intraoperative ultrasonography is effective in the selection of patients with CM-I who can be adequately treated with craniectomy alone without duraplasty.

Methods

The authors reviewed the records of 256 children who underwent first-time hindbrain decompression for CM-I. Craniectomy alone (without duraplasty) was performed when intraoperative ultrasonography suggested adequate decompression of the subarachnoid spaces ventral and dorsal to the tonsils after suboccipital craniectomy alone. Duraplasty was performed if intraoperative ultrasonography demonstrated persistent dural compression of the tonsils following craniectomy. Symptom recurrence as a function of time was compared between cases of duraplasty versus suboccipital decompression alone stratified by extent of tonsillar herniation.

Results

Duraplasty was performed in 140 patients (55%), and suboccipital decompression alone was performed in 116 patients (45%). Patients underwent follow-up for 29 ± 15 months. Symptoms included headache in 192 patients (75%) and lower cranial nerve and brainstem dysfunction in 68 (27%). In 38 patients (15%) there was tonsillar herniation rostral to the C-1 lamina, in 195 (76%) it extended between the C-1 and C-2 lamina, and in 23 patients (9%) there was herniation caudal to the lower border of the C-2 lamina. In children with tonsillar herniation caudal to C-1, ultrasonography-guided suboccipital decompression alone was associated with a 2-fold increase in the risk of symptom recurrence compared with those who also underwent duraplasty (p = 0.01). In children with tonsillar herniation rostral to C-1, outcome was equivalent between suboccipital decompression alone and duraplasty (p = 0.41).

Conclusions

In the setting of moderate-to-severe tonsillar CM-I, intraoperative ultrasonography demonstrating decompression of the subarachnoid spaces ventral and dorsal to the tonsils may not effectively select patients in whom bone decompression alone is sufficient. Duraplasty may be warranted in cases of tonsillar herniation that extends below the C-1 lamina regardless of intraoperative ultrasonography findings. More objective cerebrospinal fluid flow or volumetric measures may be needed intraoperatively to guide duraplasty in patients with more pronounced tonsillar herniation.

Abbreviations used in this paper: CI = confidence interval; CM-I = Chiari malformation Type I; CSF = cerebrospinal fluid; OR = odds ratio.

Article Information

Address correspondence to: Matthew J. McGirt, M.D., 3553 Newland Road, Baltimore, Maryland 21218. email: mmcgirt1@jhmi.edu.

© AANS, except where prohibited by US copyright law.

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Figures

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    Kaplan–Meier plots of treatment failure (defined as recurrence of symptoms) as a function of time after first surgery in children with CM-I. A: Symptom recurrence did not differ as a function of duraplasty versus suboccipital decompression alone in patients with tonsillar herniation > 5 mm below the foramen magnum but rostral to the C-1 lamina (p = 0.41). B: Despite intraoperative ultrasonographic evidence of adequate hindbrain decompression, suboccipital decompression alone was associated with a 2-fold increase (p < 0.05) in risk of treatment failure in patients with tonsillar herniation between C-1 and C-2. C: A 1.5-fold increase (p < 0.05) in risk of treatment failure is demonstrated in patients with tonsillar herniation caudal to the lower border of the C-2 lamina.

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