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Current Surgical Management of Metastatic Spinal Disease

Current Surgical Management of Metastatic Spinal Disease

ABSTRACT: Despite advances in the treatment of many malignancies, a large number of cancer patients will require evaluation and possible surgical intervention for lesions that have metastasized or directly invaded the spinal column. The need for heightened awareness of and aggressive early intervention for spinal metastases is underscored by many studies that have reported a relationship between pretreatment and posttreatment neurologic function in these patients. Recommendations for operative intervention should be made following an evaluation of the patient by multiple specialties, both medical and surgical. In the last decade, advances in surgical techniques for tumor decompression and spine stabilization, neurophysiologic monitoring, and anesthetic expertise have allowed surgeons to perform more extensive procedures with improved outcomes and reduced morbidity. This article will review the factors favoring an operative recommendation in patients with metastatic spinal disease, preoperative evaluation, and available surgical options. Patients with symptomatic spinal metastases should receive early surgical consultation as part of a multidisciplinary approach to their disease process. [ONCOLOGY 14(7):1013-1024, 2000]


Introduction

The spinal column is the
most frequent site of bony metastasis.[1,2] Metastatic spinal disease
is a significant problem for a large number of cancer patients.
Between 5% and 10% of all cancer patients develop spinal metastases
during the course of their disease.[3] Approximately 40% of persons
dying of cancer will have autopsy evidence of spinal metastases,[3-5]
and 10% of these will develop spinal cord compression with subsequent
neurologic deficits.[6,7] The annual incidence of spinal cord
compression secondary to spinal metastases is estimated to be 20,000.[8]

A recent autopsy study found metastatic involvement of the spine in
90% of patients with prostate carcinoma, 75% with breast carcinoma,
55% with melanoma, 45% with lung carcinoma, and 30% with renal
carcinoma.[9-11] Clinically significant (symptomatic) spinal cord
compression is observed in a higher percentage of patients with
certain carcinomas—22% of patients with breast cancer, 15% with
lung cancer, and 10% with prostate carcinomas.[10]

In almost 10% of cases of newly diagnosed spinal metastases, the
patient is not known to have cancer, and spinal cord compression is
the initial symptom of the malignancy.[12] Half of these patients are
subsequently found to have lung cancer. The time between the original
diagnosis of cancer and the occurrence of spinal metastases varies widely.

There is a slight preponderance of metastatic spinal tumors in males
(60%) compared to females.[13] This gender difference may reflect the
incidence of primary breast vs prostate tumors and the proclivity of
prostate cancer to metastasize to bone in published series. Spinal
metastases may occur in all age groups, but the period of highest
prevalence coincides with the relatively high cancer risk period of
40 to 65 years of age.[14]

Metastatic spinal lesions involve the vertebral column (85% of
cases), paravertebral spaces (10% to 15%), or the epidural space (£
5%).[15,16] The vertebral body is usually the portion of the
vertebrae that is involved. Spinal metastases can also be noted
intradurally and within the spinal cord itself (intramedullary).[16,17]

Metastatic spread to bone may be related to osteotropism of the
malignant cells, direct spread, and/or the highly vascular supply of
bone marrow.[2] Batson and others have demonstrated that the
vertebral venous plexus draining the thoracic, abdominal, and pelvic
viscera (Batson’s plexus) is a route of metastases to the spine.[18]

Most metastatic spinal lesions (70%) are found at the thoracic level,
20% in the lumbar region, and 10% in the cervical region.[15] The
increased frequency of spinal metastases in the thoracic vertebrae
may be related to the greater number of thoracic vertebrae, compared
to vertebrae in the lumbar and cervical regions. Metastatic lesions
occur at multiple noncontiguous levels in 10% to 38% of cases.[15,19,20]

The incidence of metastatic spinal disease is likely to increase in
the future, due to several factors. Improvement in diagnostic
capabilities, especially the widespread availability and sensitivity
of magnetic resonance imaging (MRI), may increase the number of
metastatic lesions detected and patients evaluated. Progress in the
treatment of many cancers using multimodality regimens will
undoubtedly lead to a prolongation of patient survival, with the
resultant development of more spinal metastases. Finally, earlier
detection of malignant primary lesions as part of screening programs
and improved diagnostic tests will result in progressive increases in
the number of spinal metastases detected.

Patient Evaluation

History and Physical Examination

Pain is the most common presenting symptom of patients with
metastatic spinal tumors.[15,21,22] The etiology of pain may be tumor
spread, spinal instability, nerve root or dural irritation, or direct
cauda equina or spinal cord compression. Pain may also be related to
bony destruction or invasion of paraspinous tissues, such as muscles
or ligaments.[23]

Patients with spinal metastases frequently describe the pain as a
dull, constant ache and often complain that the pain awakens them
from sleep.[22] Occasionally, the pain will occur in a radicular
distribution, which may be caused by nerve root irritation.

Muscular weakness is frequently manifested by the progressive
inability to ambulate or the loss of limb function. The patient’s
ability to walk at the time of presentation is a sensitive predictor
of the ability to walk after surgery.[24]

Difficulty with ambulation is often slowly progressive, and the
patient compensates for the difficulty by using a cane or other
assistive device, as well as reducing activities. Alternatively, an
ambulatory difficulty may occur rapidly and present as a neurologic
emergency. Occasionally, patients will relate difficulty in walking
to generalized weakness. Prognostically, the ability to walk, absence
of myelopathy, and £ 75% myelographic
block are all associated with preservation of the ability of a
patient to ambulate after treatment.[19]

Sensory dysfunction, while frequently noted on physical examination,
is a rare presenting complaint, although paresthesias are often noted
by patients who are questioned carefully. Similarly, patients tend to
underestimate the loss of bladder and bowel control, or will relate
these difficulties to other medical problems, such as prostatic hypertrophy.

