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Chapter 24. Caudal Anesthesia

Which of the following anatomic structures is not part of the sacral canal?

A. Filum terminale

B. Conus medullaris

C. Spinal meninges

D. Cauda equine

B is correct. The conus medullaris is not part of the sacral canal, it is the tapered, lower end of the spinal cord, and it is found at lumbar vertebral levels 1 (L1) and/or 2 (L2). While it can occur at a lower level, it is not usually located within the sacral canal.

A is incorrect. The filum terminale is a delicate strand of fibrous tissue about 20 cm in length, proceeding downward from the apex of the conus medullaris. It runs along the sacral canal and its lowest margin emerges at the sacral hiatus and traverses the dorsal surface of the fifth sacral vertebra and sacrococcygeal joint to reach the coccyx, where it is referred to as the coccygeal ligament.

C is incorrect. Spinal meninges are part of the sacral canal. Near the midlevel of the sacral canal (typically the middle one-third of S2), the subarachnoid and subdural spaces cease to exist, and the lower sacral spinal roots and filum terminale pierce the arachnoid and dura maters.

D is incorrect. Cauda equina, including filum terminale, are part of the sacral canal.

Which of the following statements is true with regards to caudal anesthesia?

A. Success rates are higher in adults when compared to children.

B. It is easier to access the caudal canal of men when compared to women.

C. The cephalad flow of local anesthetic (LA) is less limited in lordotic patients with exaggerated lumbosacral angles, when compared to patients with more flattened lumbosacral angles.

D. LA injected into the caudal canal can easily egress through the anterior sacral foramina.

D is correct. The sacral foramina afford anatomical passages that permit the spread of injected solutions, such as LAs and adjuvants. The posterior sacral foramina are essentially sealed by the multifidus and sacrospinalis muscles, but the anterior foramina are unobstructed by muscles and ligaments, permitting ready egress of solutions through them.

A is incorrect. The adipose tissue content of the caudal canal is subject to an age-related decrease in its density. This change is thought to be responsible for the transition from the predictable spread of LAs administered for caudal anesthesia in children to the limited and unpredictable segmental spread seen in adults.

B is incorrect. The level ...

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