Is the Stellate Ganglion Part of an Interscalene Block?
No, the stellate ganglion is not intentionally targeted during an interscalene brachial plexus block, but it can be unintentionally affected as a complication when local anesthetic spreads medially beyond the intended injection site.
Anatomical Relationship and Unintended Involvement
The stellate (cervicothoracic) ganglion is anatomically separate from the brachial plexus but lies in close proximity in the neck region:
The stellate ganglion is located anterior to the neck of the first rib and anterior to the transverse process of C7, positioned medially to the brachial plexus structures 1, 2
The interscalene block targets the C5 and C6 nerve roots (or superior trunk) in the groove between the anterior and middle scalene muscles at approximately the level of the cricoid cartilage 3
Gray rami communicantes connect the stellate ganglion to the C6, C7, and C8 nerve roots, creating anatomical pathways for potential local anesthetic spread 2
Horner Syndrome as Evidence of Stellate Ganglion Block
When the stellate ganglion is inadvertently blocked during an interscalene procedure, it manifests as Horner syndrome:
Horner syndrome (ptosis, miosis, anhidrosis) is a recognized complication of interscalene blocks, occurring when local anesthetic spreads medially into the scalenovertebral triangle where the stellate ganglion resides 4
The supraomohyoidal block technique was specifically designed to prevent medial spread of local anesthetic beyond the lateral margin of the anterior scalene muscle, thereby avoiding stellate ganglion exposure 4
In cadaveric studies using the supraomohyoidal approach with lateral-directed needle advancement, the stellate ganglion was not exposed to injected solution, whereas traditional interscalene techniques resulted in medial spread that could reach the stellate ganglion 4
Clinical Distinction from Stellate Ganglion Block
The stellate ganglion block is a completely separate procedure with different indications:
Stellate ganglion blocks are performed for diagnostic, therapeutic, and prognostic purposes in conditions like complex regional pain syndrome (CRPS), not for surgical anesthesia 5, 6
The stellate ganglion block targets sympathetic structures specifically, whereas the interscalene block targets somatic sensory and motor fibers of the brachial plexus for shoulder anesthesia 7, 6
Common Pitfall to Avoid
The key pitfall is medially directed needle advancement during interscalene block, which increases the risk of stellate ganglion involvement and resultant Horner syndrome 4. Using ultrasound guidance with lateral and caudal needle direction (as in the supraomohyoidal approach) minimizes this unintended complication while maintaining effective brachial plexus blockade 4.