Surgical Decompression and Stabilization for Lumbar Lesions: Osteomyelitis and Tumors




Overview


Surgical management of neoplastic and infectious lesions of the lumbar spine involves extensive preoperative planning to ensure proper patient selection and operative approach. Despite the differences in patient selection criteria, preoperative workup, and adjuvant treatments, the choice of operative approach for either an infectious or neoplastic lesion of the lumbar spine is often the same.


Infection of the lumbar spine is more often than not a nonsurgical disease. Patients with osteomyelitis and/or diskitis can usually be treated nonoperatively with antibiotics. When the organism in question is unknown, body fluid cultures are obtained; if results are negative, a biopsy guided by computed tomography (CT) can often obviate the need for open intervention. Indications for surgical intervention include 1) compression of the conus medullaris or nerve roots, causing neurologic deficits; 2) lesional involvement of at least two spinal columns; 3) significant (≥25 degrees) kyphotic deformity; 4) failure of medical therapy to cure the infection and radiologic evidence of persistent spinal disease; 5) failure to identify the organism causing the infection; and 6) intractable pain secondary to mechanical instability or ongoing infection.


Neoplasms in the lumbar spine can be divided into primary lesions or secondary metastases . Metastases are by far the most common tumors of the lumbar spine, although the vast majority of symptomatic spinal metastases occur in the thoracic spine. Most spinal metastases originate from and involve the vertebral body; only rarely do they solely affect the posterior spinal elements. Lung, breast, and prostate cancer are the most common metastatic tumors found in the spine. Other secondary tumors often seen include lymphoma, renal cell carcinoma, and multiple myeloma. Surgery is indicated for patients with tumor causing progressive neurologic deterioration, spinal instability, or significant deformity. It is also indicated when the tumor type is unknown, or when it is known but is radiation resistant.


Surgery for metastatic disease is often palliative, but it can help maintain or improve neurologic function in affected patients. It is often supplemented with radiation therapy in the form of radiosurgery. In patients who have primary tumors of the lumbar spine, it is possible to achieve a cure through en bloc resection of the neoplasm when technically feasible. Depending on the extent of tumor involvement, surgery may entail a complete spondylectomy or resection of only a portion of the involved bone.




Preoperative Preparation


In patients with either tumor or infection of the lumbar spine, proper preoperative laboratory and radiologic diagnostic tests must be run for surgical intervention to take place. For both pathologies, magnetic resonance imaging (MRI) of the lumbar spine, both with and without contrast, is ideal to visualize the pathology in question and to discern any involvement of adjacent tissues; CT of the lumbar spine is useful to determine bony quality. In cases of infection and neoplasm, the degree of bone destruction helps dictate the extent of instrumentation needed.


Patients with osteomyelitis often have adjacent involvement of the disks and/or end plates. This can help to radiologically differentiate between infection and neoplasm when the diagnosis is in question, because tumor typically does not affect the end plates and disks. Epidural abscesses are sometimes associated with osteomyelitis. If present, the abscess is usually anterior to the thecal sac. Although patients with anterior pathology often require anterior approaches, it is often possible to approach anterior epidural abscess through a posterior approach with retraction of the thecal sac and nerve roots.


In patients with suspected neoplasm, a systemic workup and imaging survey is indicated to help determine whether the pathology is metastatic. CT of the chest, abdomen, and pelvis should be performed in these patients, with and without contrast. If any lesions are identified on imaging anywhere in the body other than the spine, and these are technically accessible using CT-guided biopsy, they should be targeted to obtain tissue for diagnosis before open surgical intervention. Knowing the type of tumor will help determine whether surgery, radiation, or chemotherapy will be the best treatment. In patients with metastatic spine lesions, surgery is often palliative and is usually reserved for single-level or multiple, contiguous-level tumor involvement causing compression of neurologic elements. Surgical resection of the tumor with supplemental instrumentation can improve overall patient neurologic function and quality of life.


Patients with osteomyelitis are usually treated with antibiotics, either alone or in combination with surgery. In patients who require surgical intervention but do not have an identified offending organism, it is important that antibiotics be withheld before surgery; intraoperative cultures can be negative if the patient has been receiving antibiotics. After cultures have been obtained, empiric antibiotics can be administered until pathogen speciation is completed. In patients with osteomyelitis or neoplasm, treatment by a multidisciplinary team that includes infectious disease specialists or oncology/radiation specialists is important as part of a comprehensive treatment plan.




