Cavernous Sinus Thrombosis
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Direct answer
The veins of the face have no valves, which is why a squeezed pimple on the upper lip can, days later, present with a proptosed, chemotic, painfully immobile eye — septic thrombosis of the cavernous sinus. Infection reaches the sinus retrograde along the angular and superior ophthalmic veins from the danger area (upper lip, nose, medial cheek), or via the pterygoid plexus from maxillary molar infections. The earliest localising sign is a lateral rectus palsy, because the abducens nerve runs free within the sinus lumen; management is admission, high-dose intravenous antibiotics, drainage of the primary source and urgent specialty co-care.
What you must remember
- Anatomy: the cavernous sinus is a paired dural venous sinus beside the sella turcica; its lumen carries the internal carotid artery — the only artery within a dural sinus — and the abducens nerve (CN VI).
- The lateral wall carries the oculomotor (III), trochlear (IV), ophthalmic (V1) and maxillary (V2) nerves from above down, while the abducens nerve and internal carotid artery run free in the lumen — abducens palsy is the earliest sign, and the five-structure list is every examiner's favourite.
- Routes: the valveless angular and ophthalmic veins from the danger area enter the sinus directly; maxillary molar and infratemporal infections reach it through the pterygoid plexus.
- Clinical picture: periorbital swelling progressing to proptosis, chemosis, painful ophthalmoplegia with diplopia, ptosis, dilated pupil, sensory loss in V1 and V2, papilloedema, high fever with rigors, meningism — with a notorious tendency to become bilateral through the intercavernous sinuses.
- Imaging: contrast-enhanced CT or MRI with venography — a filling defect in the sinus with a dilated superior ophthalmic vein; it also separates the condition from orbital cellulitis.
- Treatment: intravenous antibiotics for three to four weeks (for example ceftriaxone with vancomycin and metronidazole — Staphylococcus aureus is the commonest organism, so antistaphylococcal cover is mandatory), drainage of the dental or facial source, ophthalmology and neurosurgery involvement; anticoagulation remains controversial, decided case by case.
- Outcomes: blindness, meningitis, brain abscess and death — mortality remains significant at around a third of cases in many series.
- Prevention, the dental duty: never squeeze lesions of the danger area; treat maxillary canine and molar infections before they travel.
From lip to sinus — the pathway examined
Reconstruct the classical case: a 26-year-old squeezes an upper-lip furuncle; three days later that side of the face is swollen and the eye is proptosing. The furuncle drains to the angular vein, which anastomoses with the superior ophthalmic vein — both valveless, so straining and local pressure drive infected thrombus retrograde into the sinus. The expanding thrombus first embarrasses the abducens nerve — double vision on lateral gaze — before the lateral wall structures add ptosis, a sluggish pupil and numbness over forehead and cheek. The swollen superior ophthalmic vein and retro-orbital pressure produce the proptosis and chemosis; the intercavernous communication explains why the other eye can follow within a day. Distinguish it from orbital cellulitis: both swell the eye, but V1/V2 sensory loss, lateral rectus palsy, meningism and bilaterality point to the sinus. Then act: blood cultures, contrast CT or MR venography, intravenous antistaphylococcal therapy, drainage of the lip lesion or tooth, and a low threshold for lumbar puncture if meningism dominates. The moral sits in the first sentence: the furuncle was squeezed, and the face's valveless veins obliged.
Where students slip
Anatomy marks are lost in two places: forgetting that the abducens nerve and internal carotid run inside the lumen — the exam's favourite distractor — and misordering the lateral wall, which runs III, IV, V1, V2. Clinically, orbital cellulitis is the standard wrong answer to the vignette; the discriminators worth memorising are the V1/V2 hypoaesthesia, the lateral rectus palsy and the tendency to bilaterality. Students also underplay the dental route — maxillary molars reach the sinus through the pterygoid plexus — and the danger area must be drawn, not merely named: upper lip, nose, medial cheek.
Frequently asked questions
Which cranial nerve is paralysed earliest in cavernous sinus thrombosis?
The abducens (VI), because it runs through the sinus lumen itself; its palsy impairs lateral gaze and is often the first localising sign.
Name the structures in the lateral wall of the cavernous sinus.
From above downward: the oculomotor nerve, trochlear nerve, ophthalmic division (V1) and maxillary division (V2) of the trigeminal nerve.
Which artery passes through the cavernous sinus?
The internal carotid artery — the only artery to lie within a dural venous sinus, which is why sinus pathology threatens catastrophic haemorrhage or ischaemia.
How does an upper-lip infection reach the cavernous sinus?
Via the valveless angular and superior ophthalmic veins, allowing retrograde septic thrombophlebitis; maxillary molars reach it through the pterygoid plexus.
What imaging confirms the diagnosis?
Contrast-enhanced MRI or CT with venography, showing a filling defect in the cavernous sinus and a dilated superior ophthalmic vein.
Which organism is most frequently responsible?
Staphylococcus aureus in the great majority of septic cases, which is why antistaphylococcal intravenous cover is non-negotiable.