Title: T1-Weighted MRI Characteristics of Pedal Osteomyelitis
Authors: Collins MS, Schaar MM, Wenger DE, Mandrekar JN
Source: American Journal Of Roentgenology 2005; 185:386-393.
PODIATRIC RELEVANCE:
Among imaging modalities utilized by podiatric surgeons, MRI studies have been shown to be useful in diagnosing pedal osteomyelitis. Although typical characteristics of osteomyelitis have been described (decreased T1 signal and increased T2 marrow signal), these findings may also be present in various pedal conditions, thus reducing MRI specificity. Some known causes of false-positive results on MRI in cases of pedal osteomyelitis include reactive marrow edema, neuropathic arthropathy, stress reaction, and altered weight bearing. Recognizing this fact, precise imaging interpretation is crucial as it may prevent surgical morbidity. This article attempts to better define the T1-weighted MRI characteristics of surgically proven pedal osteomyelitis.
METHODS:
A retrospective study of patients from the Mayo clinic with an MRI diagnosis of pedal osteomyelitis and correlating tissue diagnosis with surgical biopsy or amputation were reviewed by two experienced musculoskeletal radiologists. Time interval between the MRI examination and subsequent surgery was less than 6 weeks in all cases. The reviewers were aware of the histopathologic diagnosis at the time of their analysis. The study group consisted of 80 feet in 80 patients, 63 of whom affected by diabetes, with ages ranging from 22 to 89 years.
There were two study groups: true-positive cases (MRI originally interpreted as osteomyelitis and surgical pathology interpreted as osteomyelitis) or false-positive cases (MRI originally interpreted as osteomyelitis and surgical pathology interpreted as negative for osteomyelitis). Primary T1 imaging characteristics evaluated included T1 signal intensity of the affected bone marrow as compared with normal adjacent fatty marrow (decreased vs. normal), T1 signal intensity as compared with adjacent skeletal muscle (decreased or isointense vs. increased), the distribution of the signal abnormality (subcortical vs. medullary), and the pattern (hazy, reticulated vs. confluent). The appearance of the affected bone cortex (abnormal vs. normal) was evaluated as well. Abnormal bone cortices were further evaluated for complete disruption or intact with irregularity.
RESULTS:
Of the 80 patients in the study group, 59 were true-positive and 21 were false-positive. There was no statistical difference with regard to patient age, sex, or the presence of diabetes. All 59 true-positive cases of osteomyelitis showed decreased T1 marrow signal in a geographic medullary distribution with a confluent pattern and concordance (decreased T1 signal with confluent pattern and a matching area of increased T2 signal intensity) with T2 marrow signal abnormality. No cases of surgically confirmed osteomyelitis had primary T1 findings with subcortical distribution; hazy, reticulated pattern; or discordance (T1 marrow signal normal or hazy, reticulated pattern with increased T2 signal abnormality) with the T2-weighted images. The presence of ill-defined, decreased T1 signal within the marrow with a hazy, reticulated pattern (as opposed to a confluent pattern) was felt to be strongly suggestive of reactive marrow edema regardless of the T2-weighted or contrast-enhanced imaging findings. A subcortical (rather than medullary) distribution of the T1 signal abnormality was seen only in the false-positive group and was may be attributed to reactive marrow edema.
COMMENTS:
Foot and ankle surgeons commonly utilize and depend on MRI in diagnosing osteomyelitis due to its capability of detecting abnormalities in both bone and soft tissue. Accurate and prompt diagnosis is essential in providing appropriate care for the podiatric patient and preventing unnecessary medical and surgical management, thereby decreasing patient morbidity and mortality. A greater comprehension of the specific imaging characteristics of pedal osteomyelitis as well as those conditions that may produce false-positives, better equips the surgeon in treatment of the podiatric patient. This study, although retrospective in nature, is useful because it analyzes abnormalities and patterns specific to feet that have surgical histopathologic confirmation of osteomyelitis.
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Disclaimer:
Scientific Abstract Monthly postings are submitted by podiatric surgical residents. The ideas presented are not the opinions of the American College of Foot and Ankle Surgeons (ACFAS), nor are they presented as facts. ACFAS presents this information without any warranty of any kind, expressed or implied, and is not liable for its accuracy nor for any loss or damage caused by the user's reliance on information obtained in these areas.