Posterior Approaches


Laminectomy


Although rare, tumor and infection can arise solely in the posterior elements of the vertebrae. If confined to the laminae and facets, tumor can often be resected from a posterior approach. In these cases, patients are placed prone on a Jackson table with the patient’s arms outstretched above the head superiorly. Following fluoroscopic localization of the involved level, a midline incision is centered at the level of the pathology and is carried down through the subcutaneous tissues to the dorsal lumbosacral fascia. A midline incision is made through the fascia down to the spinous process, and subperiosteal dissection is carried out using monopolar cautery and Cobb retractors. Care must be taken to avoid excessive muscle retraction laterally, because this can cause injury to the dorsal ramus of the spinal nerve, which can potentially lead to spinal muscle atrophy. By staying in the subperiosteal plane, bleeding is minimized. Dissection is carried laterally to the extent needed, out to the transverse processes if necessary. Depending on the extent of tumor involvement, either a standard laminectomy or some variant thereof can then be performed using a high-speed drill, rongeurs, curettes, and Kerrison punches ( Fig. 40-1 ). Any surrounding soft-tissue mass can be removed at the same time. If involvement of the facet joints is extensive, posterolateral instrumentation and fusion are performed. In the case of epidural abscess causing nerve root or thecal sac compression, a hemilaminectomy often allows sufficient access for evacuation of the abscess.




Figure 40-1


Illustration shows the resection of a tumor that involves the posterior elements at L3. After a standard midline approach to the lumbar spine, the involved spinous process, lamina, pedicles and facets are removed en bloc.


Lateral Transpedicular-Extracavitary Approach


The transpedicular-extracavitary approach (TECA) to the lumbar spine allows access to the posterolateral and anterolateral aspects of the thecal sac and to the vertebral body, in case a corpectomy is planned. Special attention is required when approaching the L4 or L5 levels; this usually requires dissection of the lumbar plexus off the iliopsoas muscle, and it risks injury to important nerves. This approach is an alternative to the retroperitoneal approaches and does not require an abdominal or flank incision. Approaching posteriorly through this avenue allows decompression of the thecal sac, corpectomy, and both anterior and posterior instrumentation (360-degree stabilization). All of this can be performed through one incision and in one sitting. This approach also allows a greater lateral exposure, which can be especially useful in the case of tumor extension into the paraspinal soft tissues.


The patient is placed prone on a Jackson table or on chest and hip bolsters with outstretched arms. A midline incision is made that extends two to three levels above and below the level of interest. Dissection is carried down through the subcutaneous tissues to the dorsal fascia. A midline incision is made through the fascia down to the spinous process, and subperiosteal dissection is carried out using monopolar cautery and Cobb retractors. Dissection is carried laterally to expose the transverse processes ( Fig. 40-2 ). Then, laminectomies are performed over the level of interest and at least one level above and below.




Figure 40-2


Exposure of the spinous process, lamina, and transverse process during the initial stage of a transpedicular approach.


After decompressing the thecal sac, pedicle screws are placed at the levels above and below the vertebrectomy site to encompass at least three segments above and below. To include three segments below the vertebrectomy, the instrumentation may need to be extended to include the ilium. Once pedicle screws are placed, the process of vertebrectomy is begun.


First, bone and ligament removal is extended laterally at the intended level. The superior facet, inferior facet, pars interarticularis, and transverse processes of the vertebrae to be resected are removed. After removal of the posterior elements, the ipsilateral pedicle is visible, as are the nerve roots. It should be noted that bleeding can be substantial at this point; bipolar electrocautery and hemostatic agents should be used generously to minimize bleeding. Using a high-speed burr, the pedicle is drilled down to the vertebral body such that a small rim of cortical bone remains. Using an up-angled curette, the remaining wall of the pedicle is broken away from the thecal sac and removed. Attention is paid to the exiting nerve root to minimize injury.


A systematic approach is critical to ensure a safely performed corpectomy. First, drilling is begun ventral to the thecal sac in a lateral to medial manner to create a small working space within which Kerrison rongeurs and curettes can be used to resect the posterior wall of the vertebral body and the posterior longitudinal ligament (PLL). Removal of the ipsilateral vertebral body occurs first. This allows direct access to the contralateral vertebral body and minimizes the degree of thecal sac retraction required to do so. Thrombin-soaked Gelfoam is packed into the vertebral body to control bleeding. Placement of a small, temporary rod before corpectomy can reduce the likelihood of spinal translation while the remainder of the anterior column is resected.


Following resection of the vertebral body, the intervertebral disks above and below the corpectomy site are resected. The upper disk is easily accessible, because it is situated immediately above the resected pedicle. The inferior disk is more difficult to resect, because the nerve root below the resected pedicle interferes with wide exposure at the inferior aspect of the vertebral body. The nerve root is carefully manipulated and is protected using a nerve root retractor. If the corpectomy is performed to resect tumor, it is imperative to use microinstrumentation, such as nerve microhooks and forceps with teeth; these are used to explore the dura-tumor interface and to resect tumor off the dura before resection of the posterior wall of the vertebral body and PLL.


Once the corpectomy has been performed, and neural elements are decompressed, the end plates are then decorticated and an interbody device is carefully placed. It is sometimes easier to place an expandable cage into the space, because the lumbar nerve roots can make placement of larger constructs difficult, and this can increase the potential for nerve root injury. Another option is insertion of a chest tube filled with poly-methylmethacrylate (PMMA; Fig. 40-3 ).


Jul 11, 2019 | Posted by in NEUROSURGERY | Comments Off on Surgical Decompression and Stabilization for Lumbar Lesions: Osteomyelitis and Tumors

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