Third ventricular shape: a predictor of endoscopic third ventriculostomy success in pediatric patients

Clinical article

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Object

The criteria for identifying patients in whom endoscopic third ventriculostomy (ETV) provides control of hydrocephalus remain in evolution. In particular, it is not clear when ETV would be effective if intraventricular obstruction is not found preoperatively. The authors postulated that 1) displacement of the third ventricle floor inferiorly into the interpeduncular cistern and displacement of the lamina terminalis anteriorly into the lamina terminalis cistern could predict clinical success of ETV, and 2) improvement in these displacements would correlate with the success of ETV.

Methods

Magnetic resonance imaging in 38 consecutive patients treated between 2004 and 2010 was reviewed to assess displacement of the lamina terminalis and third ventricular floor prior to and following ETV. Displacements of the floor and lamina terminalis were judged qualitatively and quantitatively, using a newly created index, the Third Ventricular Morphology Index (TVMI). The association between the aforementioned morphological features and clinical success of ETV was analyzed.

Results

Ninety-six percent of patients in whom the authors preoperatively observed displacement of the lamina terminalis and the third ventricular floor were successfully treated with ETV. Displacements of the third ventricular floor and lamina terminalis, as judged qualitatively, correlated with the clinical success of ETV. The TVMI correlated with the qualitative assessments of displacement. Postoperative decrease in the TVMI occurred in the majority of successfully treated patients. Changes in third ventricular morphology preceded changes in other measures of third and lateral ventricular volume following ETV.

Conclusions

Assessment of third ventricular floor and lamina terminalis morphology is useful in predicting clinical success of ETV and in the follow-up in treated patients. The TVMI provided a quantitative assessment of the third ventricular morphology, which may be useful in equivocal cases and in research studies.

Abbreviations used in this paper: ETV = endoscopic third ventriculostomy; FOHR; frontal and occipital horn ratio; TVI = Third Ventricle Index; TVMI = Third Ventricular Morphology Index; VP = ventriculoperitoneal.

Article Information

Address correspondence to: D. Douglas Cochrane, M.D., F.R.C.S.C., Division of Neurosurgery, Department of Surgery, University of British Columbia, Division of Neurosurgery, Department of Pediatric Surgery, British Columbia Children's Hospital, 4480 Oak Street, Vancouver, British Columbia, Canada V6H 3V4. email: dcochrane@cw.bc.ca.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Sagittal preoperative image demonstrating how to determine the qualitative third ventricular wall displacement. For the lamina terminalis, displacement was judged by the convex displacement of the lamina into the lamina terminalis cistern from a dotted line drawn from the chiasm to the anterior commissure (arrow, a). Third ventricular floor displacement (b) was assessed by noting the displacement of the floor from a dotted line drawn from the chiasm to the mammillary bodies (arrow, b).

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    Sagittal preoperative (A), sagittal postoperative (B), and axial (C) T2-weighted MR images demonstrating how to measure the TVMI. a = distance from mammillary body to point of maximal displacement of lamina terminalis; b = distance from anterior commissure to point of lowest displacement of third ventricular floor; BPD = biparietal diameter.

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    Preoperative and postoperative images of patients treated successfully with ETV. Preoperative images show the “omega” (ω) shape of the anterior third ventricle. Postoperative images show resolution of deformation with restoration of a normal W-shaped configuration. A: No apparent intraventricular obstruction visualized. Preoperative convexity of the lamina terminalis and third ventricular floor and postoperative resolution of the deformation with flow void postoperative. B: Aqueduct obstruction. Preoperative deformity of the lamina terminalis and floor and postoperative resolution of deformity with flow void. C: Midbrain and thalamic tumor. Preoperatively the lamina is not deformed but the floor is draped over the dorsum sella; postoperatively the floor is elevated and the ventriculostomy visible. The lamina is normally aligned, and there is no flow void. D: Dorsal aqueduct obstruction due to mass. The floor and lamina deformed, creating the ω shape. Postoperatively the deformation is resolved, and the floor and lamina take on the shape of a W.

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    Initial (A and B) and repeat (C and D) ETV was performed in infant without intraventricular obstruction on imaging. The initial ETV successfully resolved a third ventricular wall deformity; flow void seen. It failed 3 months later. The repeat ETV was clinically successful with flat floor and flow void. Residual lamina terminalis deformity persisted to time of last imaging.

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    Failed ETV in patient with no evidence of intraventricular or cisternal obstruction. Left: The third ventricular floor is flat and the lamina terminalis exhibits a convexity. Right: The ETV was performed with successful creation of flow void and no change in the position of the floor or lamina. As the head circumference continued to increase, a VP shunt was placed.

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    Patients without significant deformity of the lamina terminalis and/or floor of the third ventricle. A: Infant with myelomeningocele. Preoperatively the floor is flat as is the lamina terminalis. Postoperatively there is a flow void and no change in the third ventricular walls. The patient did not undergo shunt placement. B. Dorsal midbrain tumor, repeat ETV. The floor is flat with some laminar deformity. The ventriculostomy was found to be patent at operation. Widening the ventriculostomy resulted in no change other than improvement in flow void. C. Infant with no intraventricular obstruction and with flat or bowed-up floor and nondisplaced lamina. Postoperatively there is no flow void and the floor is concave. The ETV was deemed to have failed and a VP shunt was placed. D. Posttraumatic hydrocephalus in a patient with craniocervical dislocation. Preoperatively the floor is flat and the lamina is minimally displaced. Postoperatively there was normalization of ventricular walls and a flow void, and hydrocephalus resolved subsequently.

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    Graphs showing the association of TVMI with deformational variables. The preoperative ranges of TVMI values reflect, with minimal overlap, the presence or absence of convexity as seen on imaging.

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    Graph demonstrating change in the TVMI stratified for clinical success and failure. With three exceptions (two primary and one repeat procedure), all clinically successful ETVs showed a decrease in the TVMI. With one exception, failures requiring shunting showed either no such change or an increase in the index post-ETV.

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