Spinal Compliance Curves: Preliminary Experience with a New Tool for Evaluating Suspected CSF Venous Fistulas on CT Myelography in Patients with Spontaneous Intracranial Hypotension

Abstract

Background and purpose: Craniospinal space compliance reflects the distensibility of the spinal and intracranial CSF spaces as a system. Craniospinal space compliance has been studied in intracranial pathologies, but data are limited in assessing it in spinal CSF leak. This study describes a method to estimate craniospinal space compliance using saline infusion during CT myelography and explores the use of craniospinal space compliance and pressure-volume curves in patients with suspected cerebrospinal-venous fistula.

Materials and methods: Patients with suspected cerebrospinal-venous fistula underwent dynamic CT myelography. During the procedure, 1- to 5-mL boluses of saline were infused, and incremental changes in CSF pressure were recorded. These data were used to plot craniospinal space compliance curves. We calculated 3 quantitative craniospinal space compliance parameters: overall compliance, compliance at opening pressure, and the pressure volume index. These variables were compared between patients with confirmed cerebrospinal-venous fistula and those with no confirmed source of CSF leak.

Results: Thirty-four CT myelograms in 22 patients were analyzed. Eight of 22 (36.4%) patients had confirmed cerebrospinal-venous fistulas. Bolus infusion was well-tolerated with no complications and transient headache in 2/34 (5.8%). Patients with confirmed cerebrospinal-venous fistulas had higher compliance at opening pressure and overall compliance (2.6 versus 1.8 mL/cm H₂0, P < .01). There was no difference in the pressure volume index (77.5 versus 54.3 mL, P = .13) between groups.

Conclusions: A method of deriving craniospinal space compliance curves using saline intrathecal infusion is described. Preliminary analysis of craniospinal space compliance curves provides qualitative and quantitative information about pressure-volume dynamics and may serve as a diagnostic tool in patients with known or suspected cerebrospinal-venous fistulas.

FIG 1.

Sample craniospinal compliance curves in a 51-year-old man confirmed to have CVF at operation. Combined plot of 2 CTMs with dashed lines showing a linear approximation of compliance (A). Initial nondiagnostic CTM (B) shows a roughly sigmoid pattern with an inflection point seen after a ∼15-mL normal saline bolus was administered (black curved arrow). Repeat CTM with more aggressive positive-pressure augmentation shows an abrupt loss of pressure (purple arrows) after infusion volume of 27 mL of normal saline (C). The CVF became apparent only after pressure was increased beyond this threshold point.

FIG 2.

A craniospinal compliance curve in a 70-year-old woman with confirmed CVF (A) shows high compliance (ie, smaller change in pressure per increase in volume) with multiple abrupt pressure drops (arrows) above 10 cm H₂0. Recent brain MR imaging shows characteristic features of SIH (B), including reduced mamillopontine distance, low cerebellar tonsils, and pachymeningeal enhancement. A right T7–8 CVF was identified on decubitus CT myelography (C and D). Hyperdensity of the paraspinal vein and azygous vein (dashed circle) aids in identification of the fistula (white arrows). The patient was treated with percutaneous fibrin glue injection.

FIG 3.

Craniospinal compliance curve in a 63-year-old woman suspected but not radiographically confirmed to have CVF. Estimated linear compliance for each CTM is shown as a dashed line, approximating the shape of the pressure-volume curve (A). The second CTM was performed after the blood patch showed an increase in opening pressure (B and C). The effect of the blood patch is diminished on delayed repeat CTM (D), in which the left side of the curve, including opening pressure, more closely matches the prepatch curve.

FIG 4.

Schematic of the components of craniospinal compliance and hypothesized physiology of CVF (CSF = green, arterial blood = red, venous blood = blue). A normal CSC encompasses both intraventricular and subarachnoid CSF and is defined by cranial and spinal compartments (larger and smaller boxes, respectively) as well as the arteriovenous vascular bed (A). In dural tear CSF leak or CVF at low pressure, an equilibrium state (B) may exist in which the leak is occult by CTM. With special maneuvers (dynamic CTM, respiratory-phase variation, jugular pressure, and bolus-pressure augmentation), pressure gradients may open the leak, allowing detection on CTM (C).