Congenital Horner's Syndrome
Horner's syndrome results from a defect in the sympathetic innervation to the eye and adnexal structures and causes an ipsilateral ptosis, miosis of the pupil and anhydrosis of the affected side of the face. The ptosis associated with Horner's syndrome is unique in that it results from Mueller's muscle inactivation as opposed to any sort of levator dysfunction.
Horner's syndrome is most commonly seen as an acquired condition in adults; less than 5% of cases can be classified as truly congenital. The most common cause of congenital Horner's syndrome is birth trauma resulting in a brachial plexus injury. Potentially life-threatening causes of congenital Horner's, including thoracic and cervical neuroblastoma, agenesis of the internal carotid artery and complications from perinatal surgical procedures have also been reported. Although less common, congenital Horner's resulting from carotid artery aneurysms and traumatic carotid dissection have also been described (Mirzai, 2006).
Ptosis secondary to a Horner's syndrome can usually be distinguished from isolated congenital ptosis because of the associated ocular and adnexal findings. Infants present with unilateral ptosis but also with associated miosis. Parents may report that the affected side of the face does not flush when the infant cries (so-called Harlequin baby'). In cases of congenital Horner's associated with sympathetic dysgenesis (and not birth trauma) the affected iris may be lighter, as iris melanocytes, like sympathetic ganglion cells, derive from neural crest cells.