Purpose or Case Report: The optic nerve sheath diameter (ONSD) has been noted to distend in patients with increased intracranial pressure. There is relatively little data on the sensitivity of dilated optic nerve sheath on initial CT or MRI as a sign of raised Intracranial pressure (ICP) in children with ventriculoperitoneal (VP) shunt malfunction. This pilot study aims to establish if there is a significant difference in ONSD pre- and postshunt revision surgery.
Methods & Materials: A retrospective review of pre and post surgical head CT and MRI images from 34 patients who underwent VP shunt revision from Jan2013 to Sept 2016 at a tertiary care pediatric hospital. Two patients were excluded due to nonavailability of imaging as were 7 patients with pre and post-surgical imaging on different modalities. The optic nerve was unevaluable on CT in one patient. A total of 24 optic nerves, right or left side, were measured pre and post surgery. 11 optic nerves were evaluated on CT (pre and post), 13 on MRI (pre and post). The ONSD measure was done at 3 mm depth behind the globe in axial images (CT or T2 W MRI) by a pediatric radiologist in blinded fashion. The data were analysed in 3 groups: CT, MR and both combined. Pre and post ONSD data were compared using a non-parametric t paired t-test (Wilcoxon signed rank test). Two-tailed p-values with statistical significance set at p=0.05.
Results: A total of 24 patients (9 girls and 11 boys) with pre and post CT or MRI scan of the head were selected with mean age of 7 years. There were significant differences in the diameter of the optic nerve between the pre and post surgical images in all three groups( p < 0.05). Diameter of the optic nerve sheath was significantly higher in pre surgical images compared to post surgical images (Table 1).
Conclusions: In children undergoing VP shunt revision for shunt dysfunction, the optic nerve sheath diameter is significantly larger in presurgical images than in post surgery control images. Changes in ONSD could potentially help diagnose shunt dysfunction.