A 70-year-old female with a past medical history of atrial fibrillation, for which she takes rivaroxaban, and prior history of L4-L5 decompressive laminectomy presents with a one-year history of recurrent lower back pain with pain radiating to her bilateral lower posterior thighs. Magnetic resonance imaging (MRI) of the lumbar spine reveals severe central canal stenosis from scar tissue build-up (fibrosis). You opt to perform a caudal epidural steroid injection (ESI) for her radicular-type pain.

1. What are the reasons to consider a caudal epidural over other types of epidurals?

Caudal epidurals are effective for getting steroid into the lower spinal segments in those who have undergone lumbar laminectomy surgeries. This is because once the lamina is removed and scar tissue has formed, the epidural space is no longer free from resistance. Since the loss of resistance normally felt on a routine interlaminar epidural would no longer be present, the procedure cannot be done safely. Other considerations for a caudal epidural include poor visualization or difficult anatomical variants, such as poor transforaminal access due to foraminal stenosis or those with severe scoliosis.^1,2

2. Are these types of injections safe to use while patients are on anticoagulation?

This is a controversial subject. Per ASRA Pain Medicine guidelines,³ ESIs, including cervical, thoracic, lumbar, sacral, interlaminar, and transforaminal, are intermediate-risk category procedures. Therefore, determining whether anticoagulation should be held depends on the type of anticoagulation and individual facility guidelines. However, based on studies, caudal epidurals appear to have a lower risk of bleeding and spinal hematomas compared to interlaminar and transforaminal epidurals. Therefore, the risks and benefits should be discussed with the patient and the physician managing the anticoagulation.^3-6

3. What are relative or absolute contraindications to caudal ESIs? 

1. Congenital abnormalities of the dural sac, such as sacral meningocele, sacral spina bifida, or sacral perineural cysts
2. Visible pilonidal cyst identified on physical exam
3. Local malignancy
4. All the above

Answer: D. Contraindications for caudal ESIs include pilonidal cyst, systemic infection, or local skin infection near or around the sacrum region given the potential risk for hematogenous spread via Batson venous plexus and concern for epidural abscess formation. Another contraindication for caudal ESIs is congenital abnormality of the dural sac and its contents, such as sacral meningocele, sacral spina bifida, or sacral perineural cysts, which increase the risk for an inadvertent dural puncture during caudal ESIs. Other common contraindications include local malignancy and significant allergy to contrast, anesthetic, or steroid used in the procedure.^7,8

4. What are the contents of the sacral canal?

The sacral canal is formed by the sacral vertebral foramina and is shaped in a triangle fashion. The sacral canal contains the epidural venous plexus, cauda equina including filum terminale, spinal meninges, and adipose tissue.⁸

5. What is the average volume of fluid used to complete transforaminal steroid injections, interlaminar ESIs, and caudal ESIs?

Match the correct procedure with the estimated volume. 

a. Lumbar transforaminal steroid injections
b. Lumbar interlaminar ESIs
c. Caudal ESIs

i. An average volume of 1-2 ml of fluid
ii. An average volume of 15-25 ml of fluid
iii. An average volume of 6-10 ml of fluid

A = i, B = iii, C = ii

The average volume of the sacral canal, once all contents have been removed in dried bone specimens, is around 34 ml. A small study involving MRI of the sacrum estimated an average sacral canal volume of 14.4 mL excluding the foramina and dural sac. The large capacity of the sacral canal results in significantly larger volumes of fluid needed. Typically, caudal ESIs may require 20-25 ml of fluid to reach their intended level of treatment. The third lumbar vertebrae is considered the median segmental level reached with 20 to 25ml of fluid injected into the caudal space in a prone patient. This is in comparison to lumbar transforaminal ESIs, which typically require 1-2 ml of fluid, and lumbar Interlaminar ESIs, which typically require 6 to 10 ml of fluid.^8,9 

6. What complications should be considered with this increased volume of fluid used to complete caudal ESIs? 

a. Increased risk of seizure or local anesthetic systemic toxicity
b. Increased risk of retinal hemorrhage or transient blindness
c. A and B

Answer: C. A potential complication of caudal ESI includes an increased risk of seizures compared to thoracic and lumbar ESIs. The suspected mechanism of action for this complication is the result of inadvertent intravascular uptake of local anesthetic via the epidural venous plexus in combination with increased volume of local anesthetic used to complete the procedure. Typically, the epidural venous plexus is located anteriorly in the sacral canal and commonly ends around S4. In some cases, the epidural venous plexus may continue more caudally. Careful aspiration and observation are helpful to avoid this complication. In addition, on rare occasions, large volume caudal ESIs have resulted in complications such as increased intraocular pressure resulting in retinal hemorrhage or transient blindness.⁸

7. What additional potential complications are associated with caudal ESIs? 

• A potential complication of caudal ESI is needle malposition or needle misplacement in the sacral periosteum. The cortical layer of the sacral periosteum is known to be relatively thin. This complication can be identified by considerable pain and resistance with needle advancement and injection. Another common complication of caudal ESI is the misplacement of the needle outside of the sacral canal. Should this complication occur, palpation will reveal crepitus and fluid build-up of the tissues overlying the sacrum.^{7, 8}
• In addition, patients with a history of urinary retention should be counseled pre-procedure about the possibility of worsening urinary retention due to blockage of the sacral nerve roots.⁸

