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Q1: What is the diagnosis and differential diagnosis?
The radiograph shows a lucent area with osteolysis of the humeral head associated with expansion of bone and thinning of cortex, soft tissue swelling, and soft tissue calcification. The differential diagnoses are hydatid disease, tuberculosis, actinomycosis, fungal osteomyelitis, chronic bacterial osteomyelitis, chondrosarcoma, malignant fibrous histiocytoma, myeloma, metastatic disease, giant cell tumour, and aneurysmal bone cyst.1 The diagnosis of bone hydatidosis is difficult and easily overlooked unless there is a strong element of suspicion. However, presence of lucent areas, thinning of cortices, expansion of bone, associated with soft tissue calcification is highly suggestive of hydatid disease or echinococcosis.2 Eosinophilia is commonly associated.3
Q 2: What are the other sites of involvement?
Hydatid disease or echinococcosis is caused by the tapeworm Echinococcus granulosus, which inhabits the small intestine of dogs, wolves, foxes, and cats.2 Ova in their excreta infect usually cattle or humans, who are not a usual intermediary host, but are a susceptible one. The larvae migrate from the intestine through the portal vein, giving rise to hydatid cysts.5 Hydatid cysts may develop in almost any part of body. The liver is the most commonly affected organ, followed by the lung, and the remainder of the body.3 Bone involvement is rare, possibly because of mechanical resistance, and accounts for only 0.5%–2.5% of human hydatidosis.3 Skeletal sites are vertebrae (30%–40%), long bones, especially lower limbs, pelvis, ribs, scapula, and rarely in calavarium and phalanges. The cysts may remain dormant in the bone for as long as 10–20 years.4
Q3: What is the treatment?
Surgical treatment combined with chemotherapy (albendazole or mebendazole) is recommended. Chemotherapy should be given for periods of up to two years after surgery. Echinococcus larvae behave in a different manner in bones compared with soft tissues with no fibrous membrane around the osseous cysts. The behaviour of osseous hydatid cysts resembles that of locally malignant lesions.3 Curettage removes only macroscopic cysts and the local recurrence rate is 70%–80%.3,4 The only promising strategy for bone manifestations of hydatid disease is the combination of radical surgery and antihelminthic drugs over a period of up to two years.3,4
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