cavernous sinus thrombosis
Summary
Cavernous sinus thrombosis (CST) is a rare, life-threatening condition caused by infection or clot formation within the cavernous sinus, most often secondary to spread of facial or sinus infections (the 'danger triangle'). It classically presents with headache, fever, periorbital edema, proptosis, chemosis, and ophthalmoplegia due to compression of cranial nerves III, IV, V1/V2, and VI.
Detail
The cavernous sinuses are paired dural venous sinuses located on either side of the sella turcica, draining blood from the orbits, superficial cerebral veins, and face via the ophthalmic veins and pterygoid plexus. Because facial veins lack valves, infections from the 'danger triangle' of the face (bridge of nose to corners of mouth), as well as sinusitis (especially sphenoid/ethmoid), orbital cellulitis, or dental infections, can spread retrograde into the cavernous sinus, causing septic thrombosis. Staphylococcus aureus is the most common causative organism, followed by Streptococcus species and anaerobes; fungal causes (e.g., Mucor, Aspergillus) occur in immunocompromised or diabetic patients (mucormycosis is classically associated with CST).
Anatomically, cranial nerves III, IV, V1, V2, and VI, along with the internal carotid artery, traverse the cavernous sinus, making them vulnerable to compression or inflammation. This produces the hallmark clinical picture: unilateral (often becoming bilateral) periorbital edema, proptosis, chemosis, ptosis, ophthalmoplegia (CN III, IV, VI palsies), and facial hypesthesia (CN V1/V2 distribution). Fever, severe headache, and signs of sepsis are typically present. Bilateral involvement occurs due to venous communication between the two cavernous sinuses.
Diagnosis is confirmed via contrast-enhanced MRI or CT venography showing a filling defect in the cavernous sinus. Blood cultures and CSF analysis (if lumbar puncture is safe) help identify the organism. Treatment requires urgent broad-spectrum IV antibiotics (covering MRSA), often combined with anticoagulation (though controversial), and management of the underlying infection source (e.g., sinus drainage). Antifungals are added if fungal etiology suspected. Complications include vision loss, stroke, meningitis, pituitary insufficiency, and death; mortality remains significant despite treatment.
Key Step 1/2 associations: dangerous triangle of the face, retrograde spread via valveless veins, association with sphenoid sinusitis, S. aureus as leading pathogen, and the classic triad of proptosis + chemosis + ophthalmoplegia.
Sources
- First Aid for the USMLE Step 1
- Harrison's Principles of Internal Medicine
- UpToDate: Cavernous sinus thrombosis
- Netter's Atlas of Human Anatomy
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