CT-guided biopsy in suspected spondylodiscitis
Percutaneous tissue biopsy is a key step in the spondylodiscitis diagnosis and management, often utilizing CT-guided biopsy or fluoroscopy-guided disc aspirations.
Although CT-guided biopsies are culture-positive in a minority of cases, the majority of positive cultures are useful to tailor antibiotic treatment. Empirical treatment with clindamycin may cover almost all micro-organisms in positive biopsy specimens, provided patients are not immunocompromised. Outcome appears similar between culture-positive and culture-negative patients 1).
Inflammatory infiltration of the paravertebral space indicated successful pathogen detection by CT-guided biopsy. Specificity was increased by the additional occurrence of epidural infiltration or paravertebral abscesses 2) 3).
A high CRP was a strong predictor of isolation of the causative organism. Repeat CT-guided biopsy was found to have limited value with a low positive yield (14.2%) in a study 4).
MR imaging is mandatory to determine the optimal biopsy position. No clinical or imaging parameter could rule out a positive biopsy result and thus omit an unnecessary procedure. Biopsy should not be avoided if antibiotic treatment has previously been administered 5).
Overall microbiologic yield of repeat CT-guided biopsy for patients with suspected infectious spondylodiscitis was low at 14.3%; however, a higher yield was identified in patients who were younger in age and not exposed to pre-biopsy antibiotics 6)
Epiduritis and the size of paravertebral edema on MRI are associated with detection of a microbial pathogen in suspected septic spondylodiscitis. For patients without these MRI signs, the need for further investigations such as enriched or prolonged cultures, a second CT-guided biopsy, or even surgical biopsy need to be discussed 7).
Other possible ways of detecting the pathogen are to use a percutaneous punch under anesthesia and CT-guided biopsy with fine needle puncture. The latter can be performed during the same session, to lay a drain to reduce stress on the abscess. A disadvantage of CT-guided puncture is that it gives relatively low quantities of tissue, so that pathogens are only successfully detected in about half of the patients.
Intraoperative sampling – Intraoperative removal of tissue samples is the most reliable method of detecting the pathogen, as it gives relatively large quantities of tissue. The pathogen detection rate is then about 75%
Germ isolation by needle biopsy or open biopsy allows proper antibiotic treatment and faster healing 8).