Horner syndrome, also known as pediatric cervical sympathetic nerve palsy syndrome, has a complex cause. Any factor that causes sympathetic nerve damage in the neck and brainstem, such as trauma, surgery, tumors, inflammation, and vascular lesions, can cause this syndrome. Its manifestations are mainly seen in sympathetic nerve damage to the ipsilateral cervical sympathetic nerve, including dysfunction of the smooth muscles of the upper and lower eyelids, smaller eye fissures, and sunken eyeballs. There is also an absence of sweating along the ipsilateral side of the face, which is more pronounced in the acute phase, and some patients can develop contralateral facial flushing.