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Technical Innovation |
1 All authors: Department of Radiology, Orthopedic University Hospital Balgrist, Forchstrasse 340, Zurich, Switzerland 8008.
Received January 21, 2005;
accepted after revision June 14, 2005.
Address correspondence to C. W. A. Pfirrmann.
Abstract
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CONCLUSION. CT-guided core biopsy of subchondral bone and intervertebral space compares favorably to previously published studies because histology can provide the diagnosis even when no specific infectious agent is isolated.
Keywords: biopsy • infectious diseases • interventional radiology • musculoskeletal imaging • spine • spondylitis
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MRI is more sensitive and specific in the diagnosis of spondylodiskitis than standard radiography but also has limitations [8]. On MR images, signal alterations may be difficult to differentiate from other abnormalities such as fibrovascular tissue in degenerative disk disease (Modic 1 abnormalities) [9, 10] or dialysis-related intervertebral disk disease [11]. Scintigraphic techniques encounter similar problems [12, 13]. Therefore, biopsy is commonly performed before treatment.
The accuracy for percutaneous disk-space biopsy has been reported to be as low as 47.5-57% in the diagnosis of spondylodiskitis [14, 15]. According to our own experience and that of the spine surgeons at our institution, paravertebral abscesses or fluids obtained from the disk space are often sterile. Because hematogenous spondylodiskitis typically originates at the subchondral part of the vertebral body before involving the intervertebral disk [16], subchondral bone has routinely been included in the biopsy specimen obtained at our institution.
The purpose of this study was to determine the diagnostic performance of CT-guided core biopsy including both intervertebral disk and subchondral bone in suspected spondylodiskitis and to compare the results to those previously reported for other biopsy techniques.
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The patient was positioned in the prone position. Under aseptic conditions (triple disinfection, sterile cover, gloves, and surgical mask), local anesthesia was performed with a 7-cm, 20-gauge needle. Ten milliliters of mepivacaine (Scandicain 2%, Astra-Zeneca) was typically applied to the skin, the planned needle track, and predominantly to the bone surface. A small skin incision was then made. Biopsy was performed with a 3 or 4 mm (11 or 8 gauge) in diameter trap system bone biopsy needle (Hospital Services S.p.A.). Twenty-eight of the 41 biopsies were performed through the transpedicular route and 13 through a posterolateral approach (with the needle entering the posterolateral vertebral body close to the intervertebral space) (Fig. 1). Care was taken that both disk material and subchondral bone were included in the specimen. For this purpose, the biopsy track was commonly chosen perpendicular to the tabletop, which is often slightly oblique in relation to the endplates and intervertebral disks, making it possible to obtain material from both structures with a single biopsy (Fig. 2).
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If the endplates were parallel to the perpendicular needle track or angulated superiorly (which most commonly occurs in the upper lumbar and the lower thoracic spine), the needle was cranially angulated to reach both the endplate and the intervertebral space with a single biopsy. The entry site and needle placement were controlled by CT fluoroscopy to ensure proper needle placement in case of a moving patient. The biopsy was performed at L3-L4 (n = 4), L4-L5 (n = 9), L5-S1 (n = 9), T11-T12 (n = 5), L2-L3 (n = 4), T8-T9 (n = 3), T10-T11 (n = 2), and once each in T2-T3, T3-T4, T7-T8, T9-T10, and L1-L2. The biopsy was performed either at the upper or lower endplate. The endplate with more MRI changes and better anatomic accessibility was chosen.
In all 41 patients, a biopsy sample was sent for microbiologic examination. In 35 of the 41 patients, the biopsy sample was divided into two parts for microbiologic and histologic evaluation. The histology specimens were fixed in formalin (4%) and stained with H and E. In 11 specimens, Gram and Ziehl-Neelsen stains were added.
In seven patients, open surgery was performed for surgical débridement with or without fusion. In all of these seven patients, additional microbiologic and histologic examinations were performed. The final diagnosis of spondylodiskitis (standard of reference) was made when an infectious agent was isolated in the percutaneous or surgical biopsies or when histology showed acute osteomyelitis or diskitis in combination with a clinical follow-up compatible with the diagnosis. Spondylodiskitis was excluded in the presence of negative bacteriology and negative histology and when imaging (bone marrow signal alterations next to the intervertebral disk at MRI) and clinical (pain and limited range of motion) findings decreased during follow-up without antibiotic therapy. All three criteria had to be available for a negative diagnosis. All radiology reports and patient charts were reviewed for complications related to the biopsy.
