Pyocoele of the Paranasal Sinus

A paranasal sinus pyocoele is an infected mucocele, where the sinus is filled with pus and bone is eroded. It is more acute and painful than a mucocele and risks orbital and intracranial spread.

It arises from a pre-existing mucocele, usually frontal or ethmoid, and is more likely after sinus surgery, trauma or in immunocompromised patients. Organisms are Staphylococcus aureus, streptococci, Haemophilus influenzae and anaerobes.

Pathophysiology.

Bacteria colonise the obstructed mucocele and produce pus under pressure, which erodes the thin sinus walls and can break into the orbit or cranial cavity.

Fever, severe headache, tender swelling over the sinus, eyelid swelling, proptosis, pain on eye movement, reduced vision, and in advanced cases meningeal signs and seizures.

Red flags.

• Reduced vision or ophthalmoplegia.
• Severe headache, neck stiffness or confusion.
• Seizures or focal neurological signs.
• Sepsis.

CT with contrast shows an expanded sinus with rim enhancement and bone erosion. Magnetic resonance imaging identifies orbital and intracranial extension and abscess. Send blood cultures, full blood count and C-reactive protein, and culture the pus at drainage. Ophthalmology review documents visual function.

Differential diagnosis.

• Mucocele without infection.
• Acute sinusitis with orbital cellulitis.
• Pott puffy tumour.
• Sinonasal tumour with necrosis.
• Invasive fungal sinusitis.

Give intravenous antibiotics and drain the sinus urgently (endoscopic marsupialisation, or open drainage), and treat intracranial complications. Do not delay surgery for imaging if vision is threatened.

• Ceftriaxone: 2 g IV every 12 hours; maximum 4 g daily; 2 to 6 weeks depending on complications, then oral step down if clinically settled; monitor renal function, liver tests and blood counts; no routine renal adjustment.
• Metronidazole (with ceftriaxone): 500 mg IV or orally every 8 hours; maximum 1.5 g daily; monitor neuropathy and liver tests; reduce to 500 mg every 12 hours in severe hepatic impairment.
• Vancomycin (added for suspected MRSA): load 25 to 30 mg/kg IV, then 15 to 20 mg/kg every 8 to 12 hours; target area under the curve 400 to 600; monitor levels and creatinine; extend the interval in renal impairment.
• Co-amoxiclav (oral step down): 625 mg orally three times daily to complete 2 to 4 weeks in total; maximum 1.5 g amoxicillin daily; monitor liver tests, diarrhoea and rash; give 625 mg twice daily when creatinine clearance is 10 to 30 mL/min.

Monitoring. Visual acuity and neurological examination every 4 to 6 hours at first; endoscopy and imaging at 2 weeks.

Referral and escalation. ENT, ophthalmology and neurosurgery urgently.

Special groups. Children need weight based dosing: ceftriaxone 100 mg/kg daily (maximum 4 g).