Keywords: Echinococcosis/CO, Echinococcosis/SU, Echinococcus/PS, Echinococcus/CL, Muskuloskeletal System, Femur/RA, Abdomen/US, Sclerosis, Osteitis, Multiple Hypodense Lesions, Human, Male, Adult, Case Report,
|How to cite this article:|
Patel N G, Sainani N I. Primary musculoskeletal hydatid disease. Indian J Radiol Imaging 2002;12:545-6
| Introduction|| |
Hydatid disease is caused by the larval form of two small tapeworms, Echinococcus granulosus, the common unilocular form and Echinococcus multilocularis, the graver, alveolar form . Hydatid disease of the skeletal system is a rare parasite infection (1-2 percent of all cases)  presumed to occur when a blood-borne scolex passes the filters of the liver and the lung, enters the arterial tree and is carried to a bone . Approximately 60 percent of cases are found in the spine, pelvis and hip joint; 28 percent in the long bones (femur, tibia, humerus); and 8 percent in the ribs and the scapula. Isolated cases have been reported in calvarium and phalanx. Involvement to the muscles occurs in 3 percent of the cases . We report a case of primary musculoskeletal hydatid disease involving the femur and adjacent muscles with imaging findings on plain radiographs, US and CT. Confirmation was done by surgical exploration.
| Case Report|| |
A twenty-six year old man presented with complaints of pain and swelling in his left thigh. The pain, intermittent for approximately one year, had increased during the past two months. He also stated that recently he had been unable to bear weight on the involved limb without eliciting marked pain in the thigh. Examination of the affected limb revealed a swelling in the lower thigh with tenderness.
Plain radiograph of the left femur showed multiple lytic lesions in the distal diametaphyseal region. A large lytic lesion was seen in the mid-shaft region expanding the cortex anteromedially. Intervening segments of sclerotic bone were seen and the cortex in the involved region was thickened [Figure - 1]. The lesion did not extend into the epiphysis or the knee joint. Displacement of the adjacent fat planes and swelling of the adjacent soft tissues were noted. Skeletal survey did not reveal any other similar lesion elsewhere in the skeletal system. The Lung fields were normal. US examination of the left thigh revealed multiple well defined anechoic lesions in the region of the soft tissue swelling [Figure - 2]. US of the abdomen was normal. CT of the affected limb showed expansion of the medullary cavity with multiple hypodense lesions having enhancing walls, intermittent areas of cortical thinning, expansion and sclerosis were noted [Figure - 3]. Multiple hypodense lesions of variable sizes with wall enhancement were noted in the adjacent muscles [Figure - 4].
An exploratory operation of the left thigh was performed. The cortex of the femur was removed which uncovered multiple cystic areas. The material from the cavity consisted of small, round whitish circumscribed cystic masses ranging in size from 0.5-1.5 cms in diameter. Similar cysts were removed from the adjacent muscles. The appearance of the cystic bodies suggested the diagnosis of hydatid disease and was subsequently confirmed on histopathology
| Discussion|| |
Hydatid disease in bones occurs most in commonly vascularised areas. The vertebrae, long bones, ileum, skull and ribs are affected in descending order . In the bone, because of the resistance of the tissue, the parasite is unable to follow its usual mode of development . The development of the radiographic findings comprises three stages . The first stage comprises of microvesicular infiltration, in which the embryos are deposited in the bone and cause destruction by mechanical pressure and local necrosis by impairment of the blood supply ,. Microvesicles are produced by exogenous budding along the line of least resistance in an irregular branching fashion, producing grand daughter vesicles that invade bony tissue and eventually replaces the medullary tissue. As the cysts enlarge, cyst like spaces develop that are lined by thin trabeculae and give a multilocular appearance to it resembling a "bunch of grapes" ,,. The early bone lesion is represented by an ill-defined thin walled area of radiolucency in the epiphyseal end that has a multilocular appearance. There is no sharp demarcation between the lesion and the surrounding normal bone, no periosteal reaction or proliferation of new bone. Later, well defined round or oval cystic areas become apparent. Extension and coalescence of the cysts result in an overall loss of bone structure, resembling a large communicating cyst with a lattice type of trabecular pattern. Pathological fractures occur during the first stage. In the second stage, a secondary infection is engrafted on the hydatid process producing an inflammatory osteitis, which results in thickening of trabecular bone, bony condensation, cortical bone loss and hyperostosis. Our patient was seen in this stage. The third stage involves the formation of an ossifluent abscess, which occurs after penetration of the cortex and protrusion of the exuberant growth into the adjacent soft tissues which appear radiologically as a smooth rounded mass in the adjacent soft tissues ,,. The cysts that develop in the soft tissue are spherical, may reach several centimeters in diameter and may subsequently undergo calcification . US and CT are usually nonspecific however, loculated cystic lesions in the bone and soft tissues are seen and it helps to determine the precise site and extend of the lesion.
In the long bones, the early bone lesions, consisting of ill-defined multicystic areas of radiolucency must be differentiated from fibrous dysplasia, neurofibromatosis, solitary bone cyst, aneurysmal bone cyst, plasmacytoma, cartilaginous neoplasma (enchondroma, chondrosarcoma, chondromyxoid fibroma) and giant cell tumour . Later in the course of the disease, when secondary infection has set in, the radiologic features resemble those of osteomyelitis.
MR is considered to be the best imaging modality for the evaluation of musculoskeletal hydatid disease. MR shows the exact site, extent and may help in differential diagnosis.
| References|| |
|1.||Wlner D. Radiology of bone tumours and allied disorders, 4th edition. WBSaunders, 1982;1144-1179 |
|2.||Beggs I. The radiology of hydatid disease. American Journal of Radiology, 1985;145:639-648. [PUBMED] |
|3.||Resnick D, Niwayana G. Diagnosis of bone and joint disorders, 2nd edition. WBSaunders, 1988;2738-2739. |
|4.||Edeiken J, Dalinka M, Karasick D. Roentgen diagnosis of disease of bone, 4th edition. Williams and Wilkins, 1 989; 1053-1054. |
N G Patel
Department of Radiology, B.J. Medical College, Civil Hospital Campus, Ahmedabad, Asarwa-380016, Gujarat, India
Source of Support: None, Conflict of Interest: None
[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4]