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Microbiology
Microbiologic examinations were available in all 41 patients. Of the 18
patients with spondylodiskitis, 11 had positive bacteriologic examinations and
7 had negative examinations. Staphylococcus aureus was most commonly
found (n = 5). Two patients had a Streptococcus infection
(type not further specified), and one each an Escherichia coli,
Mycobacterium tuberculosis, Citrobacter koseri, and Propionibacterium
acnes. With 11 true-positive, 7 false-negative, 23 true-negative, and no
false-positive results, microbiology obtained after percutaneous biopsy had a
sensitivity of 61%, a specificity of 100%, and an accuracy of 83% in the
diagnosis of spondylodiskitis. In two of the seven patients who had
spondylodiskitis but had a negative percutaneous microbiologic examination,
surgical biopsy later revealed P. acnes and M. tuberculosis
infections, respectively.
Histology
Sixteen of the 18 patients with spondylodiskitis had histologic
examinations. Of these 16 patients, 13 examinations were true-positives and
three were false-negatives. Nineteen of the 23 patients without
spondylodiskitis had histologic examinations, all of which were
true-negatives. This results in a sensitivity of 81%, a specificity of 100%,
and an accuracy of 91% for histology. Histology was positive for
spondylodiskitis in five patients with negative microbiologic examinations.
Conversely, histology was negative in three patients with positive
microbiology.
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Because of the difficulties of noninvasive imaging techniques in diagnosing or excluding spondylodiskitis, biopsy is commonly performed before treatment. Fine-needle aspiration [20-29], percutaneous core biopsy [30-33], laparoscopic biopsy [34], and surgical biopsy [35] have been investigated. For all techniques, identification of the infectious agent is challenging. Our results are comparable to other investigations including the 57% positive spine biopsies found by Rieneck et al. [27]. Possible explanations for negative results at microbiologic examination include antibiotic treatment initiated before the biopsy, insufficient number of infectious agents in the biopsy material, and biopsy obtained from a location without living infectious agents. However, not even microbiologic tests performed in surgical biopsies can perform any better, at least not after antibiotic therapy [4, 22].
In our series we had a relatively high number of false-negative results (7/18) with microbiology; however, histology was positive for spondylodiskitis in five patients with negative microbiologic examinations. We therefore believe that the combination of both examinations is the optimum. This is in line with White et al. [36] proposing that histologic examinations should routinely be performed in suspected spondylodiskitis.
Although characteristic histologic findings are present in infection, such as increased numbers of polymorphonuclear leukocytes, there is a partial overlap in the histologic appearance of degenerative type 1 endplate abnormalities and intervertebral space infection similar to the findings with MRI [37]. In the study of Chew and Kline [22], the diagnostic performance of microbiologic examinations was superior to our microbiologic results and comparable to our histologic results. The sensitivity was 91% and the specificity was 100%. There may be differences with regard to antibiotic therapy before diagnosis, general health of the study population, referral pattern, and extent of disease. Chew and Kline specifically excluded patients who had endplate abnormalities but no disk disease, which may exclude early disease.
For percutaneous biopsy, mainly fluoroscopy and CT have been used as guiding methods [9, 22, 28, 32, 33]. Fluoroscopy is more readily available than CT, requires a smaller amount of radiation, and allows acquisition of real-time images. CT more precisely shows the needle position and is therefore potentially safer with regard to injury to neighboring structures such as nerve roots. With CT fluoroscopy, near real-time imaging has also become possible. Radiation dose with this method is relatively small in comparison with diagnostic CT, as has been shown in shoulder imaging (0.22 vs 0.96 mSv) [38].
In conclusion, CT-guided core biopsy of intervertebral disks and adjacent endplates compares favorably to most other studies evaluating percutaneous biopsy in suspected spondylodiskitis because histology can provide the diagnosis even when no specific infectious agent is isolated.
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