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Sympathetic blocks are widely employed for both diagnostic and therapeutic purposes. Kappis originally used paravertebral sympathetic blocks1 as treatment for severe pain and visceral pain syndromes. Mandl2 first introduced percutaneous interruption of the sympathetic chain in the early 20th century, and for many years thereafter it was a mainstay therapy for vascular insufficiency of the lower extremities. Current indications for sympathetic blocks include diagnosis of sympathetically maintained pain, treatment of neuropathic pain states such as acute herpes zoster, post-herpetic neuralgia, or other sympathetically maintained pain syndrome (reflex sympathetic dystrophy or causalgia, also known as complex regional pain syndrome), and management of ischemic pain. Sympathetic blocks are also used to help differentiate somatic from sympathetic pain origins. Pain syndromes responsive to initial sympathetic blocks are then treated with repeated blocks or followed up with surgical, chemical, or radiofrequency sympathectomy.

A good working knowledge of the sympathetic nervous system helps to understand how various neuraxial, plexus, and regional blocks can achieve sympathectomy. Descending autonomic projections from the hypothalamus, the oculomotor (Edinger-Westphal) complex, the locus ceruleus, and the nucleus of the solitary fasciculus terminate in the ipsilateral intermediolateral cell column in thoracic and upper lumbar spinal cord segments. Within this cell column lie the cell bodies of the preganglionic sympathetic neurons. Axons from these preganglionic cells exit the spinal cord by the anterior spinal roots and white rami communicantes to the sympathetic chain ganglia located along the left and right anterolateral margins of the spinal column. Upon reaching these paravertebral ganglia, the preganglionic sympathetic axons may synapse, pass cephalad or caudad for variable distances within the sympathetic chain before synapsing, or continue uninterrupted to a more distant ganglion or plexus, such as the celiac or hypogastic plexus. The nerves that bypass paravertebral sympathetic chain ganglia to more distant ganglia are called splanchnic nerves. Splanchnic nerves are the primary sympathetic fibers that innervate visceral organs. The ganglia in which they synapse are typically located near the respective organs that they innervate. Post-ganglionic sympathetic fibers then course along peripheral nerves or blood vessels to converge on specific organs. Once it is understood that the preganglionic sympathetics have spinal origins, and that the spread of sympathetic nerves occurs along blood vessels and peripheral nerves, it becomes easier to understand how sympathectomies can be performed not only through blockade of specific chain ganglia, but through a various number of neuraxial and regional block techniques.

Knowing the position of the sympathetic chain relative to somatic nerves helps to predict some of the side effects associated with the various sympathetic blocks. The sympathetic chain ganglia extends from the second cervical vertebra to the coccyx. In the cervical and thoracic region, these ganglia lie anterior to the base of the transverse processes or the head of the ribs; therefore they lie in close proximity to the somatic nerves. However, as the sympathetic chain courses caudally toward the lumbar region, it becomes more ...

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