Coexisting harlequin and Horner syndromes after high thoracic paravertebral anaesthesia.

A patient undergoing left mastectomy and immediate latissimus dorsi breast reconstruction under combined paravertebral block and general anaesthesia developed transient, well-demarcated, right-sided hemifacial erythema and sweating, and left-sided Horner syndrome postoperatively. This "harlequin" appearance occurs because of a normal or excessive vasodilatory, thermoregulatory response to heat or emotion mediated by an intact sympathetic pathway on the erythematous side, together with relative pallor of the pharmacologically blocked side.