The Investigation

“Seek, and ye shall find…”

–Matthew 7:7

When you are seeing patients with low back pain (and other spinal pain) day in and day out, you quickly realize how easy it is to miss or err in diagnosis (Tables 13-1 and 13-2). As a clinician, you start to “build a better mousetrap” so you do not make these errors. Various investigations will aid in the evaluation and ultimate diagnosis.

Blood Work

The following laboratory tests are useful as a screening mechanism:

Hemoglobin, hematocrit, white blood cell count, differential, microscopic, erythrocyte sedimentation rate, and sometimes C-reactive protein.
Serum chemistries, especially calcium, acid and alkaline phosphatase, and serum protein electrophoresis.
HLA-B27 antigen.

It is a good routine to agree to do the hematologic tests and serum chemistries in the following individuals: patients who have a significant nonmechanical component to their pain, patients with systemic symptoms such as fevers, any patient with an atypical pain pattern or distribution, and all patients who do not respond to standard conservative treatment directed at the mechanical causes of low back pain. Be particularly vigilant in older patients (older than age 55 years).

Bone Scanning (Scintigraphy)

Since the first edition of this book in 1977, bone scanning has come a long way. From whole body scanning for metastases with strontium, a tracer element that is difficult to work with and results in a high radiation dose to the patient, we are now to a stage of selective regional imaging using the workhorse radionuclide of nuclear medicine, technetium-99m-labeled phosphorus (^99mTc).

Indications for Bone Scan

The location of metastatic bone lesions remains the most common indication for bone scanning, and this technology has virtually displaced the radiographic skeletal survey in the adult (except for
multiple myeloma). The second most common reason for considering the use of bone scintigraphy is for early detection of bone infection, days before regular radiographic changes occur. Bone scanning is also being used in detection of osteonecrosis, the study of failed joint prostheses, the investigation of unexplained bone pain (especially in the high-powered athlete who may suffer a stress fracture), and the dating of fracture age (1, 2).

Technetium-99M-Labeled Phosphorus

^99mTc is currently the most frequently used radionuclide in nuclear medicine (5). This predominance exists because the radionuclide is readily available and cheap and has an ideal biologic behavior
pattern. This includes easy incorporation in bone, timing of incorporation that suits hospital procedures, and a low radiation dose to the patient.

TABLE 13-1 Differential Diagnosis of Nonmechanical Low Back Pain

Causes of nonmechanical low back pain

Referred pain (e.g., from the abdomen or retroperitoneal space)

Infection

Bone

Disc

Epidural space

Neoplasm

Primary (multiple myeloma, osteoid osteoma, and so on)

Secondary

Inflammation: arthritides such as ankylosing spondylitis

Miscellaneous metabolic and vascular disorders such as osteopenia and Paget’s disease

TABLE 13-2 Differential Diagnosis of Sciatica

Intraspinal causes

Proximal to disc: conus and cauda equina lesions (e.g., neurofibroma, ependymoma)

Disc level

Herniated nucleus pulposus

Stenosis (canal or recess)

Infection: osteomyelitis or discitis (with nerve root pressure)

Inflammation arachnoiditis

Neoplasm: benign or malignant with nerve root pressure

Extraspinal causes

Pelvis

Cardiovascular conditions (e.g., peripheral vascular disease)

Gynecologic conditions causing sacral plexus pressure

Orthopaedic conditions (e.g., osteoarthritis of hip)

Sacroiliac joint disease

Neoplasms (invading or compressing lumbosacral plexus)

Peripheral nerve lesions

Neuropathy (diabetic, tumor, alcohol)

Local sciatic nerve conditions (trauma, tumor)

Inflammation (herpes zoster)

FIGURE 13-1. Bone scan (Tc-99m) showing a hot spot in L2—a metastatic tumor.

This is the basis of the “hot spot” (Fig. 13-1).

Gallium Scanning

^99mTc-labeled phosphorus scanning identifies areas of increased bone turnover and is nonspecific for infection. This led to the search for compounds that would specifically bind to sites of infection, the most popular (until recently) being gallium 67 citrate (⁶⁷Ga). This tracer binds to transferrin and other proteins associated with inflammation and infection. Unfortunately, it emits four gamma rays (photons) ranging from low to high energy, which cause more patient exposure to radiation while making the scan less clear.

