What is the most common cause of septic thrombophlebitis of the cavernous sinus?

Explanation

## Most Common Source of Cavernous Sinus Thrombophlebitis ### Epidemiology of Cavernous Sinus Infection **Key Point:** Ethmoid sinusitis is the most common paranasal sinus source of cavernous sinus thrombophlebitis, accounting for approximately 40–50% of cases. This is followed by sphenoid sinusitis (20–30%), frontal sinusitis (10–20%), and maxillary sinusitis (5–10%). ### Why Ethmoid Sinus? **Clinical Pearl:** The ethmoid sinus has direct anatomical proximity to the medial wall of the orbit and the ophthalmic veins, which drain directly into the cavernous sinus. Infection can spread rapidly along these venous channels without a significant barrier. **High-Yield:** The lamina papyracea (thin bony wall separating ethmoid sinus from orbit) is easily eroded by infection, allowing rapid spread to the orbit and subsequently to the cavernous sinus via superior and inferior ophthalmic veins. ### Comparative Risk by Sinus | Paranasal Sinus | Frequency | Reason for Risk | |---|---|---| | Ethmoid | 40–50% (highest) | Direct drainage to ophthalmic veins; thin lamina papyracea | | Sphenoid | 20–30% | Proximity to cavernous sinus; direct spread possible | | Frontal | 10–20% | Indirect route via diploic veins | | Maxillary | 5–10% (lowest) | Most distant from cavernous sinus | ### Clinical Presentation **Mnemonic: FEVER** — Fever, Edema (periorbital), Venous congestion (proptosis, chemosis), Extraocular muscle palsy, Retinal hemorrhage. ### Pathophysiology Ethmoid sinusitis → erosion of lamina papyracea → orbital cellulitis → thrombophlebitis of ophthalmic veins → cavernous sinus thrombophlebitis. **Warning:** Cavernous sinus thrombophlebitis is a medical emergency with mortality rates of 5–10% even with treatment, and up to 50% if untreated.