Describe mucocele of the paranasal sinuses.

Mucocele of the Paranasal Sinuses

• A mucocele is a slowly expanding, epithelium-lined cyst filling a paranasal sinus with retained mucus, caused by obstruction of the sinus ostium.
• When it becomes infected it is a pyocele.
• It is histologically benign but behaves like a slow-growing tumour, eroding bone by pressure.
• The essential concept is that it is a benign lesion producing a malignant-like pattern of local destruction — and the mechanism is pressure, not invasion: continued mucus secretion into a closed cavity raises the pressure, causing bone remodelling, thinning and eventual erosion, with osteoclastic activity from released inflammatory mediators
• Sites, in order of frequency — the frontal sinus is by far the commonest (60%), then ethmoid, then maxillary and sphenoid.
• The frontal predominance follows from its long, narrow and tortuous drainage pathway through the frontal recess.
• Causes of ostial obstruction — chronic rhinosinusitis and polyps; previous surgery, particularly frontal or Caldwell-Luc procedures, which may present years or decades later; trauma with a fracture involving the drainage pathway; osteoma or other tumour; allergy; and cystic fibrosis
• Presentation is insidious and not with nasal symptoms.
• Frontal and ethmoid mucoceles — a painless swelling at the superomedial orbital rim, displacement of the globe downward, laterally and forward, proptosis, diplopia and epiphora; with frontal headache
• Egg-shell crackling may be felt on palpation of the thinned bone.
• Sphenoid mucocele is the dangerous one — it may cause visual loss from optic nerve compression, ocular palsies and retro-orbital headache, and is a treatable cause of blindness that is repeatedly missed because the nose looks normal
• Maxillary mucocele — cheek swelling and displacement of the orbital floor
• A pyocele presents acutely, with pain, fever, inflammatory signs and rapid progression, and a much higher risk of orbital and intracranial complications
• Imaging — CT shows a smooth, expanded, homogeneous, non-enhancing opacified sinus with thinned or eroded, remodelled bone; the smooth expansion and absence of enhancement distinguish it from a tumour
• MRI is used where the diagnosis is uncertain or intracranial extension is suspected; the signal varies with the protein content of the contents
• Treatment is surgical and the principle is marsupialisation, not excision
• Endoscopic marsupialisation — creating a wide, permanent opening into the nose so the sinus drains and ventilates — is now the standard treatment and has largely replaced external approaches