Horner's Syndrome Caused by Ultrasound-Guided Supraclavicular Nerve Block.

Horner's syndrome, caused by supraclavicular nerve block, is a rare case. It is mostly expected after interscalene nerve block, caused by anatomic reasons. Horner's syndrome results from neuronal paralysis of the post-ganglionic cervical sympathetic chain. For anatomic reasons, interscalene nerve block is very common but very uncommon in the case of supraclavicular nerve block. Horner's syndrome results from the paralysis of the ipsilateral sympathetic cervical chain. One common cause is interscalene nerve block. This effect occurs frequently due to anatomical proximity - the brachial plexus nerves in the interscalene region are situated very close to the sympathetic cervical chain. When a local anesthetic is injected near the interscalene nerves, it can spread to surrounding tissues, including the sympathetic chain. In contrast, with a supraclavicular nerve block, this effect is extremely rare. The rarity is due to the anatomical distance between the supraclavicular nerves and the cervical sympathetic chain, as well as the presence of a thick fascial layer surrounding the supraclavicular nerves, which prevents the spread of local anesthetic to the upper tissues. In this case, the unusual effect of supraclavicular nerve block was revealed as a Horner's syndrome soon after injection of local anesthetic. There are a few reasons explaining this outcome. In one case, an anatomic-short neck can cause rapid distribution of local anesthetic through surrounding tissues. Another reason might be fat tissue, as local anesthetics are fat-soluble agents, and rapid injection of local anesthetics can be a reason for the upward distribution of medication. This case is important to understand what might be expected, even in cases when it is unusual, and inform the patient in advance to avoid any incomprehension after an operation.