Paranasal sinus mucocoele

Paranasal sinus mucocoeles represent complete opacification of one or more paranasal sinuses by mucus, often associated with bony expansion due to obstruction of the nasal sinus drainage.

Clinical presentation depends on two factors:

  1. location and direction of expansion
  2. presence of infection

Mucocoeles distort local anatomy and exert pressure on adjacent structures as they enlarge. Examples include:

  • frontal mucocoele extending into the front of the orbit, presenting as a mass
  • posterior ethmoidal mucocoele compressing the orbital apex
  • sphenoidal mucocoele extending posteriorly impinging upon the pituitary and brainstem
  • maxillary mucocoele may elevate the orbital floor and result in proptosis

If a mucocoele becomes infected, clinical presentation is similar to acute sinusitis, with potential extension of infection into adjacent spaces:

Mucoceles most likely occur as a result of obstruction of the ostium of a sinus due to inflammation, trauma, mass lesion, etc., with resultant accumulation of mucus and eventual expansion of the sinus. Some authors (the minority) believe that they represent a mucous retention cyst that gradually enlarges, eventually filling the whole sinus 2. Chronic non-invasive fungal sinusitis has also been associated with the formation of mucocoeles 2-3. From the point of view of radiologists, which of these hypotheses is correct is immaterial.

The content of the mucocele is variable, and this impacts on the imaging appearances (see below). Most simple mucocoeles are formed by clear thick mucous. If the mucocoele has been infected (pyocoele) then the content is similar to pus.


The frontal sinus is particularly prone to developing a mucocoeles, and up to two-thirds of all mucocoeles occur there. The ethmoidal sinuses are the next most common, whereas maxillary and sphenoidal sinuses are infrequently involved 2.

Subtypes (location specific)

Mucocoeles are best imaged with a combination of CT (to assess bony changes) and MRI (to assess any extension into the orbit or intracranial compartment).

Plain radiograph

Skull radiographs do not have a significant role to play in the diagnosis of mucocoeles. If obtained, they demonstrate opacification and expansion of the affected sinus.


The affected sinus is completely opacified, and the margins expanded and usually thinned. Areas of complete bony resorption may be present resulting in bony defect and extension of the 'mass' into adjacent tissues 2-3. Peripheral calcification is sometimes seen 2. Following administration of contrast only peripheral enhancement (if any) is seen.

The content of the sinus is variable, depending on the degree of hydration, ranging from near water attenuation to hyperattenuating as secretions become increasingly thick and dehydrated 3.


MRI signal intensity is very variable and depends on the proportions of water, mucus and protein 1-3:

  • T1
    • water rich content: low signal (most common)
    • protein rich content: high signal
  • T2
    • water rich content: high signal (most common)
    • protein rich content: low signal
  • T1 C+ (Gd): enhancement if present, only occurs at the periphery
  • DWI: variable

It should be noted that colonisation with fungus can lead to very low signal on both T1 and T2 weighted sequences, mimicking a normal aerated sinus 3.

In general, drainage and marsupialisation of an affected sinus are sufficient. If large bony defects are present, reconstructive surgery may be necessary (e.g. orbital floor). If drainage remains impaired, recurrence may occur.

There is often little, if any, differential, provided contrast has been administered. Differential includes:

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Article information

rID: 9640
System: Head & Neck
Section: Pathology
Synonyms or Alternate Spellings:
  • Paranasal sinus mucocele
  • Mucocele of paranasal sinuses
  • Mucocoele of paranasal sinuses
  • Paranasal sinus mucocoeles
  • Paranasal sinus mucoceles
  • Sinonasal mucocoele
  • Sinonasal mucocele
  • Sinonasal mucocoeles
  • Sinonasal mucoceles

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Cases and figures

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    Figure 1: diagram - mucocoele
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    Mucocoele : FLAIR
    Case 1: maxillary sinus
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    Ethmoidal mucocoe...
    Case 2: ethmoid sinus
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    Case 3: ethmoid and sphenoid sinuses
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    Case 4: frontal sinus
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    Case 5: ethmoid sinus
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    Case 6: frontal sinus
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    Case 7: ethmoid sinus
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    Case 8: frontal sinus with encephalocoele
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    Case 9: ethmoid mucocele
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