Percutaneous translumbar spinal cord compression injury in a dog model that uses angioplasty balloons: MR imaging and histopathologic findings

Abstract

Background and purpose: Previous animal models for spinal cord injury required laminectomy and exposure of the spinal cord to create direct trauma, compromising imaging by both surgical artifact and the nature of the production of the injury. Our purpose was to study a model that uses percutaneous intraspinal navigation with an angioplasty balloon, providing a controlled degree of spinal cord compression and allowing improved MR imaging of spinal cord injury.

Methods: Nine mongrel dogs were studied. MR images were obtained of six dogs after technique development in three dogs. Angioplasty balloons measuring 7 or 4 mm in diameter and 2 cm in length were placed in the midthoracic subarachnoid space. Imaging was performed by using a 1.5-T MR imaging unit before and after balloon inflation. The balloon was inflated within 5 seconds and deflated after 30 minutes. T1- and T2-weighted and contrast-enhanced images were acquired. Spinal cords were submitted for pathologic examination.

Results: All four animals with 7-mm balloons experienced hemorrhage, and three had axonal injury revealed by histopathologic examination. One of two animals with 4-mm balloons experienced no injury, and one had axonal injury without hemorrhage. Regional parenchymal enhancement was seen in two of the animals with 7-mm balloons.

Conclusion: This percutaneous spinal cord injury model results in a graduating degree of injury. It differs from previous techniques by avoiding surgical exposure and the associated artifacts, yet it offers histopathologic findings similar to those of human spinal cord injury. The canine spinal cord is amenable to MR imaging with clinical imaging units. Further evaluations with various durations of compression and various balloon sizes are warranted.

Fig 1.

Images from a pilot study. After induction of general endotracheal anesthesia, the lumbar subarachnoid space was entered with a needle. A guidewire was introduced via the needle and directed cephalad; then, the needle was withdrawn, and the guidewire was used for coaxial advancement of the angioplasty balloon, mimicking the method used in vascular access for angiography. A, Guidewire introduced via neural foramen (lateral approach) and ascending in spinal canal. B, Angioplasty balloon introduced over guidewire. Proximal and distal markers on balloon are shown by arrows. C, Example of an MR image of a 7-mm balloon (black arrow) inflated against the compressed spinal cord in animal 2 (white arrow).

Fig 2.

Images of animal 4. A, Example of hematoxylin and eosin staining obtained at the level of the balloon. Multiple regions of petechial hemorrhage are indicated by arrows. Petechial hemorrhage is a characteristic of spinal cord contusion. B, Beta amyloid precursor protein immunostaining of the region shown in A. Amyloid precursor protein is synthesized in neurons in the CNS and peripheral nervous system and is transported to the nerve endings from the cell body. Amyloid precursor protein accumulates when axoplasmic flow is disrupted; it is therefore a sensitive marker of axonal injury. Regions of stain accumulation (arrows) indicate posterior axonal injury.

Fig 3.

Images of animal 3. A, Example of axial view T2-weighted MR image obtained at the level of balloon inflation after the balloon was deflated and removed. The cord displays homogenous signal intensity with no signal intensity change in the dorsal region that shows contrast enhancement in C. B, Unenhanced T1-weighted MR image obtained in the axial plane at the level of balloon inflation. No abnormal signal intensity is seen in the spinal cord. C, Contrast-enhanced T1-weighted MR image of the region shown in B. A large region of enhancement is located at the dorsal region of the spinal cord (arrow). D, Unenhanced sagittal view T1-weighted MR image of the region shown in B. Note that no abnormal signal intensity is seen in the spinal cord. E, Focal enhancement is observed after the injection of contrast material (arrow). F, Hematoxylin and eosin staining of the spinal cord shows parenchymal hemorrhage in the peripheral white matter (arrows). G, Beta amyloid precursor protein immunostaining of the region shown in B highlights well-developed axonal swellings (stain accumulation) in the cross section (arrow).