| ABSTRACT: |
To define the time course and mechanism of enhancement
of epidural fibrosis after gadolinium-DTPA (Gd-DTPA) injection, we undertook
a three-part study in humans and dogs with epidural scar after spine surgery.
First, the dynamic in vivo contrast-enhancing properties of epidural scar
were assessed by using sequential fast (18-sec) spin-echo sequences after
contrast injection. Epidural scar in dogs rapidly enhanced; peak enhancement
(101%) was 6 min after injection, with a slower decline toward baseline
to 45% after 44 min. Epidural fibrosis in patients followed a similar pattern,
with a maximum enhancement of 73% after 5 min. Paraspinal muscle had a lower
peak enhancement in both patients (36%) and dogs (22%). Second, vascular
injection in two dogs with India ink demonstrated multiple small vessels
throughout the epidural scar. Third, light and electron microscopy was performed
on epidural scar obtained at reoperation in both patients and dogs. Light
microscopy showed multiple small capillaries scattered throughout a background
of collagen. Electron microscopy demonstrated a wide variation in the junctions
between endothelial cells ranging from "tight" to "loose."
Regions of endothelial discontinuity were also visualized. This study suggests
that Gd-DTPA diffuses rapidly into the extravascular space in epidural scar,
with a slower, net movement toward the intravascular compartment as the
agent is renally filtered. The contrast agent transgresses the endothelium
through "leaky" intercellular junctions and areas of endothelial
discontinuity. |