Ankle and Foot 47 - Department of Radiology - University of ...

47 Ankle and Foot 2309 47
Figure 47-113. Evolution of involucrum in
chronic osteomyelitis in a patient with diabetes.
A, Anteroposterior radiograph reveals a somewhat
lamellated periosteal reaction around the diaphysis of
the fifth metatarsal. B, Six weeks later, the periosteal
reaction is thicker and more mature. C, Eleven weeks
later, the periosteal reaction has developed the thick,
irregular appearance of an involucrum. The
underlying metatarsal has become a dead and
sclerotic sequestrum.
A B C
Figure 47-114. Early neuropathic changes in a 66-
year-old with a long history of diabetes. Oblique axial
T1-weighted (A) and T2-weighted fat-suppressed (B)
images show marrow edema throughout the midfoot
bones.
A
B
rules out the diagnosis of osteomyelitis. However, the
converse is not true. Although the presence of bone
marrow edema may be due to infection, the edema may
represent a sterile stress response owing to the altered
biomechanics of the patient walking on a neuropathic
foot that has not yet collapsed. Indeed, marrow edema
diffusely involving several of the tarsal bones can indicate
neuropathic precollapse (Fig. 47-114), and such patients
need to be treated with a prolonged period of non–weight
bearing.
The diagnosis of osteomyelitis can be presumed when
MRI shows not only marrow edema but also abscess in the
adjacent soft tissues (Fig. 47-115) or a sinus tract communicating
from the infected bone to the skin. 1 IVGd-based
contrast is extremely helpful in diagnosing the abscess,
which exhibits thick, irregular enhancement peripherally
but not centrally (see Fig. 47-115H and K).
• Brodie’s Abscess
Brodie’s* abscess is a chronic intraosseous abscess resulting
from incomplete resolution of acute osteomyelitis and isolation
of the infection by surrounding bone. These abscess
pockets are typically found in the metaphyses of skeletally
immature children, and the usual pathogen is Staphylococcus
aureus. However, the organisms tend to be of low virulence,
*Sir Benjamin Collins Brodie (1783-1862) was an English physiologist and
surgeon who pioneered research into bone and joint disease. His most important
work is widely acknowledged to be the 1818 treatise Pathological and Surgical
Observations on the Diseases of the Joints, in which he attempts to trace the
beginnings of disease in the different tissues that form a joint and to give an exact
value to the symptom of pain as evidence of organic disease. This volume led to
the adoption by surgeons of more conservative measures in the treatment of diseases
of the joints, with consequent reduction in the number of amputations and
the saving of many limbs and lives.
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