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Imaging Diagnosis

When there is elephantiasis, the gross soft tissue deformity of the upper and lower limbs is easily appreciated on plain films (and clinically!). The long bones may show cortical thickening with a wavy contour due to periosteal new bone formation (Fig. 26.10). Although this may be simply a reaction to the lymphedema and venous obstruction, osteomyelitis must also be considered when the periosteal reaction is unilateral or focal; superimposed soft tissue infection is not uncommon in the late stage of elephantiasis. The joints remain normal unless there is a concurrent filarial synovitis. Chronic lymphatic obstruction and venous thrombosis may lead to tissue ischemia and calcification. Focal disuse osteoporosis may occur in feet, because people with elephantiasis perforce may be quite sedentary.

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Fig. 26.10A-D. The bone reaction under filarial elephantiasis. A, B Periosteal new bone formation has resulted in a thickened cortex along the tibia and fibula. C, D A Samoan patient with more severe periosteal reaction underlying large soft tissue masses. These bone changes do not indicate bone infection.

Lymphatic filariasis is the commonest form of filarial disease encountered by the radiologist. As such, most of the imaging literature pertains to infection with Wuchereria and Brugia spp. Adult and larval stages of W. bancrofti and Brugia spp. are not visible in the soft tissues on plain films unless calcified; microscopic calcification is common but is not seen on imaging. Macroscopic calcification is less common and is infrequently seen by radiologists: when visible, there are no features which allow positive differentiation of any specific worm. The calcification may be thread-like or punctate; it is often faint and is rarely vermiform. It does not have the diffuse pattern of cysticercosis, from which it is easily distinguished. Such calcification is seen on plain films, particularly of the limbs, and on mammograms, in which there may be a cluster of microcalcifications which must be distinguished from other benign or malignant processes. Calcification of filarial infection has been described in an extremity. Faint filamentous calcification can also be seen in extremity and mammography films in patients with onchocerciasis and with loiasis (see later). All filarial calcifications may be recognized on computed tomography (CT). Any superficial or pulmonary nodule containing adult worms may calcify spontaneously or after chemotherapy and, if in a favorable location (i.e., not obscured by bowel contents or bone), will be seen within an area of soft tissue thickening on ultrasonography (Fig. 26.26). Patients presenting with chyluria or hematuria will require intravenous urography. In the absence of renal colic, ureteric pressure should be applied and there may then be mild to moderate backflow of contrast medium into dilated renal lymphatics. Retrograde pyelography may show reflux that can extend as far as the major para-aortic lymph nodes and lymphatic vessels. Diffuse renal enlargement may be seen when there is severe lymphatic obstruction.

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