Magnetic resonance imaging following fat obliteration of the frontal sinus

The paper describes the evaluation of magnetic resonance imaging (MRI) following osteoplastic flap procedure with fat obliteration. MRI scans performed in patients after surgery between 1st January 1986 and 31st December 1997 were evaluated. Outcome parameters were time-dependent changes in the distribution of adipose or connective tissue, development of necroses or oil cysts, recurrences, inflammatory complications, or mucocoeles. Eighty-six postoperative MRI scans from 51 operations were evaluated. In 19 cases between two and five MRI scans were available. Time between surgery and the last MRI scan was 24.1 months on average. We found five mucocoeles. The amount of adipose tissue depictable on the last scan was less than 20% in the majority of cases (53%) and more than 60% in only 18% of cases. Statistical tests and modelling showed a significant decrease of adipose tissue with time, with a median half-life of 15.4 months in a subgroup with at least two MRIs. MRI is at times the most valuable diagnostic tool after frontal sinus obliteration using adipose tissue. The method has some limitations with regard to detection of small (recurrences of) mucocoeles and differentiation between vital adipose tissue and fat necroses in the form of oil cysts. In difficult cases long-term MRI follow-up is necessary for definitive evaluation.