Osseous Hydatid Disease : A Rare Cause of Pathological Fracture
Osseous hydatid disease is very rare. Patients can be asymptomatic for a long period following which they will present with either a swelling or a pathological fracture or both. We present a case of a 71-year-old man with a history of a previous fall who presented with pain and swelling of the left thigh. X-ray showed an old fracture of the femur shaft with non union. The fracture was treated with an implant following which the patient developed a discharging sinus. During the second surgery for non union, curetted tissue was sent for a histopathologic examination and it was diagnosed as hydatid disease of bone. Preoperative diagnosis of osseous hydatid disease is difficult as other neoplastic and non-neoplastic diseases cannot be differentiated radiologically without a high index of suspicion. Possibility of hydatid disease has to be kept in mind while dealing with pathologic fractures especially in an endemic region.
Hydatid disease is caused by the larva of Echinococcus granulosus (EG) and may develop in almost any part of the body. The overall incidence of organ infestation is greatest in the liver (50-77%) and the lungs (8.5-45%). Involvement of the central nervous system (CNS) is 3% of all hydatid disease. Incidence of bone involvement is much lower, about 0.5-4% of the total reported cases and is mostly seen in the spine (50-60%), followed by the femur, tibia, humerus, skull and ribs.[1,2,3] Early diagnosis is uncommon and patients usually present late.
Case report :
A 71-year-old man presented with pain and swelling of the left thigh. He had a history of a fall one month prior to presentation for which he had received an alternate medicine treatment. The X-ray showed an old fracture of the shaft of the femur with non–union. Routine laboratory investigations, chest x-ray and ultrasound abdomen were all within normal limits. The fracture was treated with limb reconstruction system (LRS) following which the patient a discharging sinus. LRS removal and fracture site debridement and intra medullary nailing with bone grafting was done after two weeks. Curetted tissue was sent for histopathology which comprised of membranous tissue bits with friable haemorrhagic material. Multiple sections studied showed viable and non–viable bony trabeculae, fibrin with areas of calcification and foreign body reaction. Multiple fragments of lamellated eosinophilic membranous tissue lined by innermost germinal layer with nuclei were seen (Figure 1).
Diagnosis of hydatid disease of the bone was made. Patient was discharged with albendazole 400mg for a duration of 14 days. On follow up, he was symptomatically better without any swelling or discharging sinus.
Primary hydatid disease of the bone, due to EG, occurs when a blood borne scolex settles in bone. In bone involvement, pericyst formation does not occur, thereby allowing aggressive proliferation in an irregular branching fashion along the line of least resistance, especially the bone canal. The parasite replaces the osseous tissue between trabeculae due to slow growth of multiple vesicles. With time, the parasite reaches and destroys the cortex with subsequent spread of the disease. Slow resorption of the trabeculae, without cortical expansion, occurs as a result of pressure.
Hydatid disease was first reported in the spine by Chaussier in 1807, and thereafter it was regularly reported.[1-5] Patients usually present with pain, swelling and pathological fractures. As there is a lack of a characteristic clinical appearance and image characteristics on X-ray or computed tomography (CT), hydatid cyst is usually difficult to distinguish from tuberculosis, chronic osteomyelitis, aneurysmal bone cysts, Giant cell tumors, solitary cysts, neurofibromatosis and chondrosarcoma. To diagnose it correctly, serological assay methods are available.[2,6] However, despite all investigative measures diagnosis is usually established only at surgery or during histopathological study of these lesions.
The hydatid cyst has three layers: (1) the outer pericyst, composed of modified host cells that form a dense and fibrous protective zone (2) the middle laminated membrane which isacellular and allows the passage of nutrients and (3) the inner germinal layer, where the scolices (the larval stage of the parasite) and the laminated membranes are produced. The middle laminated membrane and the germinal layers form the true wall of the cyst, usually referred to as the endocyst, although the acellular laminated membrane is occasionally referred to as the ectocyst. Daughter vesicles (brood capsules) are small spheres that contain the protoscolices and are formed from rests of the germinal layer. Before becoming daughter cysts, these daughter vesicles are attached by a pedicle to the germinal layer of the mother cyst. At gross examination, the vesicles resemble a bunch of grapes. Daughter cysts may grow through the wall of the mother cyst, particularly in bone is ease. Cyst fluid is clear or pale yellow with a neutral pH and it contains sodium chloride, proteins, glucose, ions, lipids, and polysaccharides. The fluid is antigenic and may also contains colices and hooklets. When vesicles rupture within the cyst, the scolices pass into the cyst fluid and form a white sediment known as hydatid sand.
The present case of hydatid bone disease was not suspected preoperatively, and immunological tests such as haemagglutination and total and specific Immunoglobulin E (IgE) level measurements were not performed, although they are recommended in the literature as preoperative diagnostic parameters. Surgery is the treatment of choice for bone hydatid lesion with or without using albendazole or mebendazole. Complete excision of the cyst is required as the recurrence rate is high with incomplete removal.[2,7]
The diagnosis of primary bony hydatidosis is difficult. It may be easily overlooked and usually requires a high index of suspicion. In endemic areas such as in India, hydatid disease should be considered in the differential diagnosis of any cystic/osteolytic lesions of bones. Preoperative diagnosis is essential for correct surgical planning and prevention of recurrence, especially in a setting like ours where far-flung areas and low socio-economic status are practical problems in patient care and follow-up.
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