Pedal abscesses in patients suspected of having pedal osteomyelitis: analysis with MR imaging.

Purpose: To document the expected frequency, location, and size of pedal abscesses in patients with advanced foot infection.

Materials And Methods: Images obtained at contrast material-enhanced magnetic resonance (MR) imaging (at 1.5 T) of 161 feet of 51 women and 107 men (mean age, 58.5 years; 82.3% had diabetes) who underwent bone biopsy after MR imaging for possible osteomyelitis were reviewed by two musculoskeletal radiologists working together. Presence, size, and location of abscesses and presence of adjacent skin ulceration were noted. MR imaging criteria for abscess were the following: presence of fluid collection with isointense or hypointense signal on T1-weighted images, fluid-equivalent signal intensity on T2-weighted images, and peripheral rim enhancement. All patients' charts were reviewed for clinical and surgical information.

Results: Thirty-two fluid collections compatible with abscesses were found in 29 (18.4%) of the 158 patients; 26 (90%) of these patients had diabetes (P =.38). Abscess size varied from 1 x 0.5 x 0.4 cm to 3.8 x 3.4 x 2.2 cm (mean = 2.6 x 1.5 x 0.9 cm). Abscesses were located in the forefoot (n = 15), hindfoot (n = 7), toes (n = 3), midfoot (n = 4), or in multiple locations (n = 3). Thirty-one abscesses (97%) occurred near a skin ulcer (distance range, 0-9.1 cm; mean, 1.4 cm). Abscesses were significantly more frequent in patients with osteomyelitis (n = 28, 97%) (P <.001) and in feet that had been treated surgically (n = 16, 33%) (P <.002).

Conclusion: MR imaging revealed abscesses, predominantly in the forefoot, in 18% of patients suspected of having pedal osteomyelitis. Abscesses are significantly more frequent in patients with osteomyelitis and in feet that have been treated surgically.