Pyogenic spondylodiskitis: A radiologic/pathologic and culture correlation study

Archives of Pathology & Laboratory Medicine, May 2000 by Lucio, Emmanuel, Adesokan, Adekunle, Hadjipavlou, Alexander G, Crow, Wayne N, Adegboyega, Patrick A

* Background.-Intervertebral disk tissue is resistant to hematogenous infection because of its avascularity. However, spondylodiskitis is being diagnosed with increasing frequency because of advancement in magnetic resonance imaging technology. There is a dearth of information regarding the bacteriology, histomorphologic features, and radiopathologic correlation of spondylodiskitis.

Design.-The study population consisted of 20 patients diagnosed as having spondylodiskitis by magnetic resonance imaging with and without gadolinium 67 enhancement and bone scans with technetium Tc 99m or gallium citrate Ga 67. Twenty-seven biopsy and debridement specimens were obtained from these patients. The specimens were cultured for microorganisms and also processed for histopathologic testing. Tissue sections were examined with hematoxylin-eosin and stains for infectious agents (Gomori's methenamine-silver, Gram, and Ziehl-Neelsen stains).

Results.-Where intervertebral disk tissue was present

(23 of 27 cases), the morphologic changes included vascularization (with or without granulation tissue), myxoid degeneration, and necrosis. Chronic osteomyelitis was present in all 27 specimens and was associated with acute osteomyelitis in 7 cases (25%). Twenty-one of 27 cases had positive culture results (mostly pyogenic bacteria), but special stains revealed microorganisms in sections of the disk in only 4 cases (3 cases with gram-positive cocci and 1 with yeast consistent with Blastomyces). Florid acute inflammation was present in all the 4 cases.

Conclusion.-Histopathologic features of acute spondylodiskitis include vascular proliferation, myxoid degeneration, and necrosis of the disk tissue with adjacent chronic osteomyelitis. Acute inflammation is variable and when florid is usually associated with identifiable organisms on histologic examination. At biopsy, tissue should be submitted for culture, since culture has a high sensitivity and specificity for detecting the etiologic organism.

(Arch Pathol tab Med. 2000;124:712-716)

Spondylodiskitis (inflammation of the intervertebral disk tissue and adjacent vertebrae) is being diagnosed with increasing frequency because of the advancement in magnetic resonance imaging (MRI) technology. With regard to etiology, the disease had been divided into 2 major groups-tuberculous and nontuberculous (nonspecific). In the most recent review of cases, the latter predominates, with pyogenic organisms being the most common cause.1 Only a few articles have addressed the microscopic findings in these conditions with no correlation with microbial culture results.2-4 The objective of this study was to describe the histomorphologic changes and correlate with the bacteriologic findings in spondylodiskitis diagnosed by radiologic imaging studies.

MATERIALS AND METHODS

Patients

The study population consisted of 20 patients admitted to University of Texas Medical Branch at Galveston between September 1995 and August 1997 with the clinical diagnosis of hematogenous spondylodiskitis. All the patients presented with intractable back pain (with or without neurologic deficits) requiring narcotic pain management and bed rest. The diagnosis was confirmed with radiologic studies, which included plain x-ray examinations, MRI studies with and without gadolinium 67 enhancement, and bone scans using technetium Tc 99m (^sup 99^Tc)-medronate diagnostic preparation or gallium citrate Ga 67 (^sup 67^Ga). The patients then underwent percutaneous transpedicular diskectomy and debridement for drainage and antibiotic irrigation. The debrided tissues were submitted for histomorphologic studies, cultures, and antimicrobial susceptibility studies. Postoperatively, the patients were prescribed systemic antibiotic therapy.

Histopathologic and Bacteriologic Studies

Twenty-seven surgical specimens were obtained from the 20 patients involved in this study. A portion of each specimen was submitted for aerobic, anaerobic, mycobacterial, and fungal cultures from the operating room in appropriate transport media. The remaining portion was fixed in 10% neutral buffered formalin solution and then processed for histopathologic testing. The soft tissues were processed routinely for paraffin embedding with subsequent hematoxylin-eosin staining of tissue sections. The bone fragments were fixed in 10% formalin for at least an hour and then decalcified overnight in Redecal (Anapath, Lewisville, Tex). They were then processed routinely for preparation of paraffin-embedded and hematoxylin-eosin-stained tissue sections. The tissue sections were then examined (by light microscopy) for the histomorphologic features of diskitis.

In addition, tissue sections were also examined for the presence of microorganisms with Gram stain for nontuberculous (pyogenic) bacteria, Ziehl-Neelsen stain for acid-fast bacilli (Mycobacterium species), and Gomori's methenamine-silver stain for fungi.

RESULTS

Patients

The study population consisted of 15 men and 5 women who ranged in age from 33 to 84 years old (mean, 50.4 years). The patients' demographic data and sites of the lesions are summarized in the Table. In patients with spondylodiskitis, the nonenhanced MRI showed decrease in signal with loss of distinction between the affected intervertebral disks and the adjacent vertebral bodies. With ^si[ 67^Gd, there was enhancement of the involved intervertebral disks and adjacent vertebral bodies (Figure 1). Also, both ^sup 99^Tc and ^sup 67^Ga bone scans showed increased activity at the affected sites, but the changes observed with ^sup 67^Ga scan was more specific for infectious process. The lumbar segments were the most commonly involved area (17 of 20). No sacral vertebrae below Sl were involved. Only 3 of the 20 patients had involvement of multiple segments of the vertebral column.