Posterior Minimally Invasive Procedures to Spine Tumors

Published on 02/04/2015 by admin

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Last modified 02/04/2015

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Chapter 31 Posterior Minimally Invasive Procedures to Spine Tumors

VERTEBROPLASTY TECHNIQUE

TRANSPEDICULAR APPROACH

Under fluoroscopic assessment, a 10- to 15-gauge 10- to 15-cm length needle, preferentially with a beveled cutting tip, is inserted along the selected pedicle (Fig. 31-1).1 Within the pedicle, the bevel of the needle is oriented medially (the tip of the needle pointing laterally) to avoid the spinal canal. Once within the vertebral body, the bevel is rotated to face laterally (the tip of the needle pointing medially), directing the needle medially, toward the midline. The most desirable position of the needle tip is the anterior third of the vertebral body near the anteroposterior midline (Fig. 31-2). When dealing with a vertebra plana, a more lateral position of the needle is desired. If the underlying pathological condition remains uncertain before the cement injection, a bone biopsy specimen can be obtained using a 15- to 18-gauge biopsy needle placed through the vertebroplasty (VP) needle. Then vertebral venography is performed to evaluate the flow dynamics. When a high-flow, hypervascular pattern is observed, the reposition of the needle tip may be required to perform an embolization of the venous channels, either with alcohol, N-butyl-2-cyanoacrylate (Histoacryl), Gelfoam, plugs, or Avitene powder before cement injection. After the powder and a liquid component are mixed and the desired consistency is reached, the polymethyl methacrylate (PMMA) is injected through the needle. The injection is continued until resistance is met, or the cement reaches the posterior wall of the vertebral body, or a desired result is achieved. The injection should be stopped if epidural, foraminal, or venous leakage is detected.

CASE ILLUSTRATION

A 45-year-old woman with breast cancer was treated with VP at C3 metastasis (Fig. 31-4). The approach was performed from the left side, with finger compression of the visceral tissue. During VP, esophagography should be performed to check the esophageal injury. Bone cement of 2cc was injected to the compressed C3 body. A small amount of bone cement was seen to leak into the paraspinal space. Preoperative neck pain was much improved after VP.

BIOMECHANICS: VOLUME OF BONE CEMENT

The effective volume of bone cement is estimated to be from 3 to 10cc; however, a study on the effects of bone cement volume and distribution on vertebral stiffness after VP showed that 14% filling or 3.5cc was necessary to restore stiffness of the damaged vertebral body to the pre-damaged value at the lumbar level.2 This result suggests that large fill volume may not be the most biomechanically optimal configuration, and an improvement might be achieved by use of a lower cement volume with symmetrical placement. Also, with the unipedicular approach, the stiffness comparable to the intact body can be achieved in cases of symmetrical distribution of bone cement.

COMPLICATIONS

The complication rate in VP for malignant disease is higher than that in osteoporosis: an estimated 10% compared with 1–2% in osteoporosis patients. Hypotension resulting from absorption of the PMMA monomer can be shown. Hence, blood pressure should be monitored during the procedure. Exothermic reaction of adjacent structures can occur theoretically. However, the protective effect of dura and cerebrospinal fluid lessens the significant cord damage caused by thermal injury. The major problems are pulmonary embolism and neurological complication.

Pulmonary Embolism

Pulmonary embolism may occur during the VP. Bone cement leaked from the vertebral body via the venous channel can enter the systemic circulation. It may be filtered in the pulmonary circulation system (Fig. 31-5). Even though pulmonary embolism does occur, most patients may be asymptomatic. If symptomatic, patients complain of tachypnea and respiratory difficulty. Tachycardia is monitored. The incidence of pulmonary embolism is 3–4%.3 Most patients can be treated with anticoagulant therapy and respond favorably.4

SPECIAL PROBLEMS OF VERTEBROPLASTY IN CANCER PATIENTS

Injection into the Tumor Mass

The injection of the cement into dense tumor mass tissue may be more difficult than in an osteoporotic spine, and the PMMA pattern may appear spotty and discontinuous.5 To provide maximum structural support, both the osteolytic portion of the vertebral body and the seemingly normal bone should be injected. Vascular tumors, such as renal cell cancer metastasis, may show frank arterial flow through the cannula once the stylet is removed. Hence, the trajectory track should be packed with PMMA to prevent excessive bleeding.

PARASPINAL TECHNIQUE: LUMBAR SPINE

Entry Point

At the upper lumbar spine (L1 and L2), the entry point is just medial to the 12th rib. The midline and a line bisecting the transverse process and pedicle are identified (Fig. 31-10). The entry point is on the bisecting line and is 5mm medial to the 12th rib. The 12th rib is confirmed with fluoroscopy or palpitation of the rib. At lower lumbar spine (L3–5), a line bisecting the transverse process and pedicle is drawn. The entry point is located on the line, approximately 6–10cm away from the pedicle.

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