Steven R Magidenko 1, Elodie E Huguet 1, Federico Vilaplana Grosso 1

Background
Pneumorrhachis, defined as gas within the vertebral canal, is a rare and often incidental finding in both human and veterinary medicine, with iatrogenic causes being the most common nontraumatic source. This study investigates the prevalence, anatomical distribution, and potential etiologies of pneumorrhachis and intraforaminal gas in dogs undergoing computed tomography (CT) angiography without known neurologic disease or trauma. The authors hypothesized these findings would be common, right-sided, and associated with intravenous catheter use, particularly due to gas migration into the vertebral venous system.

Methods
This retrospective study reviewed CT scans from 263 dogs imaged for thoracic, abdominal, or pelvic disease over one year. Dogs with recent trauma, neurologic signs, surgery, or infection were excluded. CT images were evaluated for the presence, laterality, and volume of pneumorrhachis and intraforaminal gas, which were subjectively graded. Catheter placement details, patient positioning, and post-scan complications were recorded. The relationship between catheter location and gas distribution was analyzed.

Results
Pneumorrhachis was identified in 19% of dogs, always when scanned in sternal recumbency. Gas was predominantly right-sided (76%), and its volume was mostly mild. In 26% of cases, gas volume increased in postcontrast images. Intraforaminal gas was present in all dogs with pneumorrhachis and followed a similar right-sided predilection. The presence of gas corresponded with the side of brachial vasculature catheter placement, and in some cases, gas could be traced anatomically into the vertebral venous plexus. No dogs showed neurologic signs within 24 hours post-CT.

Limitations
Limitations include the retrospective design and subjective assessment of gas volume. Variability in imaging timing and lack of delayed-phase imaging may have impacted detection. Patients scanned in non-sternal positions were few, limiting comparative analysis. The study also did not quantify gas volumes volumetrically, and exclusion of dogs with intervertebral disc disease limits generalizability.

Conclusions
Pneumorrhachis and intraforaminal gas are incidental, non-clinically significant findings commonly observed on CT in dogs undergoing contrast imaging, likely due to iatrogenic gas introduction through peripheral IV catheters. The right-sided predilection may relate to azygous vein anatomy and patient positioning. Awareness of these patterns may prevent misinterpretation of these findings as pathologic.

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