A complete medical history, including a treatment history, must be
obtained. Prior treatment may have included radiotherapy and
chemotherapy. The radiotherapy fields and dosage must be well
defined, as these factors may influence any decision to offer the
patient further radiation therapy for either local disease or for
treatment of metastatic spinal lesions.[25] High skin dosages may
also affect decisions regarding surgical approach and timing.

Significant cardiac dysfunction may influence the decision to offer
surgery, the surgical procedure, or the use of preoperative surgical
adjuncts, such as tumor embolization. Pulmonary dysfunction also
increases perioperative morbidity and mortality. The presence of
disease in these major organ systems may represent contraindications
to surgery that would be expected to result in excessive blood loss
or further lung dysfunction (eg, transthoracic procedures).

An understanding of the rate of disease progression, response of the
tumor to prior treatments, and degree of tumor control is essential.
The patient’s desires and the degree of importance that the
patient places on the preservation of ambulatory function, bladder
and bowel control, and other neurologic functions should also be
considered. The patient and family must have realistic expectations
of the risks and potential benefits of the surgery so that they can
make an informed decision.[23]

A detailed physical and neurologic examination is necessary to
determine the patient’s eligibility for surgery and to establish
a neurologic baseline against which responses to therapeutic
interventions can be compared. The spine is examined for tenderness
to palpation and paraspinous muscular spasm. A localized kyphotic
deformity is an important positive finding. Patient resistance to
active and passive movements is recorded. The neurologic examination
includes an evaluation of mental status and long tract and cerebellar
function to help determine whether intracranial lesions are present
as well.	

Diagnostic Imaging

• Plain spinal radiography is relatively sensitive and
specific for metastatic disease. Plain radiographs may be obtained to
provide baseline information and intraoperative comparison[26] and
can define spinal alignment, the presence of a fracture, and gross
areas of bone involvement by tumor.[27] The majority of spinal
metastatic lesions are osteolytic, with only 5% being
osteoblastic[27]; however, 30% to 60% of the bone must be destroyed
for a lytic lesion to be appreciated on plain radiographs.[9,28]

In one series comprising patients with clinical metastatic spinal
compression, 60% of patients had normal plain radiographs.[27,29]
Although radiographs are frequently employed in initial screening, a
negative plain radiograph does not necessarily indicate the absence
of disease.[27]

Flexion and extension studies may be required for lesions of the
cervical and lumbar spine where extensive bony destruction may be
associated with spinal stability. If instability is not felt to be
present, a nonoperative approach may be sufficient. However, movement
on flexion and extension studies may alone determine the need for
surgical spinal stabilization to prevent future neurologic injury.[30-32]

• Magnetic resonance imaging is now the method of choice
to detect the presence and extent of spinal metastasis.[16,21,33-35]
It provides excellent visualization of soft-tissue involvement, bone
marrow replacement, ligamentous involvement, spinal cord edema, and
degree of canal compromise and cord compression.[36] Magnetic
resonance imaging has the further advantage of being able to image
the entire spine; this may be especially helpful because multiple
lesions that are not suspected clinically are found in up to 30% of cases.[37]

Due to the high sensitivity of MRI for the detection of early changes
in bone marrow, several reports have documented MRI detection of
spinal metastases that were not appreciated on plain radiographs,
radioisotope studies, or computed tomographic (CT) scans.[37-41]
However, false-positive MRI studies have been reported in which
signal characteristics suggestive of metastases were subsequently
found to be nonpathologic reactive tissue within vertebrae.[41,42]

• Computed tomography remains an important imaging tool
in the evaluation of patients with spinal metastases.[20] Axial CT
images provide excellent bony detail of the spinal canal and
vertebral bodies and can help determine whether canal compromise is
due to bone or soft tissue.[43,44] The integrity of vertebral
elements that may be required for internal fixation, such as pedicles
and lamina, can also be determined.[45] Computed tomographic scanning
may be reserved for patients who cannot undergo MRI scanning for
reasons such as the presence of cardiac defibrillators.

• Myelography, especially when combined with
postmyelographic CT studies, can provide an excellent analysis of
both the spinal cord and the vertebral column. In addition,
cerebrospinal fluid can be obtained for analysis during the
procedure. A possible risk associated with myelography is the
development of neurologic deficits in cases of high-grade block when
the lumbar puncture is performed below the level of
disease.[19,46-47] This complication may be avoided by gaining access
to the subarachnoid space via a high cervical cisternal puncture.[27]

• Radioisotope studies, most commonly using
technetium-99m pyrophosphate and diphosphonate compounds, are an
efficient means of detecting bone metastases.[26,48] These studies
identify areas of increased bone deposition, such as blastic-type
metastases but are less useful in detecting purely lytic-type lesions
unless sufficient bone repair is taking place.[41]

Radioisotope studies are specific in only 60% to 80% of patients with
metastatic bone disease.[27] Both CT and MRI imaging have been shown
to be more sensitive for the detection of cervical metastases than
bone scintigraphy.[41]

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