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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.
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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.
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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
anterolateral ...