Nonenhancing tissue on MR imaging of pedal infection: characterization of necrotic tissue and associated limitations for diagnosis of osteomyelitis and abscess.
OBJECTIVE
We studied the frequency, location, extent, and signal characteristics of nonenhancing tissue in pedal infections and correlated those areas with surgical and histologic findings.


METHODS
One hundred ten contrast-enhanced 1.5-T MR imaging foot examinations in 102 patients (28 women, 74 men; mean age, 59 years), 82% of whom had diabetes mellitus, were reviewed by two musculoskeletal radiologists for the presence of areas without recognizable enhancement. The number, size, location, signal characteristics, and enhancement ratio of nonenhancing regions were noted. MR imaging findings were compared with surgical and histology reports.


RESULTS
Nonenhancing regions were found in 27 feet (24.5%, 96.3% in diabetic patients, p = 0.032) at the forefoot (n = 16), toes (n = 8), and heel (n = 3). The mean size of the nonenhancing regions was 4.1 x 2.7 x 1.4 cm. Signal characteristics on T1-weighted images were isointense to muscle (n = 21, 77.8%), hypointense to muscle (n = 3, 11.1%), heterogeneous (n = 2, 7.4%), and isointense to fat (n = 1, 3.7%). On T2-weighted images, the signal was hyperintense to muscle (n = 12, 44.4%), heterogeneous to muscle (n = 9, 33.3%), equal to fluid (n = 3, 11.1%), and hypointense to muscle (n = 3, 11.1%). The mean signal increase after contrast administration was 3.57% for observer 1 and 2.68% for observer 2. Necrotic tissue was surgically confirmed in the nonenhancing areas in 26 feet (96.3%). Five abscesses and three cases of osteomyelitis were misdiagnosed on MR images because of lack of enhancement.


CONCLUSIONS
Nonenhancing areas are seen in one fourth of pedal infections, occur almost exclusively in diabetic patients, and represent necrotic tissue. Only contrast-enhanced images allow reliable recognition of these regions. Lack of enhancement in these areas can mask the presence of abscess and osteomyelitis.
Ledermann
Hans Peter
HP
Department of Radiology, Thomas Jefferson University Hospital, 111 S. 11th St., Rm. 3390 Gibbon, Philadelphia, PA 19107, USA.
Schweitzer
Mark E
ME
Morrison
William B
WB
D000038:Abscess / Q000175:diagnosis*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016477:Artifacts; D017719:Diabetic Foot / Q000175:diagnosis*; D003937:Diagnosis, Differential; D005260:Female; D005534:Foot Diseases / Q000175:diagnosis*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009336:Necrosis; D010019:Osteomyelitis / Q000175:diagnosis*