More recently, a number of reports on the limited accuracy of gallium scanning, especially in low-grade infections, are appearing in the literature (3, 4).

Indium-111-Labeled Leukocytes

Because of the limited accuracy of ⁶⁷Ga scanning, further research has led to the proposal that indium-111-labeled leukocytes have a greater specificity for musculoskeletal (and other) infective foci.

Single Photon Emission Computed Tomography (Spect)

Normal nuclear imaging is recorded on only two planes [anteroposterior (AP) and posteroanterior and/or lateral] of the three-dimensional skeleton. The significant overlapping of anatomic structures can blur the localization of radionucleotides in the posterior elements of the lumbar spine. With more sophisticated camera systems and the principle of rotating the gamma camera 360
degrees, multiplanar images of the spine, similar to computed tomography (CT), can be obtained. The rotation of the more sensitive cameras minimizes the superimposed activity from over- or underlying structures that occurs in planar imaging. The principles of “slicing” tissue planes into thin wafers that is discussed later in the CT sections applies to SPECT scanning.

Conclusion

Although bone scintigraphy is commonly used today, major changes in nuclear imaging are occurring and will change the indications for use of bone scintigraphy. An example is SPECT, a newer imaging technique just discussed.

Plain Radiographs

In the assessment of routine mechanical low back pain, the question always arises, “Should a radiograph be taken?” A radiograph is not harmful, but it is about as illogical to take a radiograph of every patient who has a backache as it is to order a barium study on every patient who has a touch of indigestion. A radiograph on the first attendance of a patient with back pain is, however, indicated under the following circumstances:

Severe back pain after significant trauma.
Incapacitating back pain.
A history suggestive of vertebral crush due to osteoporosis or malignancy. These patients, usually older than 50 years, report a history of pain coming on without provocative injury, punctuated by sudden cramps of pain in the back.
The excessively anxious patient. In such people, a radiograph is an essential part of treatment. These patients cannot be reassured by clinical examination alone.
Patients in whom the history and examination are suggestive of ankylosing spondylitis. A specific request should be made for views of the sacroiliac joint.
Patients with a clinically apparent spinal deformity.
Patients with significant root tension and those presenting evidence of impairment of root conduction. In these patients, a radiograph is of importance to exclude the possibility of malignancy.
If severe pain persists despite treatment for more than 2 weeks, a radiograph is indicated, not only to exclude the possibility of some obscure spinal abnormality but also to reassure the patient that he/she is not suffering from a serious progressive disease.

Radiographs have limited function in diagnosis and treatment. In diagnosis, the main function of a radiograph is to exclude serious disease, such as infections, ankylosing spondylitis, and neoplasms. If radiographs of the spine show disc degeneration, this radiologic change merely demonstrates a segment that is vulnerable to trauma. Such a demonstration, however, does not necessarily indict this segment as the cause of the presenting symptoms. Treatment is determined by clinical assessment not by the radiologic findings.

The term “degeneration” implies to the average patient a type of “rotting away,” like bad cheese. A patient should never be presented with the bald statement, “the radiographs of your spine show arthritis.” First, this is rarely true. The presence of osteophytes or, more correctly, “spondylophytes” on the vertebral bodies does not denote arthritis. Second, the term “arthritis” carries with it an evil connotation for the patient. Given this diagnosis, the patients frequently foresee a progressive restriction in their way of life leading eventually to a wheelchair existence.

Detailed assessment of radiologic findings indicative of mechanical insufficiency of the spine is only of value in the preoperative assessment of a patient. At this time, a thorough analysis of the radiographic findings is of importance in determining whether surgical intervention is feasible and, if so, the type of operative correction required.

