The stellate ganglion is a small, star-shaped cluster of nerve cells located low in the neck, on either side of the windpipe. It functions as a relay station within the sympathetic nervous system, a major part of the autonomic nervous system responsible for controlling involuntary functions, including the “fight-or-flight” response. The ganglion transmits signals that regulate automatic processes in the head, neck, and upper extremities. Its activity can be temporarily interrupted through a medical procedure called a stellate ganglion block (SGB), which is used to treat certain chronic pain and psychological conditions.
Anatomy and Connection to the Sympathetic Nervous System
The stellate ganglion, also called the cervicothoracic ganglion, is a fusion of two smaller ganglia: the inferior cervical ganglion and the first thoracic ganglion. This structure is situated near the base of the neck, typically at the level of the seventh cervical vertebra (C7) and the first thoracic vertebra (T1).
Its location places it just in front of the neck of the first rib and behind the subclavian artery. The ganglion is part of the sympathetic trunk, a chain of nerve tissue running alongside the spine. As a component of the sympathetic nervous system, it receives input from the spinal cord and sends out postganglionic fibers.
These fibers supply sympathetic innervation to the head, neck, upper chest, and arms. Since virtually all sympathetic outflow to these upper regions passes through this single cluster of cells, its location makes it a practical target for medical interventions seeking to temporarily modulate the sympathetic nervous system.
Physiological Functions
The stellate ganglion relays signals that maintain homeostasis across the upper body, primarily regulating blood vessel and sweat gland activity. It exerts strong vasomotor control, regulating the constriction and dilation of blood vessels in the upper limbs, face, and head. This regulation is important for controlling blood flow.
The ganglion also governs sudomotor control, regulating sweat glands in the upper extremities and head. Furthermore, it provides sympathetic innervation to the eye, helping maintain the normal size of the pupil and the positioning of the eyelid.
Temporary interruption of the ganglion’s function causes a set of physical signs known as Horner’s syndrome. These signs include a constricted pupil (miosis), a drooping eyelid (ptosis), and decreased sweating on the affected side of the face and neck (anhidrosis). These temporary effects are a direct result of the sympathetic signals being blocked.
The Stellate Ganglion Block Procedure
The Stellate Ganglion Block (SGB) involves injecting a local anesthetic near the nerve cluster to temporarily disrupt its signaling. The patient lies on their back while the skin on the neck is cleaned and numbed. The medication, typically bupivacaine or ropivacaine, is injected through a thin needle near the C6 or C7 vertebrae.
Physicians rely on advanced imaging guidance, such as ultrasound or fluoroscopy (real-time X-ray), to ensure safety and precision. This imaging allows the provider to visualize surrounding blood vessels and confirm the exact placement of the needle tip. Once positioned, the anesthetic solution is slowly administered, spreading around the ganglion.
The local anesthetic temporarily inactivates the nerve fibers, effectively blocking the transmission of sympathetic signals through the ganglion. This action temporarily “turns off” the sympathetic outflow to the head and upper body.
A successful block is immediately confirmed by the onset of Horner’s syndrome on the side of the injection. The appearance of a drooping eyelid, constricted pupil, and facial flushing indicates that the medication has effectively reached and blocked the stellate ganglion.
Primary Clinical Applications
The SGB procedure is used for a variety of conditions, primarily those involving an overactive sympathetic nervous system. One of its longest-standing applications is treating Complex Regional Pain Syndrome (CRPS) in the head, neck, and upper extremities. CRPS involves chronic pain thought to be mediated by abnormal sympathetic nerve activity.
By blocking sympathetic signals, the SGB interrupts the pain cycle and reduces the excessive sympathetic drive contributing to CRPS. Patients with conditions such as refractory angina, severe peripheral vascular disease, and certain vascular headaches may also benefit from the improved circulation resulting from the sympathetic nerve interruption.
More recently, the SGB has gained attention for treating certain anxiety and trauma-related disorders, particularly Post-Traumatic Stress Disorder (PTSD). Blocking the stellate ganglion may decrease norepinephrine levels and reduce nerve signaling to brain regions like the amygdala, which are overly activated in trauma disorders.
Clinical evidence suggests that the SGB can significantly reduce PTSD symptoms like hypervigilance, anxiety, and poor sleep quality in some patients. This demonstrates its role in modulating the overall balance of the autonomic nervous system.