Spinal tumours can arise from any of the hard or soft tissues of the spinal column, or they can extend directly to the spinal column from contiguous paraspinal lesions. Metastatic tumours migrate from distant sites by both lymphatic or haematogenous routes, and account for 97% of all spinal column tumours.
The most common metastatic lesions are adenocarcinomas from the following sites:
Certain primary tumours, such as chordoma, osteoblastoma, and plasmacytoma, show a preference for the spinal column, but they represent a small proportion of all spinal lesions. Both primary and metastatic malignancies tend to originate in the vertebral body, involving one or both pedicles. Most of the haematogenous marrow is also contained in the bodies. Retrograde flow through the venous drainage of the spinal column (Batson's plexus) permits tumour cells from the abdominal cavity to seed the vertebral bodies directly. Lesions of the posterior elements are more commonly benign.
Pain and neurological dysfunction are the most common presenting symptoms and usually arise from one of the following causes:
- Pathologic fracture
- Expansion of the vertebral cortex and surrounding tissues by tumour
- Compression or invasion of nerve roots
- Segmental instability
- Spinal cord compression
Although radicular symptoms may simulate herniated nucleus pulposus, symptoms from lumbar and sacral neoplasms do not respond to rest and recumbency, and they tend to progress relentlessly. Spinal deformity is rarely associated with spinal neoplasia, except when vertebral collapse results in severe kyphosis. Deformities associated with tumours may come on suddenly and progress rapidly. If the primary lesion is addressed in a timely manner, the curve will often resolve with observation or bracing. However, if the deformity is allowed to persist, surgical correction may be necessary. Neurological injury is rarely the first sign of a spinal neoplasm, but it should be watched for.
A basic workup of any spine tumour must includes the following:
- A full blood cell count, differential, sedimentation rate, urinalysis, Electrolytes, calcium, and basic chemistry panel
- Serum and urine protein electrophoresis; if positive, bone survey and bone marrow aspirate
- Renal ultrasound or abdominal computed tomography (CT)
- Chest CT
- Bone scan
- Physical examination of breasts, prostate, rectal, stool guaiac, thyroid
A. Plain Films
Standard anteroposterior and lateral roentgenograms of the spine. The benign or malignant nature of the lesion can often be implied from the pattern of bone destruction.
B. Nuclear Scans
Bone scans screen for bony turnover can detect the presence of tumours before becoming apparent on plain films. Remember they can be negative in myeloma where there is no hyperaemia surrounding the lesion.
C. Computed Tomography
Computed tomography may provide diagnostic information on small tumour foci early in their development, before extensive bony destruction or intramedullary extension has occurred, and before cortical erosion has advanced to the point of impending fracture. Once the suspected lesion is identified on plain films or bone scan, however, CT provides unsurpassed imaging of the bony architecture.
D. Magnetic Resonance Imaging
MRI provides multiplanar images of large segments of the spine and surrounding tissues and can be used to screen for disseminated disease. It can reveal invasion of paravertebral structures and with gadolinium enhancement it can differentiate osteoporotic compression fractures from metastatic disease.
Previously the gold standard for spinal imaging, this test has been largely replaced by MRI. When MRI cannot be done, myelography with postmyelogram CT may provide the same information.
Needle biopsy allows aspiration and removal of fine tissue fragments. The advantages are that needle biopsy is minimally invasive and uses local anaesthetic. It is most suitable for lesions that are easily differentiated. Because samples are small, they are difficult to read, and they are frequently not diagnostic.
Open biopsy provides moderate-size specimens showing cellular architecture and marginal tissue. It provides diagnostic tissue and may be done just prior to formal excision when used with frozen section. Open, excisional biopsy includes removal of all tumour tissue at the time of biopsy.
Metastatic disease is the most common malignancy of the spine in children with Neuroblastoma accounts for nearly one third of all paediatric spinal tumours. Ewing's sarcoma is the most common primary malignancy, but it often presents as a metastasis than a primary lesion. More importantly 70% of primary paediatric tumours are benign.
The correct treatment of any tumour depends on a number of factors unique to the individual patient:
- Is the tumour benign or malignant?
- Is it primary or metastatic?
- Is the patient systemically ill, or healthy?
- Is the lesion slow growing, locally aggressive, or disseminated?
- Are there any neurological compromise or red flag symptoms?
- Is there a pathological fracture or instability?
Principal indications for surgical treatment include the following:
- Inability to obtain a tissue diagnosis by other methods
- Neurological compression due to pathologic fracture or bony impingement
- Mechanical instability, with severe pain or impending neurological injury
- Tumour progression despite, or following, radiotherapy
- Known radioresistant tumour
- Primary malignant tumour
- Resectable solitary metastasis in patient with potential long-term survival
Three issues must be considered in developing a surgical plan.
- The proper margin of Resection
- Need for neurological decompression
- technique for reconstruction.
The surgical approach and resection margins are planned using Weinstein's staging system, which divides the vertebral body into four zones and three grades of tumour extension.
