Computed tomography assessment of the conus medullaris and dural sac termination in adult sheep

This study aimed to describe the termination of the conus medullaris (CM) and dural sac (DS) in sheep using computed tomography (CT) myelography. Forty-adult Merino-mixed sheep underwent CT imaging after a lumbosacral intrathecal injection of iodinated contrast. The vertebral level of CM and DS termination was recorded. The CM was visible in 28 animals and terminated at S1 in 14 (50 %; 95 % CI: 30.6-69.4 %) and at S2 in 14 (50 %; 95 % CI: 30.6-69.4 %). The DS was evaluable in 33 animals and ended caudal to the sacrococcygeal junction (Cd-SC) in 31 (93.9 %; 95 % CI: 79.8-99.3 %) and at the sacral level (SACR) in 2 (6.1 %; 95 % CI: 0.7-20.2 %). No terminations cranial to the lumbosacral space (Cr-LS) were observed. These findings have implications for neuraxial anaesthesia in sheep. The CM ends caudal to the lumbosacral space, and the DS often extends beyond the sacrococcygeal space. Careful site selection is essential to minimise the risk of iatrogenic spinal cord injury during lumbosacral or sacrococcygeal epidural injections.