In reading plain radiographs (Fig. 13-2), look at the nonskeletal areas first. Review the retroperitoneal area with specific regard to the kidneys and ureters and the abdominal aorta. Be sure that the psoas shadows are intact. After reviewing the nonskeletal part of a lumbar spine radiograph, consider the skeleton. Look at the sacroiliac joints, survey the pedicles and vertebral bodies for erosions, and finally consider the structural defects that may have a potential for causing the patient’s syndrome. Such observations as narrowing of the disc space and translation of vertebral bodies should
be noted, and may turn out to be important. Various measurements on plain radiographs are not helpful in assessment of canal or recess narrowing.

FIGURE 13-2. A: Standard AP with psoas shadows evident, no abnormal kidney shadows, no calcification in aorta, and normal joints. Note the congenital lumbosacral anomaly. B: Lateral showing good disc space integrity and no vertebral body translations (“slips”).

Myelography, Computerized Axial Tomography, and Magnetic Resonance Imaging

The demands of lumbar spine surgery require a precise definition of not only the nature of the lesion but also the location of the offending pathology. This can be provided only by CT scanning or magnetic resonance imaging (MRI). It is getting more difficult to meet the requirements of precise surgical technique with myelography alone, which results in an increased use of CT scanning and MRI. At the time of this writing, MRI is assuming a primary role in patient assessment because it has the potential to deliver all of the necessary information on which to base a surgical game plan. In this milieu of change in imaging technique, myelography is assuming a less important place in investigation.

Philosophy of Investigating a Patient with Lumbar Disc Disease

The cornerstone of diagnosis of lumbar disc disease is the history and physical examination—not the investigation.

CT and MRI are ordered for two reasons: (a) almost always to verify the clinical diagnosis as correct and at the same time to plan a surgical approach to the problem and (b) infrequently to solve a differential diagnosis problem.

Investigative procedures used to resolve a differential diagnostic problem may fall short of helping to plan surgery. An example is the water-soluble myelogram, which was the “gold standard” for diagnosis of lumbar disc disease. It is valuable in differential diagnosis, such as ruling out a conus tumor, but it fails to provide all of the necessary information to plan a surgical procedure, especially one with limited exposure.

When viewing the investigation, do so in light of the clinical information. You are seeking to identify the anatomic level and the structural lesion. If there is not a perfect marriage among the clinical presentation, anatomic level, and the investigation, something is wrong. To proceed with surgery at this stage sets the stage for a poor outcome.

Consider the following clinical information and respective implications:

A patient with an acute radicular syndrome with significant straight leg raising (SLR) reduction and S1 neurologic symptoms and signs should have an unequivocal lesion involving the S1 nerve root on CT scan or MRI.
A patient with anterior thigh pain and a positive femoral stretch with a decreased knee reflex should not be accepted as having a herniated nucleus pulposus (HNP) at L4-L5 unless it extends into the foramen to involve the fourth root.
A patient with a long history of back pain and claudicant leg pain should have a clear-cut stenotic lesion on investigation before making the diagnosis of spinal stenosis.

The potential for false-negative and false-positive investigative findings is great (17). CT scans and MRIs are so sensitive that it is possible to show pathology in almost every patient. CT scans show only what is scanned. If a conus tumor is present, and the scan is confined to L3 to the sacrum, the lesion will be missed. MRI covers this CT deficiency but at the same time introduces many false-positive results because of overinterpretation. Beware of the clinical diagnosis lacking substance and borderline investigative findings.

A poor quality investigative test is no good to anyone. An extradural myelogram cannot be interpreted, a poorly done electromyograph is misleading, a blurred CT scan is useless, and a patient rushed through an MRI machine will result in a bad MRI scan. It is essential for clinicians to keep the pressure on our radiologic colleagues to deliver the best quality images possible to reduce the risk of operative misadventure.

There is a tendency in the United States to order major spine investigative procedures too early in the progress of disc disease. Tests such as myelography, CT scanning, and MRI are part of an operative procedure; they are not routine radiographs to be ordered without hesitation. If a clinician is in trouble with spine differential diagnosis to the point where frequent myelograms or myelogram/CT scans and MRI are part of the practice routine, then a careful clinical examination is missing. If a significant number of tests ordered by a clinician are negative, the indications for ordering such radiologic tests are too broad and need to be reassessed. Almost every myelogram, CT scan, or MRI examination of the lumbar spine should be positive and followed by an operation. If this is not the case, indiscriminate early ordering of these tests is occurring.

