Pyogenic Spondylodiskitis

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Abstract
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.