8. What contrast-flow patterns are found with fluoroscopically guided caudal ESIs?

• After the needle placement is confirmed in a lateral view, the needle can be directed up to, but not higher than, the S3 level to avoid dural puncture. Contrast agent is then injected and can be visualized in the lateral and anteroposterior (AP) views. As the contrast spreads through the epidural fat, this produces an irregular appearance. A “Christmas-tree” like appearance can be visualized in the AP view as the contrast spreads caudally around the dura mater and nerve roots.^1,10
• If the contrast agent is flowing primarily in a dorsal direction, localizing to the asymptomatic side, or spilling out of the foramina, the needle should be redirected in the AP view and additional contrast agent should be injected with visualization of optimal spread. Additionally, after the medication has been injected, a post-injectate radiograph may be obtained and distal spread of contrast may be visualized throughout the sacral and lumbar epidural space.¹

9. What are the benefits of fluoroscopic-guided versus ultrasound-guided caudal ESIs? 

• Fluoroscopically guided caudal ESIs are more efficacious than palpation-guided injections, even when a patient has an easily palpable sacral hiatus. Direct visualization with fluoroscopy allows for correct needle placement into the sacral hiatus, and this can be verified with both a lateral and AP view. This method allows for careful placement up to, but no higher than, the S3 level to avoid the dural sac. Another benefit of using the fluoroscope is direct visualization of injected contrast in multiple views to ensure that the medication is spreading caudally and possibly even spreading to the more symptomatic side.¹
• Ultrasound-guided caudal ESIs offer an alternative method for injection with several added benefits. Using ultrasound, the sacral hiatus can be visualized and the needle can be directed into the epidural space and may allow for faster needle placement than fluoroscopically guided caudal injections. Doppler flow can be used to avoid intravascular flow, and drug spread can be visualized with increased hypoechogenicity. Additionally, ultrasound allows for avoidance of radiation exposure as well as contrast agent.^1,11,12

References

1. Furman MB. Atlas of Image-Guided Spinal Procedures. 2^nd ed. Philadelphia, PA: Elsevier, Inc.; 2018
2. Kao SC, Lin CS. Caudal epidural block: an updated review of anatomy and techniques. Biomed Res Int. 2017; 9217145. https://doi.org/10.1155/2017/9217145.
3. Narouze S, Benzon HT, Provenzano D, et al. Interventional spine, and pain procedures in patients on antiplatelet and anticoagulant medications (second edition): guidelines from the American Society of Regional Anesthesia and Pain Medicine, the European Society of Regional Anaesthesia and Pain Therapy, the American Academy of Pain Medicine, the International Neuromodulation Society, the North American Neuromodulation Society, and the World Institute of Pain. Reg Anesth Pain Med. 2018;43(3):225-62. https://doi.or/10.1097/AAP.0000000000000700.  
4. Common contraindications and blood thinner management for pain management interventional procedures. The Procedure Guide. Available at: https://theprocedureguide.com/common-contraindications-and-blood-thinner-management-for-pain-management-procedures/ Accessed February 7, 2022.
5. Kaye AD, Manchikanti L, Novitch MB, et al. Responsible, safe, and effective use of antithrombotics and anticoagulants in patients undergoing interventional techniques: American Society of Interventional Pain Physicians (ASIPP) Guidelines. Pain Physician. 2019;22(1S):S75-S128.
6. Simon JI, Gehret J, Larsen ES, et al. Caudal epidural steroid injections in the setting of remaining on antithrombotics: a retrospective study. Pain Physician. 2021;24(6):E821-E828.
7. Candido KD, Nader A. Caudal anesthesia. In Benzon HT, Raja SN, Molloy RE, et al. (Eds.) Essentials of Pain Medicine and Regional Anesthesia. 2nd ed. Philadelphia, PA: Elsevier-Churchill Livingstone; 2005. 
8. Waldman SD. Caudal epidural block: prone position. In Waldman SD, Atlas of Interventional Pain Management. 5th ed. Philadelphia, PA: Elsevier; 2019. 
9. Cleary M, Keating C, Poynton AR. The flow patterns of caudal epidural in upper lumbar spinal pathology. Eur Spine J. 2011;20(5):804-7. https://doi.org/10.1007/s00586-010-1613-5
10. Chen CP, Tang SF, Hsu TC, et al. Ultrasound guidance in caudal epidural needle placement. Anesthesiology. 2004;101(1):181-4. https://doi.org/10.1097/00000542-200407000-00028
11. Park Y, Lee JH, Park KD, et al. Ultrasound-guided vs. fluoroscopy-guided caudal epidural steroid injection for the treatment of unilateral lower lumbar radicular pain: a prospective, randomized, single-blind clinical study. Am J Phys Med Rehabil. 2013;92(7):575-86. https://doi.org/10.1097/md.0000000000002261
12. Hazra AK, Bhattacharya D, Mukherjee S, et al. Ultrasound versus fluoroscopy-guided caudal epidural steroid injection for the treatment of chronic low back pain with radiculopathy: a randomised, controlled clinical trial. Indian J Anaesth. 2016;60(6):388-92. https://doi.org/10.4103/0019-5049.183391