Mycetoma in chronic fungal sinusitis
Mycetoma in chronic fungal sinusitis is an indolent, non-invasive fungal colonization of the paranasal sinuses.
Pathogenesis is thought to be a cascade of processes from deficient mucociliary clearance leading to sinus colonization and chronic inflammatory response. The patient may only have a mild symptom or be asymptomatic.
Commonly only a single sinus is affected with the predilection for the maxillary sinus follow by the sphenoid sinus. The frontal and ethmoid is less often affected. A clue to the diagnosis includes soft tissue density within the sinus with/without foci of calcific deposit. Post obstructive 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 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.
Mycetoma appear as low signal intensity on both T1WI and T2WI with T2WI being more conspicuous. The presences of paramagnetic elements further shorten the relaxation times, and this can be a highlight on the susceptibility weighted sequence 5.
Chronic inflammatory change of the sinus mucosa may enhance on post contrast T1WI.