Mucocele of the Paranasal Sinus

A paranasal sinus mucocele is a slowly expanding, mucus filled cystic lesion lined by sinus mucosa, caused by obstruction of the sinus drainage. It erodes the bony walls and can invade the orbit and the skull base.

It is most often in the frontal (60%) and ethmoid (25%) sinuses, then maxillary and sphenoid. It presents at 40 to 60 years, with no sex difference. Causes are previous sinus surgery, trauma, chronic sinusitis, polyps, tumours and fibro osseous lesions.

Pathophysiology.

Blockage of the sinus ostium traps secretions and desquamated epithelium. Pressure and bone resorption by inflammatory mediators (prostaglandins, interleukins) enlarge the sinus over years.

Frontal or retro orbital headache, proptosis, displacement of the eye, diplopia, reduced vision, a forehead or medial canthus swelling, and nasal blockage. Sphenoid mucocele causes visual loss or cranial nerve palsy.

Red flags.

• Sudden visual loss.
• Ophthalmoplegia.
• Cerebrospinal fluid leak or neurological deficit.
• Fever and pain (infection into pyocoele).

CT of the sinuses shows a smooth, expansile, homogeneous mass with bone thinning or erosion and no enhancement. Magnetic resonance imaging distinguishes it from tumour (variable signal depending on protein content, rim enhancement only), and defines orbital and intracranial extension. Ophthalmology review documents visual function.

Differential diagnosis.

• Pyocoele.
• Sinonasal tumour.
• Encephalocele.
• Dermoid or epidermoid cyst.
• Fibrous dysplasia.
• Inverted papilloma.

Endoscopic marsupialisation (wide drainage into the nose) is the treatment of choice and has a recurrence rate of under 10%. Open or osteoplastic approaches are for frontal lesions that are not accessible endoscopically. There is no drug therapy for the mucocele itself.

• Saline irrigation: 240 mL isotonic saline into each nostril twice daily for 4 to 8 weeks after surgery; monitor crusting; use boiled or sterile water.
• Mometasone nasal spray 50 micrograms for each spray (after surgery): 2 sprays into each nostril once daily for 4 to 8 weeks; maximum 200 micrograms daily in each nostril; monitor for epistaxis.

If infection develops, give intravenous antibiotics and drain the sinus urgently.

Monitoring. Endoscopy at 2 weeks, 6 weeks, 3 months and 6 months; MRI at 12 months.

Referral and escalation. ENT, ophthalmology and neurosurgery for orbital or skull base extension.