Fluoroscopic evaluation of the cranial spread of contrast medium after sacrococcygeal or lumbosacral epidural injection in feline cadavers: a randomized noninferiority study.

The sacrococcygeal epidural approach achieves comparable cranial spread to lumbosacral injection in cats at equivalent volumes.

This prospective, randomized, cadaveric noninferiority study compared cranial epidural spread of contrast medium following lumbosacral (LS) versus sacrococcygeal (SCo) epidural injection in 26 feline cadavers. Three sequential volumes of nonionic iodinated contrast medium (0.015, 0.03, and 0.015 mL/cm occipital-coccygeal length) were injected epidurally, and fluoroscopic epidurography assessed cranial spread after each injection. Cranial spread was quantified by the number of vertebrae containing contrast, and circumferential distribution was also evaluated. A predefined noninferiority margin of two vertebral segments caudal to LS spread was used. Results demonstrated that noninferiority of the SCo approach was confirmed only after the cumulative third volume (approximately 0.6 mL/kg total). After volumes 1 and 2, median cranial spread was similar between groups (median difference = 0 vertebrae), but 95% confidence intervals included the noninferiority margin, precluding definitive noninferiority conclusions at those volumes. Increasing injected volume significantly increased cranial epidural spread regardless of approach (p < 0.0001). Intravascular contrast contamination occurred frequently in both groups (61.5% LS; 69.2% SCo; p = 0.688), highlighting a common technical challenge. Two intrathecally injected cadavers served as anatomical comparisons. The authors conclude that with equivalent injection volumes, the SCo approach achieves cranial epidural spread comparable to the LS approach in feline cadavers, and may represent a viable alternative to LS epidural injection in cats, particularly when LS access is challenging.

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