Case 22 - Asymmetric pupils
What is the lesion?
The sympathetic plexus is outside the carotid artery, so carotid atherosclerosis - a major risk factor for ischaemic stroke and TIA - doesn't lead to Horner's. Only diseases of the carotid that cause it to expand laterally will - or alternatively pathology affecting it from the outside, for example in the carotid sheath or within the cavernous sinus.
The relevant pathologies to consider are dissection, aneurysm, or one of four core cavernous sinus pathologies: artery-to-sinus fistula, sinus thrombosis, inflammation or mass lesion.
The best fit here is dissection. The story began as pain in the neck and up the head during exercise, an important trigger - although not all dissection is preceded by an identifiable trigger. Horner's was noted that evening, but was probably there from the start - it just became more obvious while looking in the mirror in low light. Then a TIA happened in the following days - this is typical. The risk is highest in the first few days, but not usually at the exact time of the dissection - in cases where this can be established due to the presence of pain, the subsequent TIA/stroke often follows in the next few days. Of course, some dissections are painless, and we can't tell the onset - they are found only after a TIA/stroke leads to their detection on angiography, and if not for the TIA/stroke, they might never have been found at all!
Dissection causes the following features: pain, embolic complications, disruption of the sympathetic chain, and compression of adjacent cranial nerves - either in the carotid sheath or the cavernous sinus. In some patients, only some, or only one, of these features will be present - and pain may be absent. Sometimes dissection is completely silent, too - discovered incidentally on imaging.
An aneurysm of the carotid, particularly in the cavernous portion, can also cause Horner's as well as other palsies. A ruptured aneurysm can cause sudden-onset pain, and exercise can trigger rupture - although there would probably be other features such as ophthalmoplegia, proptosis and chemosis - the typical triad of cavernous sinus lesions - not just Horner's.
Carotid-cavernous fistula can develop spontaneously, after head injury, and as a complication of venous thrombosis or an aneursymal rupture. Auscultating the eyeball with a stethoscope can identify a bruit, indicating high-pressure flow through the fistula. It tends not to present suddenly like this, and as with aneurysm there are usually other features - the triad above - so an isolated Horner's is not suggestive.
Cavernous sinus thrombosis causes headache, and some or all of the triad above. The ophthalmoplegia may be complete, or partial, involving only some of the nerves. It's unusual for cavernous sinus thrombosis to just cause Horner's without affecting other nerves. It also tends to happen in people with serious head and neck infections, critical illness or thrombophilias - it's not usually seen in people who are otherwise well. Finally, it would also be unusual for this to lead to a cerebral TIA - stroke/TIA are sometimes seen when cavernous sinus lesions compromise the carotid (e.g. from compression or fistula) but this is unusual.
The cavernous sinus can be affected by inflammatory lesions, including Tolosa-Hunt syndrome - granulomatous inflammation in the sinus and orbit. This causes intense pain, but it is not usually sudden-onset. Opthalmoplegia is also present, which this patient doesn't have, and it doesn't cause TIA. A cavernous mass is also unlikely to present with the sudden-onset of pain or lead to TIA.
Dissection sounds very likely here. It's important to identify this rapidly in order to prevent a stroke - he's already had one TIA which is a very serious 'warning shot'.
Clinical formulation