11.9\ Percutaneous Spine

Treatments

11.9.1\ Vertebral Augmentation

11.9.1.1\ Discussion

Kyphoplasty and vertebroplasty are percutaneous interventions that have been used to treat a variety of conditions including of osteoporotic vertebral compression fractures, certain spine tumors, and selected traumatic fractures. Vertebroplasty consists of injecting polymethylmethacrylate cement into the affected vertebral body, while kyphoplasty involves the use of a balloon that is first inflated in the vertebral body and then deflated prior to cement injection. Skyphoplasty is another cement vertebral augmentation technique that is no longer implemented. The procedure involves the use of SKy bone expander (Disc Orthopaedic Technology/ Disc-O-Tech, Monroe Township, New Jersey), which enlarges like an accordion into a popcornlike crenulated configuration. Compared with kyphoplasty device, skyphoplasty generates higher pressures, expands more predictably, requires a larger cannula, and cannot be repositioned once it is deployed.

The imaging features for vertebroplasty and kyphoplasty are similar: cement should be confined to the intramedullary space of the vertebral body with disruption and compaction of the trabeculae (Fig. 11.125). However, the cement deposits from vertebroplasty tend to have a more diffuse and granular appearance, while cement deposits from kyphoplasty tend to be more localized and globular, filling the cavity produced by balloon dilatation. A small increase in vertebral body height is sometimes observed following vertebral augmentation (Fig. 11.126). The cement is hyperattenuating on radiographs and CT and very low signal intensity on all MRI sequences. Skyphoplasty produces the characteristic configuration of cement deposition that is often present on post-procedure imaging (Fig. 11.127).

During vertebral augmentation, cement can leak outside of the vertebral body and into the

neural foramen and spinal canal (Figs. 11.128, 11.129, and 11.130), which can result in neurological deficits and predisposes to degenerative spondylosis. Overall, this type of complication occurs in 30–75% of cases, whether or not an intravertebral cleft exist. The heat generated from the exothermic reaction as the cement hardens can burn the spinal cord or nerve roots. However, significant neurological symptoms result in only a minority of cases. In addition, if there is preexisting spinal canal stenosis and the amount of cement is large, extravasation can be a major complication of vertebroplasty or kyphoplasty. Radiographs and CT can readily depict the hyperattenuating cement extending outside the vertebral body. MRI or CT myelography are useful for evaluating whether the cement impinges upon the spinal cord and nerve roots.

Cement embolization to the pulmonary arteries occurs in 4.6–6.8% of cases of ­kyphoplasty/ vertebroplasty. Leakage of cement into the paravertebral veins is a strong risk factor for cement embolization to the lungs. Underlying multiple myeloma may also be a risk factor. However, the incidence of this complication is the same for kyphoplasty as for vertebroplasty. On chest imaging, pulmonary artery cement emboli characteristically appear as high attenuation tubular or branching structures in the distribution of the pulmonary arteries (Fig. 11.131). The cement fragments can range widely in size, and small fragments are most readily identified on non-con- trast CT.

The incidence of new compression fractures following vertebroplasty or kyphoplasty ranges from 5% in patients with idiopathic osteoporosis and up to about 45% in patients with steroid induced or secondary osteoporosis. Over two-­ thirds of new fractures occur in the adjacent vertebral body and present within 3 months of the procedure (Fig. 11.132). Extrusion of cement into the disc space appears to increase the risk for adjacent vertebral body fracture, likely as a result of altered biomechanics. Other factors associated with adjacent vertebral body fracture include a thoracolumbar junction location and greater height restoration.

Fig. 11.125  Kyphoplasty and vertebroplasty. Sagittal CT image shows the granular deposits of vertebroplasty cement and the more globular deposits of cement from kyphoplasty, all of which are confined to the vertebral bodies

Fig. 11.127  Skyphoplasty. Axial CT image shows cement with characteristic lobulated margins in the vertebral body (encircled). There is also cement in the cannula insertion path across the left pedicle

Fig. 11.126  Increased vertebral body height after vertebral augmentation. Initial sagittal T2-weighted MRI (a) shows a thoracic compression fracture. Sagittal

T2-weighted MRI after vertebral augmentation (b) shows interval elevation of the superior endplate of the treated vertebral body (arrow)

Fig. 11.128  Neural foramen cement leakage. Sagittal CT image of the lumbar spine shows cement within filling a neural foramen (arrow)

Fig. 11.129  Disc space and spinal canal cement leakage. Sagittal CT image shows cement extending into the adjacent intervertebral disc spaces, even extending into the spinal canal (arrow)

Fig. 11.130  Degenerative disc disease related to cement extravasation. Prevertebroplasty lateral radiograph (a) shows a thoracic vertebral compression fracture. Post-­ vertebroplasty lateral radiograph (b) shows cement within

the adjacent disc space and interval development of endplate sclerosis, worsening kyphosis and formation of a bridging osteophyte (arrow)

Fig. 11.131  Cement intravasation and pulmonary embolism. The patient has a history of multiple myeloma with compression fractures, for which the patient was treated with vertebral augmentation in the thoracic spine. After the procedure, the patient experienced shortness of breath.

Axial CT image (a) shows the presence of pulmonary artery cement embolism (arrow). Axial CT image at another level (b) shows intravasation of cement into the left paravertebral veins (encircled)

Fig. 11.132  Adjacent vertebral body fracture. The patient has a history of osteoporosis and presented with new pain 3 weeks after L2 kyphoplasty. Initial sagittal T1-weighted MRI (a) shows an acute compression fracture of the L2, but the L1 vertebral body is normal at this

time. T1-weighted MRI after kyphoplasty (b) show cement in the L2 and an acute L1 vertebral body compression fracture as evidenced by edema and mild loss of height (arrow)