Free ABA Advanced Exam Practice Question

The Answer and Explanation

Did you get it right? The correct answer is B.

In this patient with complex regional pain syndrome of the lower extremity, a lumbar sympathetic plexus (autonomic) block may offer significant pain relief. A trial is first performed with local anesthetic injection at the lumbar sympathetic plexus located at the anterolateral aspect of the lumbar vertebral bodies (L1-L5).

The lumbar sympathetic plexus comprises three to five ganglia and provides sympathetic innervation to the pelvis and lower extremities. The ganglion may be a single fused and elongated structure or composed of up to six separate ganglia from L1 to L5. In many patients, the first and second lumbar sympathetic ganglia are often fused. The lumbar sympathetic plexus is located at the anterolateral margin of the lumbar vertebral bodies and anterior to the psoas muscle (see the figure below). The plexus is located posterior to the vena cava on the right side. On the left side, it is lateral and slightly posterior to the abdominal aorta.

Abbreviation: IVC, inferior vena cava.

If the needle is advanced too deep, there is potential for intravascular injection into the vena cava, aorta, or lumbar vessels. There is also a risk of inadvertent somatic nerve block from the lumbar plexus, especially the genitofemoral nerve. If paresthesia from a lumbar paravertebral nerve is elicited, the needle should be withdrawn and redirected more cephalad. The proximity of the injection site to the peritoneal cavity also makes damage to the abdominal viscera possible. If the needle insertion site is too medial closer to the spinous process, it may result in epidural, subdural, or intrathecal injection and pose a risk of damaging the intervertebral disc, spinal cord, and nerve roots.

It is proposed that the sympathectomy from a lumbar sympathetic plexus blockade may improve regional blood flow to the following regions with circulatory insufficiency. Indications for a lumbar sympathetic block comprise three major clinical categories:

• Disorders of lower extremity circulatory insufficiency:
  • Arterial embolism
  • Thromboangiitis
  • Atherosclerosis
  • Raynaud phenomenon
  • Frostbite
• Nonvascular diseases:
  • Complex regional pain syndrome
  • Phantom limb pain
  • Postherpetic neuralgia
  • Renal colic
  • Analgesia for the first stage of labor
• Nonpainful causes:
  • Lower extremity hyperhidrosis

In all conditions, the block is first performed with a local anesthetic for diagnostic and predictive purposes before neurolysis (eg, radiofrequency ablation, chemical neurolysis) or surgical sympathectomy.

Incorrect Answer Explanations

Answer A: Injection 2-3 inches anterior to the lumbar vertebral body (L2) is too anterior and increases the risk of injuring anterior structures, including the abdominal aorta, inferior vena cava, or colon.

Answer C: Injection at the T12 level of the vertebral body is too cephalad and will not target the lumbar sympathetic ganglion.

Bottom Line:

A lumbar sympathetic plexus block may offer significant pain relief to patients with lower extremity complex regional pain syndrome, phantom limb pain, postherpetic neuralgia, renal colic, and analgesia for the first stage of labor. The correct needle position at the lumbar sympathetic plexus is at the anterolateral aspect of the lumbar vertebral bodies (L1-L5). Due to the high rate of successful block, the best approach is just cephalad to the middle of the L3 vertebral body.