Paranasal sinus mycetoma

Paranasal sinuses mycetoma mycetomas, or fungus balls,are indolent and non-invasive fungal colonisation of the paranasal sinuses.  

Pathology

Pathogenesis is thought to be a cascade of processes from insufficient mucociliary clearance leading to sinus colonisation and chronic inflammatory response. The patient may only have a mild symptom or be asymptomatic. 

Radiographic features

CT

Commonly only a single sinus is affected by the predilection for the maxillary sinus followed by the sphenoid sinus. The frontal and ethmoid are less often affected. A clue to the diagnosis includes soft tissue density within the sinus with/without foci of calcific deposit. Postobstructive change may be observed if the mycetoma obstructs the sinus drainage pathway leading to partial or complete sinus opacification ². 

Evidence of chronic inflammation with sclerosis and thickening of the wall of the paranasal sinuses. Careful evaluation of the sinus cavity is prudent to exclude bone erosion that is not a feature of mycetoma / chronic fungal sinusitis rather a feature of acute invasive fungal sinusitis ².

MRI

MRI signal characteristics of mycetomas reflect the internal content of the mycelia, vegetative part of a fungus consisting of a conglomerate of hyphae. This contains primarily carbohydrates with some glycoproteins, macromolecular proteins, and iron and manganese.

Signal characteristics

• T1: low signal
• T2: low signal. The presences of paramagnetic elements further shorten the relaxation times, and this can be a highlight on the susceptibility weighted sequence ⁵
• T1 C+ (Gd): chronic inflammatory change of the sinus mucosa may enhance

Differential diagnosis

• allergic fungal sinusitis
• chronic invasive fungal sinusitis
  • bone erosion
  • soft tissue invasion
  • immunocompromised patients 
• paranasal sinus mucocele
• sinonasal inverted papilloma