History

“Myelography” was introduced in 1922 by Sicard (15)., using iodized poppy seed oil (Lipiodol) injected into the epidural space. Steinhausen et al. (16). at the University of Rochester introduced iophendylate in 1940, and Pantopaque remained the medium of choice for years. The difficulty in using large needles necessary to introduce the viscous fluid, the necessity of poststudy removal of the contrast material sometimes injuring nerve roots, late arachnoiditis, and other complications (7). led to the incongruous situation of many surgeons ordering the test, yet few themselves prepared to submit to the procedure. Obviously, Pantopaque was not a great medium for myelography, which stimulated the search for better agents. By the mid-1970s, water-soluble contrast agents had virtually eliminated Pantopaque for lumbar myelography, and since the late 1980s we have had available relatively nontoxic, cheap, water-soluble agents; these newer myelographic agents have been developed all in time to see myelography being surpassed as the procedure of choice by better CT scanning and newer MRI (7, 9, 11).

Dynamic Examination

Some radiologists use flexion/extension films to accentuate midline stenotic lesions. Patients with spinal stenosis aggravate their symptoms in extension and are likely to show more of a myelographic defect in this position.

Adverse Reactions to Myelography

Severe adverse reactions to the instillation of contrast material occur in approximately 1:35,000 procedures. They can be divided into adverse neurologic reactions (13)., anaphylactoid reactions, and renal toxicity.

Anaphylactoid reactions are rare, especially with the newer water-soluble contrast materials. Screening of patients historically, corticosteroid and antihistamine pretreatment when indicated, and in some cases refusing to do myelography in a sensitive patient have reduced the incidence of anaphylactoid reactions to a minimum.

Renal toxicity from the doses of contrast material used for lumbar myelography are much rarer compared with the use of the higher doses of these agents that are used for vascular studies. There is a possibility that a patient with pre-existing renal disease can have a toxic reaction from intrathecal water-soluble contrast agents (8).

Adverse neurologic reactions (7,9,11,14) are the reactions that concern myelographers. They include, most frequently, headache, nausea, and vomiting; less frequently, the following reactions occur: increased pain, seizures, myoclonic spasms, psychomotor disturbances, fever, vertigo, and urinary retention.

Patients prone to adverse effects are the older patient, the patient with a previous reaction, and the long-term psychoactive drug user; extra precautions are needed with these patients. Most important, it is necessary to identify these patients with a careful preinjection history.

Myelogram Changes

Figure 13-3 demonstrates a normal myelogram. Abnormalities in myelography indicative of an HNP are as follows:

Defects in the sac alone. The most difficult defects to interpret involve the dural sac alone. A double density (Fig. 13-4) is usually indicative of a disc herniation toward the midline, but
still eccentric enough to produce the typical defect. On occasion, an HNP fragment will migrate up or down from a disc space and produce a defect on the sac alone (Fig. 13-5). Simple, smooth midline defects are not to be interpreted as HNP (Fig. 13-6). These defects are known as “sucker discs” and are caused by annular bulging as part of the phenomenon of degenerative disc disease. Often, they will be accompanied by degenerative changes, especially retrospondylolisthesis.
Defects affecting the root sleeve. The low viscosity of water-soluble contrast materials makes it possible to readily fill the root sleeves (radiculogram). The defects demonstrated can be an absent root sleeve (Fig. 13-7).
A root sleeve shortening or cut-off (Fig. 13-8), a root sleeve deformity (Fig. 13-9), and a swollen root sleeve (Fig. 13-10).
Defects affecting sac and root. These are the most obvious defects and are depicted in Figure 13-11.

FIGURE 13-3. A normal AP myelogram.

FIGURE 13-4. A lateral myelogram with a double density at L5-S1 and annular bulging deforming the sac at L4-5.