Tumours in zones 1, 2, and 3 involve the posterior elements, pedicle and transverse process, and anterior vertebral body, respectively. Zone 4 lesions involve the posterior portion of the vertebral body and that portion of the cortex just anterior to the spinal cord or neural elements. To address any lesion involving zone 4, the surgeon must cross zone 3 and must release the vertebra from the pedicles, resecting zones 1 and 2 as well. Zone 4 lesions frequently require a subtotal or total vertebrectomy to obtain a clean margin. This assumes that the tumour is still intraosseous (grade A), without extraosseous spread (grade B), or distant metastases (grade C). Complete resection of the vertebral body requires separating the posterior structures (zones 1 and 2) from the anterior structures (zones 3 and 4), at the junction between the pedicles and the vertebral body.
The decision to perform anterior or posterior procedures depends on numerous factors.
Generally, lesions involving the Vertebral Body (VB) and causing anterior or anterolateral compression are best approached via anterior or anterolateral routes in which vertebral corpectomy is performed and a biomechanically sound stabilisation construct is placed. Laterally situated lesions can often be adequately resected via a posterolateral approach. Only a minority of cases in which isolated posterior compression is present are best served by laminectomy.
Very high and very low spinal lesions pose a specific challenge. The best initial intervention is posterior decompression and stabilisation.
Extent of Involvement
Extradural metastases involving one or two contiguous levels is best approached via anterior or anterolateral routes, because these allow for direct decompression and the possibility of a construction of a sound fusion mass. If three or more contiguous levels require attention, however, decompression is best achieved using a posterolateral approach combined with posterior fusion and placement of instrumentation, or a combined AP procedure.
Cortical Bone Integrity
Bone quality dictates approach and instrumentation. If adjacent bone is compromised, anterior fusion after anterolateral decompression may not be possible. In such cases, the surgeon should consider posterolateral decompression and placement of posterior instrumentation as a safer alternative.
Local or systemic debility is often a factor when contemplating surgery in the patient with spinal metastases. Anterior cervical approaches through a radiation-exposed neck can be filled with difficulty and complication. The principal reasons for operating on benign tumours are to treat pain and to prevent local tumour expansion.
Intralesional excisions are adequate in many tumour types (e.g., aneurysmal bone cyst, osteoblastoma) and should be carried out through the most direct approach with the least disruption of normal vertebral elements. Locally aggressive (aggressive benign and low-grade malignant) tumours should be treated rigorously, ensuring a clear margin wherever possible. Because recurrent tumours are more difficult to eradicate than primary lesions, these locally aggressive lesions may become unresectable if not adequately addressed in the first place. In primary malignancies, the principal goal of surgical treatment is local control of the disease.
The approach is planned to for adequate resection margin with the least disruption of vertebral stability. Patients with an asymptomatic or minimally symptomatic spinal metastasis often do not require surgery.
For anterior column tumours, anterior and posterior approaches are combined to provide the widest possible margin for local control. A transthoracic or retroperitoneal approach is used to reach the tumour from the front. The spine is stabilised posteriorly with a segmental system at the time of posterior release. The anterior weight-bearing column is restored filling the vertebrectomy defect with tricortical or fibular graft, or with a prosthetic cage. Anterior plate fixation is used to augment overall stability.
Candidates who need surgery often include
- Those with known radioresistant tumours
- Solitary metastasis with potential for wide resection
- Unknown tumour type despite systemic workup and needle biopsy
- Bony compression of neural elements, and
- Mechanical instability and bone destruction.
As an alternative in lesions of the thoracic spine, a costotransversectomy or transpedicular technique is used to access the vertebral body and decompress the anterior aspect of the spinal cord.
The quality of both the decompression and the reconstruction can be improved by employing endoscopic control.
The standard approach to vertebrectomy combines a midline posterior incision with a retroperitoneal, a thoracoabdominal, or a transthoracic approach to the anterior vertebral body.
An alternative approach is to extend the posterior dissection around the side of the vertebral body, completing the vertebrectomy through a posterolateral resection.
Complete vertebrectomy requires both anterior and posterior stabilisation. This aggressive surgical approach improves patient survival and neurological function even when cure cannot be obtained.
Decompression v/s Radiotherapy
As many as 20% of all patients with disseminated carcinoma develop symptomatic spinal cord compression. Compression may result when an enlarging soft-tissue mass encroaches on cord or nerve roots, or when a pathologic fracture results in retropulsion of bone fragments into the canal, vertebral collapse, or kyphosis. Soft-tissue metastasis to the meninges or epidural space may directly compress neural elements. Acute spinal cord compression typically results from rapid tumour growth or pathologic fracture caused by extensive bony destruction. Early treatment is crucial.
Radiotherapy remains the most appropriate treatment for most patients with radiosensitive tumours. Prostatic and lymphoreticular neoplasms are typically radiosensitive, while gastrointestinal and renal neoplasms are often not and thus neurological compromise resulting from these lesions is best treated by operative methods.
Spinal instrumentation and fusion are often needed after tumour resection
- to restore stability,
- prevent progressive deformity, and
- facilitate graft incorporation and fusion.
Surgical Reconstruction and Instrumentation
The principles of surgical reconstruction are:
- Restore/augment the anterior weight-bearing column to prevent vertebral collapse and kyphosis.
- Use posterior instrumentation to provide a tension-band effect after laminectomy, to compensate for lost muscular attachments, and to prevent progressive kyphosis.
- Combine anterior and posterior constructs to restore axial, sagittal, and torsional stability after vertebrectomy.
- Anticipate disease progression