Carotid DissectionCarotid Dissection is a condition due to a tear or rent of the inner lining of the the carotid artery (the main artery carrying blood from your head to your heart- see diagram, courtesy of www.bartleby.com, creative commons license). It can occur out of the blue, or following what may have seemed to be fairly innocent trauma - such as a awkward fall e.g from steps or during sport. I have known arterial dissection to happen in a mum who sat with her neck craned at an angle for hours on end trying to bottle-feed her baby. It is controversial whether these are causes or co-incidences. The classic symptoms are pain in the neck, followed a few hours or days later by an episode of loss of vision, loss of speech or weakness. Some people will present with a proper stroke, and report neck or head pain at the same time. However, dissection of the carotid can present with severe headache and nothing else. In one series (from 1994), headache present from the outset, in addition to the stroke or TIA symptoms, in 59% of cases. The remaining cases presented with stroke or TIA without pain. In reports from the late 1990s it would be fair to say that about 4% of carotid dissection will have headache and headache alone. I suspect that with wider use of MRI brain scanning, the chance of finding dissection has increased and the numbers presenting with headache alone is higher still. The following might suggest that a severe headache is due to dissection of a carotid artery (after Boussier 1994):
You should note that pain in face, eye or neck is almost always on the same side as the actual tear in the carotid artery, whereas pain in the head is usually on the same side, but in 20% was on both sides. The cases reports generally say that pain of carotid dissection lasts for about 2 to 3 weeks, and according to the International Headache Society criteria, arterial dissection pain should resolve within a month. 
Other headache types associated with carotid dissectionThese headache presentations caused the doctors some difficulty in headache diagnosis, and must be rare. They are included so that you get a full picture of what can happen when there is arterial dissection of the carotid.
Horner Syndrome / Horners SyndromeThis is the only neurological sign associated with dissection in about 12% of cases (8/65 in Biousse series). Painful Horners Syndrome is a term which should immediately cause suspicion of internal carotid dissection. The reason for this is that the sympathetic nerves to the eye travel along the outside of the carotid artery. When the arterial dissection occurs, these sympathetic nerves are disrupted. The pupil of the eye loses its fight-and-flight response and shrinks (constricts). The eyelid loses about 30% of its nerve supply and falls slightly (no more than one or two millimetres below the limbus. The limbus is the point where the coloured part of the eye - iris - and the white of the eye - sclera meet at the 12 o'clock position. The lower eyelid is also partially paralysed, leading to slight elevation of the lower lid.Other clinical featuresOf course, stroke or TIA is the major symptom of carotid dissection, but I am restricting my discussion to headaches. Nausea and vomiting occurs in about 12% of cases, and about 50% of people with painful carotid dissection will have a previous history of migraine.Diagnosis of Carotid DissectionNeed I say it again - have a clinical suspicion that this is a potential diagnosis where if you treat early you could prevent a stroke.The best imaging is probably axial T1 weighted MRI of neck arteries, but MR angiography can also be excellent in skilled hands. Catheter angiography is often avoided, unless an intervention like stenting or coiling of a bulging pseudoaneurysm is being considered.
Angiography - carotid artery dissection
ReferencesB Guillon et al. Orbital pain as an isolated sign of internal carotid artery dissection. A diagnostic pitfall. Cephalalgia 1998;18:222-4 (Free Abstract only)V Biousse et al. Head pain in non-traumatic carotid artery dissection: a series of 65 patientsCephalalgia 1994;14:33-6 (Free Abstract only) Biousse V et al Pain as the only manifestation of internal carotid artery dissectionCephalalgia 1992;12:314-7 (Free Abstract Only) Nautiyal A et al. Painful Horner Syndrome as a Harbinger of Silent Carotid DissectionPLoS Med. 2005 January; 2(1): e19. (Full Free Text case report and literature review - illustrated).
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