[Nuclear magnetic resonance tomography after fatty tissue obliteration of the frontal sinus].

Background: The osteoplastic flap procedure with fat obliteration has been hailed as the gold standard of definitive frontal sinus procedures for chronic inflammatory disease. The value of magnetic resonance imaging (MRI) in postoperative follow-up has not yet been sufficiently examined.

Methods: All postoperative MRI scans performed in patients undergoing surgery between January 1, 1986, and December 31, 1996 were evaluated. The outcome parameters were time-dependent changes in the distribution of fatty or connective tissue and development of necroses or oil cysts, as well as recurrences, inflammatory complications, or mucoceles.

Results: Sixty-eight operations were performed in the specified period and a total of 73 postoperative MRI scans from 45 operations were available for evaluation. In 16 cases, between two and five MRI scans were available. The individual time between surgery and the last MRI scan ranged from two weeks to 130 months with an average of 30.1 months. We found four mucoceles 34, 49, 106, and 130 months, respectively. Three of the mucoceles were diagnosed on the first postoperative MRI scan. In the fourth case the mucocele had not been seen on the previous scan. The amount of adipose tissue depictable on the last scan was less than 20% in the majority of cases (58%) and more than 60% in only 18% of cases, although in the latter group the time between surgery and MRI was less than 7 months in half the cases.

Conclusions: MRI is the most valuable diagnostic tool after frontal sinus obliteration using adipose tissue. Despite the good soft tissue differentiation, the method has some limitations with regard to detection of small recurrent mucoceles and differentiation between vital adipose tissue and fat necrosis in the form of oil cysts. In these difficult cases, long-term MRI follow-up is necessary for definitive evaluation. We therefore recommend MRI 1, 2, and 5 years after osteoplastic frontal sinus surgery with obliteration.