Post-Operative Spinal Infection¶

Definition¶

Post-operative spinal infection occurs following spinal surgery and encompasses superficial wound infections, deep surgical site infections, discitis, and epidural abscess. The reported incidence ranges from 1–12% depending on the procedure, with instrumented fusions carrying the highest risk. Post-operative infections are diagnostically challenging because normal post-surgical changes can mimic infection on MRI.

Risk Factors¶

Instrumented surgery (hardware provides a surface for biofilm formation)
Prolonged operative time
Diabetes mellitus
Obesity
Malnutrition
Immunosuppression
Revision surgery
Posterior approach (higher infection rate than anterior)

Imaging Findings¶

MRI¶

Post-operative imaging interpretation is complicated by normal surgical changes:

Normal post-surgical findings (not infection): - Vertebral body and endplate edema at the surgical level (expected for 6–12 months) - Enhancement along the surgical tract - Small epidural collections (seromas, hematomas) - Disc signal changes at levels of discectomy

Findings suggesting infection: - Progressive or increasing enhancement on serial imaging (rather than decreasing) - Fluid collection with rim enhancement — suggestive of abscess, especially if it enlarges on serial imaging - DWI restricted diffusion within a collection — supports abscess over seroma - Paraspinal soft tissue enhancement and edema extending beyond the expected surgical bed - Hardware loosening — lucency around screws or rods suggesting infection (or mechanical failure) - New or worsening disc enhancement at or adjacent to the surgical level

CT¶

Fluid collections around hardware
Screw loosening (lucency around screws >2 mm)
Soft tissue gas (can be normal early post-op but abnormal after 2 weeks)

Clinical Pearl

Normal post-surgical MRI findings (endplate edema, tract enhancement, small epidural collections) can persist for 6–12 months and mimic infection. The key is serial imaging — infection shows progressive or worsening changes, while normal post-surgical changes improve over time. DWI is particularly helpful: restricted diffusion within a post-operative fluid collection strongly suggests abscess rather than seroma.

Management¶

Superficial infections — Antibiotics, wound care
Deep infections without hardware — IV antibiotics, possible surgical debridement
Deep infections with hardware — Surgical debridement and irrigation with hardware retention (if stable) or removal (if loose), followed by prolonged antibiotics
Biofilm — A major challenge with instrumented infections; hardware provides a surface for bacterial biofilm that is resistant to antibiotics

Key Points¶

Post-operative spinal infections are diagnostically challenging on MRI due to normal surgical changes
Serial imaging showing progressive enhancement or enlarging collections suggests infection
DWI restricted diffusion distinguishes abscess from seroma
Hardware loosening can indicate infection
Biofilm on instrumentation is a major challenge requiring surgical debridement
Risk increases with instrumentation, diabetes, obesity, and immunosuppression

References¶

Hong SH, Choi JY, Lee JW, Kim NR, Choi JA, Kang HS. MR imaging assessment of the spine: infection or an imitation? RadioGraphics. 2009;29(2):599-612. https://pubs.rsna.org/doi/10.1148/rg.292085137
Kim SJ, Lee SH, Chung HW, Lee MH, Shin MJ, Park SW. Magnetic resonance imaging patterns of post-operative spinal infection: relationship between the clinical onset of infection and the infection site. J Korean Neurosurg Soc. 2017;60(4):448-455. https://pmc.ncbi.nlm.nih.gov/articles/PMC5544379/
Dowdell J, Brochin R, Kim J, Overley S, Oren J, Freedman B, Cho S. Postoperative spine infection: diagnosis and management. Global Spine J. 2018;8(4 Suppl):37S-43S. https://pmc.ncbi.nlm.nih.gov/articles/PMC6295816/
Corona-Cedillo R, Saavedra-Navarrete MT, Espinoza-Garcia JJ, Mendoza-Aguilar AN, Ternovoy SK, Roldan-Valadez E. Imaging assessment of the postoperative spine: an updated pictorial review of selected complications. Biomed Res Int. 2021;2021:9940001. https://pmc.ncbi.nlm.nih.gov/articles/PMC8154286/
Parchi PD, Evangelisti G, Andreani L, Girardi F, Lebl D, Sama A, Lisanti M. Postoperative spine infections. Orthop Rev (Pavia). 2015;7(3):5900. https://pmc.ncbi.nlm.nih.gov/articles/PMC4592931/
Expert Panel on Neurological Imaging, Ortiz AO, Levitt A, Shah LM, et al. ACR Appropriateness Criteria® Suspected Spine Infection. J Am Coll Radiol. 2021;18(11S):S488-S501. https://pubmed.ncbi.nlm.nih.gov/34794603/
Spondylodiscitis. Radiopaedia.org. https://radiopaedia.org/articles/spondylodiscitis