Midline Brain Shift After Hemispheric Surgery: Natural History, Clinical Significance, and Association With Cerebrospinal Fluid Diversion

Abstract

Background: Hemispherectomy and its modern variants are effective surgical treatments for medically intractable unihemispheric epilepsy. Although some complications such as posthemispherectomy hydrocephalus are well documented, midline brain shift (MLBS) after hemispheric surgery has only been described anecdotally and never formally studied.

Objective: To assess the natural history and clinical relevance of MLBS and determine whether cerebrospinal fluid (CSF) shunting of the ipsilateral surgical cavity exacerbates MLBS posthemispheric surgery.

Methods: A retrospective review of consecutive pediatric patients who underwent hemispheric surgery for intractable epilepsy and at least 6 months of follow-up at UCLA between 1994 and 2018 was performed. Patients were grouped by MLBS severity, shunt placement, valve type, and valve opening pressure (VOP). MLBS was evaluated using the paired samples t-test and analysis of covariance adjusting for follow-up time and baseline postoperative MLBS.

Results: Seventy patients were analyzed, of which 23 (33%) required CSF shunt placement in the ipsilateral surgical cavity for posthemispherectomy hydrocephalus. MLBS increased between first and last follow-up for nonshunted (5.3 ± 4.9-9.7 ± 6.6 mm, P < .001) and shunted (6.6 ± 3.5-16.3 ± 9.4 mm, P < .001) patients. MLBS progression was greater in shunted patients (P = .001). Shunts with higher VOPs did not increase MLBS relative to nonshunted patients (P = .834), whereas MLBS increased with lower VOPs (P = .001). Severe MLBS was associated with debilitating headaches (P = .048).

Conclusion: Patients undergoing hemispheric surgery often develop postoperative MLBS, ie, exacerbated by CSF shunting of the ipsilateral surgical cavity, specifically when using lower VOP settings. MLBS exacerbation may be related to overshunting. Severe MLBS is associated with debilitating headaches.

FIGURE 1.

MRI and CT scans demonstrating MLBS quantification in nonshunted and shunted patients. The biparietal diameter (yellow line) is divided by 2 and subtracted from the ipsilateral distance from the inner table to the septum pellucidum (blue line). A, Preoperative axial turbo spin echo (TES) T2-weighted MRI of the pediatric patient with history of medically intractable epilepsy secondary to left perinatal middle cerebral artery stroke demonstrating a baseline MLBS of 0.51 cm. B, Postoperative axial TSE T2-weighted MRI of the patient from A at 6 months after functional hemispherectomy demonstrating a MLBS of 1.04 cm. C, Preoperative axial TSE T2-weighted MRI of the pediatric patient with history of medically refractory infantile spasm demonstrating a baseline MLBS of 0.14 cm. D, Postoperative, noncontrast enhanced axial CT of the patient from C after functional hemispherectomy and subsequent early cerebrospinal fluid shunting secondary to PHH demonstrating a MLBS of 0.04 cm. E, Surveillance axial TSE T2-weighted MRI of the patient from C and D at a 72-month follow-up with a MLBS of 2.41 cm. CSF, cerebrospinal fluid; CT, computed tomography; MLBS, midline brain shift; TSE, turbo spin echo.

FIGURE 2.

Natural progression of MLBS in nonshunted and shunted patients. MLBS significantly increased between the first and last follow-up for nonshunted and shunted patients according to the paired samples t-test.*P < .05, **P < .01, and ***P < .001. MLBS, midline brain shift; NS, no significance.

FIGURE 3.

Comparison of MLBS in nonshunted, shunted with higher VOP, and shunted with lower VOP patients posthemispheric surgery and at last follow-up. No statistical difference was observed between nonshunted and shunted with higher VOP patients at last follow-up, whereas shunted with lower VOP patients had significantly greater MLBS than nonshunted patients according to analysis of covariance. **P < .01. MLBS, midline brain shift; NS, no significance; OP, opening pressure; VOP, valve opening pressure.