MRI Clues Unveiled: Early Signs of Spinal Surgery Infections in Dogs

Clinical presentation, magnetic resonance imaging characteristics, and short-term outcome of deep surgical site infection following thoracolumbar decompressive spinal surgery for intervertebral disc herniation in dogs

Alexandra Y. K. To, Giunio Bruto Cherubini, Abby Caine

Background

Intervertebral disc herniation (IVDH) is the most common spinal pathology in dogs and is often treated surgically through thoracolumbar (TL) decompression. While rare, deep surgical site infections (SSIs) pose serious complications. Human data suggest deep SSI rates around 0.8%, with limited veterinary-specific incidence data and diagnostic imaging criteria. This study aimed to define the clinical presentation, MRI features, and short-term outcomes associated with culture-confirmed deep SSI following TL decompressive spinal surgery in dogs.

Methods

This was a retrospective, single-center, observational study of 1,723 dogs undergoing TL decompressive surgery between 2017–2021. Inclusion criteria were: confirmed TL IVDH diagnosis, postoperative MRI due to poor recovery, revision surgery, and culture-confirmed deep SSI. MRI images were reviewed by blinded specialists, and variables including spinal cord compression ratios, lesion lengths, and soft tissue changes were analyzed. Clinical data and treatment outcomes were collected.

Results

Nineteen cases of deep SSI (1.1% incidence) were identified. Most presented within 7 days post-surgery with spinal hyperesthesia (100%) and neurological deterioration (37%). MRI revealed fascial plane tracking (100%), bilateral epaxial muscle hyperintensity (67%), and multifocal signal voids (90%) as distinctive signs. Staphylococcus spp. were the most common isolates. All dogs survived to discharge; 74% were ambulatory. At short-term follow-up, all re-evaluated dogs showed resolution of clinical signs.

Limitations

Key limitations included the retrospective design, small sample size, lack of a non-infected control group, and MRI protocol variability. Selection bias was introduced by requiring culture-confirmed infections, potentially excluding early or culture-negative cases. Additionally, the lack of standardized post-op imaging in healthy controls hindered discrimination of normal versus pathological MRI features.

Conclusions

Deep SSI is an uncommon but significant postoperative complication, typically presenting within two weeks of TL decompression surgery. MRI features such as fascial plane tracking and bilateral epaxial changes may help differentiate SSI from normal postoperative changes. Despite the severity, outcomes were generally favorable with appropriate intervention. These findings support the utility of MRI in early diagnosis and management and highlight the need for prospective studies with standardized protocols.

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