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Imaging Diagnosis

The radiologist may not only make the diagnosis of tropical ulcer, but also may provide important information concerning the progress of the ulcer and possible development of malignancy. The roentgenological findings will be considered in the same sequence as the clinical findings.

The vast majority of tropical ulcers develop in the lower leg, overlying the tibia or the fibula. For the first 5 days, until a pustule discharges, there are no significant radiological findings. Once the ulcer has developed there is usually marked soft tissue thickening, visible in profile radiographically or with ultrasonography. As the ulcer spreads, the earliest radiological finding in bone is a periosteal reaction which is localized immediately beneath the ulcer (Fig. 36.3). In most cases this begins as a minimal layered, fusiform periosteal reaction (Fig. 36.3 A), but occasionally "sunray" spicules develop (Fig. 36.3B). The periosteal reaction then blends with the original cortex to produce a thickened sclerotic layer which may be as much as 1-inch (2.5 cm) in thickness (Fig. 36.3 C-I). At this stage it is called an "ivory osteoma" and the multilayered periosteal reaction or spicules will no longer be visible. This ivory periosteal reaction can eventually involve the whole circumference of the bone and extend above and below the site of the ulcer. As it does so, it often becomes wavy and irregular, varying in width and in outline.

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Fig. 36.3A-D. The development of the periosteal and bone reaction under a tropical ulcer. (A) Fusiform periosteal reaction layered around the midshaft of the tibia. (B) A similar somewhat more exuberant reaction with some "sunray" spicules at the lower end of the fibula. (C) The periosteal reaction around this tibia has blended with the original cortex to produce a localized area of thickening. The patient was a 13-year-old from Guinea, West Africa (Courtesy of Dr. W.M. Thomas). (D) A thickened sclerotic reaction on the middle of the tibia.

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Fig. 36.3E-G. (E) As this progresses there is resorption from the medullary side, leaving a bulbous expansion with some cortical thickening. (F) The lower part of the cortex over this expanded lower fibula is almost normal. (G) Both the tibia and the fibula are expanded. The cortical thickening on the front of the tibia is wavy; the fibula is quite smooth.

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Fig. 36.3H-I. (H)"A blister" has formed by a combination of periosteal reaction and cortical thickening in the upper third of the tibia. There is quite marked cortical thickening in the lower third of the tibia, below the ulcer. (I) A large "ivory osteoma" has developed below a tropical ulcer. This will have to be removed surgically before complete healing of the soft tissues can be expected.

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