There are two kinds of neurons involved in the transmission of any signal through the sympathetic nervous system: pre-ganglionic and post-ganglionic. Sympathetic preganglionic neurons are located in the intermediolateral column of the spinal cord from T1 to L2. These neurons then leave the spinal canal as myelinated neurons on the ventral nerve root and travel to the thoracic paravertebral ganglia. These are paired ganglia on the anterolateral surface of the vertebrae. Embryologically, paired ganglia are formed for every vertebral level, but during development sequential ganglia can fuse, particularly in the cervical region. Preganglionic neurons can synapse at the same paravertebral ganglion level that they enter, or they can ascend or descend before synapsing. Postganglionic neurons with their soma in the paravertebral ganglia then track toward their target organs. Some presynaptic neurons pass through the paravertebral ganglia forming splanchnic nerves which synapse in prevertebral ganglia. Postganglionic neurons with their soma in the prevertebral ganglia then track toward their target organs.1 The ganglia include not just the sympathetic trunks but also: the cervical ganglia (superior, middle and inferior, which send sympathetic nerve fibres to the head and thorax organs), the celiac and mesenteric ganglia (which send sympathetic fibres to the gut), superior hypogastric plexus which send sympathetic nerve fibres to the lower abdomen and pelvis) and ganglion impar formed from two pelvic sympathetic trunks at the end on the front of the coccyx (which innervates sympathetically annus and coccygeal region).
There are many mechanisms of pain in cancer patients and sympathetic nervous system is often involved.2 The sympathetic nervous system can be blocked at the level of the ganglia or anywhere along a sympathetic pathway. Sphenopalatine plexus (mixed sympathetic-parasympathetic) block and neuroablative techniques- for pain caused by tumours of head region.5 Upper thoracic splanchnic nerve block or ablative techniques- for brachial plexopathies (caused for example by upper lung tumours), post mastectomy pain syndrome stellate ganglion block, head pain syndromes.4 For patients with pain caused by visceral tumours many effective interventions in the sympathetic nervous system is available. Coeliac plexus block or neurolysis- for upper abdominal pain caused by pancreatic head tumour,3 lymphadenopathy, gastric or hepatic tumour. Alternatively in patients with tumours of the epigastrium splanchnic nerves block, neurolysis and ablative techniques may be considered . Lumbar sympathetic block and ablative techniques- for lower extremity plexopathies (pelvis tumours), postradiation plexopathy6 and tumour-related bladder spasms.7 Superior hypogastric plexus block and neurolytic techniques- for pain caused by malignancies in the pelvic viscera.1 Ganglion impar block, RF ablation and neurolysis- for rectal tumour pain.1
All described interventions can be effective if the patient is properly qualified. For extremity or facial pain sympathetic nervous system blocks or ablative techniques are more efficient if there are symptoms of a disorder of the vegetative system like skin temperature changes, skin colour changes, oedema or disturbed sweating. In patients with visceral malignancies if the tumour directly presses the structure of the sympathetic nervous system (coeliac plexus compression in pancreatic tumour) causing difficult to treat pharmacologically visceral pain – interventions should be considered as soon as possible to avoid central sensitization. Contraindications for interventions on the sympathetic nervous system include- platelets level below 50–100k (depending on procedure), coagulopathies and inflammation at the injection site.
Amitabh Gulati, Vinay Putanniach, Bran M. Bruel, William S. Rosenberg, Joseph C. Hung; Essentials of Interventional Cancer Pain Management; Springer, 2019, p-149.
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