Background: Distinction between uncomplicated infective fasciitis and early necrotizing fasciitis can be extremely difficult without operation, yet the management and prognosis of both conditions depend greatly on early recognition and assessment of the extent of involvement.

Study Design: This was a prospective review of the utility of magnetic resonance imaging (MRI) in nine patients with suspected infective or necrotizing fasciitis treated at an academic medical center or a Veterans Administration hospital.

Results: Magnetic resonance imaging documented fascial inflammation, characterized by low intensity on T₁-weighted images and high intensity on T₂-weighted images, in all nine patients. Absence of gadolinium contrast enhancement on T₁-weighted images reliably detected fascial necrosis in all six patients who required operative debridement. Magnetic resonance imaging was extremely useful in defining the extent of fasciitis and was more accurate in predicting necrosis or pyomyositis than was myoglobinuria or elevation of serum creatine kinase or lactate dehydrogenase. Operation was avoided in two patients without evidence of necrosis on MRI. One patient without evidence of necrosis, explored because of contradictory clinical findings, was confirmed at operation to have cellulitis without necrosis.

Conclusions: Magnetic resonance imaging with gadolinium contrast accurately determines the presence of necrosis and the need for operation in patients with fasciitis of the lower extremity. Preoperative determination of the extent of involvement facilitates operative planning.