Scheme showing sympathetic and parasympathetic innervation of the pupil and sites of a lesion in<unk> .<unk>  is usually acquired as a result of disease, but may also be congenital (inborn, associated with heterochromatic iris) or iatrogenic (caused by medical treatment). In rare cases,<unk>  may be the result of repeated, minor head trauma, such as being hit with a soccer ball. Although most causes are relatively benign,<unk>  may reflect serious disease in the neck or chest (such as a Pancoast tumor (tumor in the apex of the lung) or thyrocervical venous dilatation). Causes can be divided according to the presence and location of anhidrosis: * Central (anhidrosis of face, arm and trunk) * Syringomyelia * Multiple sclerosis * Encephalitis * Brain tumors * Lateral medullary<unk>  * Preganglionic (anhidrosis of face) * Cervical rib traction on stellate ganglion * Thyroid carcinoma * Thyroidectomy * Goiter * Bronchogenic carcinoma of the superior fissure (Pancoast tumor) on apex of lung * Klumpke paralysis * Trauma - base of neck, usually blunt trauma, sometimes surgery. * As a complication of tube thoracostomy * Thoracic aortic aneurysm * Postganglionic (no anhidrosis) * Cluster headache - combination termed Horton's headache * An episode of<unk>  may occur during a migraine attack and be relieved afterwards * Carotid artery dissection/carotid artery aneurysm/trauma * Cavernous sinus thrombosis * Middle ear infection * Sympathectomy * Nerve blocks, such as cervical plexus block, stellate ganglion or interscalene block
Horner's syndrome
Pilotto syndrome
Nance–Horan syndrome
Erb's palsy
Brown's syndrome
Summer penile syndrome
Bell's palsy
Frey's syndrome