Ptosis is due to interruption of the sympathetic motor innervation of the superior tarsal muscle which is a small muscle composed of smooth muscle fibers intimately associated with the undersurface of levator palpebrae superioris muscle. This muscle inserts into the tarsal plate of the upper eyelid and controls eyelid elevation and retraction.
Horner syndrome can be anatomically classified into three types, depending on where the pathology affects the sympathetic pathway . Interestingly, postganglionic lesions do not tend to present with anhydrosis, as opposed to central or preganglionic lesions.
- central: involves the first order neuron that starts in the hypothalamus and descends down the brainstem to the level between C8 and T2
- preganglionic: involves the second order neuron that passes from the brainstem to the superior cervical ganglion in the neck
- postganglionic: involves the third order neuron that ascends along the internal carotid artery to enter the cavernous sinus, where it joins the ophthalmic division of the trigeminal nerve
There is an extremely long list of causes. The main ones include :
- hypothalamic, thalamic or brainstem
- ischemia (e.g. lateral medullary syndrome)
- apical lung mass/tumor (Pancoast tumor)
- cervical rib
- cervicothoracic spine
- brachial plexus injury
- thyroid mass/goiter/tumor
- mediastinal mass tumor
- common carotid artery pathology
- injury to superior cervical ganglion