MRI of eosinophilic granuloma.

The imaging studies of nine histologically proven eosinophilic granulomas were reviewed. Radiographs and MRI studies were performed on all patients, with eight patients being examined by bone scintigraphy and six by CT. Matrix calcification, not evident on radiography, was demonstrated in two cases by CT. MRI proved superior to both the radiographs and CT in defining the medullary extent of the lesion and the surrounding soft tissue changes. In eight of nine cases, on STIR sequences, an endosteal rim of low signal intensity surrounding the main lesion was present and may be an early feature of healing. The degree of peritumoral oedema accompanying eosinophilic granuloma was less extensive than that seen in either Ewing's sarcoma or osteomyelitis. The presence of both a low signal endosteal rim and limited peritumoural oedema on STIR sequences may be a useful indicator to the diagnosis of underlying eosinophilic granuloma.