Sensitivity and Specificity of Myelography

Although there are numerous reports in the literature on false-positive and false-negative myelograms (9, 10)., most reports are poor in that they do not follow up on patients to completion of treatment. False-negative myelograms can still occur with water-soluble agents in the following situations:

Foraminal HNP (Fig. 13-12).
Unscanned area (high lumbar disc not scanned).
Insensitive space at L5-S1 (Fig. 13-13).
Short or narrow dural sac at L5-S1 (Fig. 13-14).
Conjoint nerve roots distorting the contrast column.

Outpatient Myelography

With the North American desire to ration health care (contain costs), more patients are undergoing outpatient myelography (6). In the second edition of this book we did not support outpatient

myelography. With the increasing use of low-osmolality contrast agents, outpatient myelography is most often completed without adverse patient events.

FIGURE 13-5. AP myelogram showing a large herniated nucleus pulposus (HNP) behind the vertebral body of L5 distorting the sac (the S1 root is also obliterated) (arrow).

FIGURE 13-6. Lateral myelogram showing annular bulging at L4-L5. This is the lateral of Fig. 13-3, the so-called sucker disc.

FIGURE 13-7. AP myelogram showing S1 root sleeve absent on right (herniated nucleus pulposus, L5-S1, right) (arrow).

FIGURE 13-8. Root sleeve shortening on AP myelogram (arrow). Compare the length of S1 root filling on the right (shorter) with the left S1 root. Now, compare the shortening of this S1 root with the absence of the S1 root in Fig. 13-7.

FIGURE 13-9. AP and oblique myelogram showing herniated nucleus pulposus (HNP) L4-L5 distorting the LS root sleeve (arrow).

FIGURE 13-10. The S1 root, left, is swollen (arrow). (Compare with the L5 root at the level above.)

FIGURE 13-11. A: AP myelogram showing herniated nucleus pulposus (HNP) L4-L5, left, with significant distortion of sac and root. This is a large HNP that has trapped down behind the vertebral body of L5. B: Apparent defect of sac and root, L4-L5, right. Did you notice the absent pedicle, L5, right (arrow)? This was a secondary carcinoma from a lung malignancy.

Conclusion

Virtually no one is doing myelography alone these days; almost all myelograms are followed by a CT examination. The issue today is whether to continue to use CT myelography or switch to MRI as the primary investigative step before surgery. We prefer the MRI, but there are still situations where a myelogram, followed by CT, is indicated:

An equivocal CT or MRI in a patient who the surgeon feels has a surgical lesion.
An obese patient who cannot fit into the CT or MR gantries.
Multilevel spinal stenosis, especially with scoliosis (scoliosis interferes with proper CT or MRI “slicing” of each segment).
Patients in whom metal implants (e.g., pedicle screws) will distort the CT scan or MRI.
Less-than-optimal MRI scanning machines (which are not that uncommon).

High-Resolution Computed Tomography

It is becoming more difficult to plan a surgical procedure on the spine without investigation that shows not only the level but also the precise location and nature of the pathology. Myelography is often capable of showing the level at which the pathology lies (20). but fails to show the nature of the lesion or its precise location in the anatomic segment (18, 25). (see Chapter 1). This limits the value of water-soluble myelography in surgery for lumbar disc disease, a void that is fortunately filled by CT scanning and, more recently, MRI.

FIGURE 13-12. Foraminal herniated nucleus pulposus (HNP), L4-L5, right. Arrow points to slight distortion of contrast column, a change easily missed.

FIGURE 13-13. Lateral myelogram showing wide “insensitive space” between back of L5-S1 disc space and front of “dye” column where pathology, such as a herniated nucleus pulposus (HNP), could reside and not be detected on myelography.

FIGURE 13-14. AP myelogram showing a short dural sac, ending before it reaches the level of L5-S1. There is no hope that this myelogram would reveal a herniated nucleus pulposus (HNP) of L5-S1. Fortunately, the HNP was at L4-L5, left, demonstrated by an absent root.

Advantages and Disadvantages

Table 13-3 lists the advantages and disadvantages of CT scanning. The most serious problem with routine CT scanning is the ease with which the procedure can be done. With no requirement for hospitalization or injection into the body, the CT scan becomes too simple a step to take, and this procedure is capable of delivering erroneous data (30). that can lead to ill-advised surgical intervention.

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