To the Editor:—
Thoracic epidural catheterization was implemented in a 62-yr-old woman scheduled for subtotal gastrectomy. A FlexTip Plus® epidural catheter (single end hole; Arrow International, Reading, PA) was inserted at the T9–T10 intervertebral space and directed cephalad for 5 cm. With the patient's consent, a 10-cm slab of a thin-cut spiral computed tomography (CT) scan was obtained through T6–T12 with 1-mm collimation at a pitch of 2,140 kVp and 160 mA and with a 13-cm field of view (HiSpeed Advantage scanner; GE Medical Systems, Milwaukee, WI).
The raw data were processed with a 0.5-mm overlap using the GE Advantage workstation (DentaScan, GE Medical Systems). The axial transverse section of the CT image demonstrated the existence of a catheter in the epidural space (fig. 1A). With an oblique view, the path of the catheter in the epidural space was displayed with multiplanar reconstruction (fig. 1B) or a three-dimensional surface-shaded display (fig. 2). There was no kinking or knotting of the catheter despite the curved path in the epidural space.
A substantial incidence of failed or unilateral epidural block may be due to the complexity of the epidural space. 1When looping, kinking, entrapment, or knotting of epidural catheters occurs, it is not easy to visualize the path of the radiopaque catheter within the epidural space. 2,3Although conventional radiography, 4,5ultrasonographic imaging, 6epidurography with contrast medium, 7CT, 8–10or magnetic resonance imaging 11might be useful, a potential allergic reaction to contrast medium, interference with metal coils, or blockade or occlusion of the epidural catheter could still be problematic. Thin-cut volumetric CT scanning, coupled with two-dimensional multiplanar or three-dimensional model reconstruction, has been used for evaluation of the upper airway anatomy. 12
Given the exquisite tissue contrast of CT in displaying the epidural space, its potential in the evaluation of a problematic epidural catheter has never been explored. An axial scan shows the exact location of the catheter in the epidural space and thus is useful in detecting malposition. With two-dimensional multiplanar and three-dimensional surface display models, the course of the catheter in the epidural space is depicted. In conclusion, three-dimensional CT imaging appears to be a novel tool to visualize the position and path of an epidural catheter.