Mucoceles are accumulations of mucus in obstructed paranasal sinuses that cause pressure necrosis of sinus walls and bone erosion of the inner sinus wall with new bone formation. They most commonly occur in the frontal and ethmoidal sinuses. Imaging shows an opacified sinus with mucoid or soft tissue density that may be hyperdense if low in water or colonized by fungi. There is bone expansion and the bone may be focally absent with a thin peripheral rim of expanded bone. Mucoceles are non-enhancing lesions and extensive peripheral enhancement raises concern for a mucopyocele or neoplasm.

1. Paranasal sinus
mucocele
Imaging findings

2. due to mucus secretion into chronically obstructed sinus
accumulated secretions cause pressure necrosis of sinus walls
with bone erosion of inner sinus wall and new bone formation
> 90% frontal + ethmoidal

3. histologically indistinguishable
from polyps and retention cysts

4. opacified sinus
with mucoid or soft tissue density
hyperdense if low water or fungal colonization
bone expansion
bone may be focally absent
look for thin peripheral rim of expanded bone
nonenhancing
with extensive peripheral enhancement think of mucopyocele
with central enhancement favor neoplasm

5. bone CT may be sufficient if small mucocele
 look for cause of sinus obstruction
chronic inflammation
prior trauma, surgery
neoplasm
if large expansile lesion, perform CE MRI

6. DDX expansile sinus lesions
mucocele
most common expansile lesion of paranasal sinuses
sinonasal polyposis
alergic fungal rhinosinusitis
antrochoanal polyp
sinonasal neoplasm

7. Remember
most common paranasal sinus
expansile lesion