Echinococcus is a species of the Taeniidae family, which usually lives outside of the human body. This species has a high potential for the formation of a hydatid cyst in the human body. Humans can be infected through the accidental ingestion of eggs of Echinococcus from contaminated water or food. Hydatid cysts have been recognized as an endemic disease in many parts of the world (1,2). Hydatidosis in 59-75% of cases occur in the liver, 27% in the lung, 3% in the kidney, and 1-2% in the brain. The incidence of bone involvement is about 0.5-4% of all hydatid disease in human body and isolated cysts of the bone are very uncommon. Bone involvement is mainly secondary to the liver and kidney involvement (3). There are very few reports of primary bone involvement and femoral bone involvement by hydatid cysts. In this article, similar to our previous study with educational view (4), we report a case of original hydatid cyst in the femur that caused pathological fracture.
 

Discussion

In some areas of the world, there is a higher prevalence of hydatid disease than others, as shown in Figure 3. Cystic echinococcosis involvement of the bone is an extremely rare condition even in endemic areas including the Middle East, Mediterranean countries, South America, North Africa, and Australia.  Hydatid cysts often affect the lung and liver but rarely involve other organs such as the bone, and more than one organ has been reported to be involved in 20%-30% of cases.  A very small percentage of the bone cysts may grow in the femur (2). Table 1 shows the cases reported in the literature.
Many bone hydatidoses often remain asymptomatic, even in advanced age, and are diagnosed when the bones are fractured by a low-energy trauma or by pressure on adjacent components such as nerves or vessels (5). Hydatid bone disease is usually difficult to be distinguished from chronic tuberculosis osteomyelitis, osteomyelitis, aneurysmal bone cysts (benign bone tumor with destruction), giant‐cell tumors, solitary cysts, neurofibromatosis, a fibrocystic disease without direct tissue observation through surgery or histopathology. For this reason, rapid detection of hydatid cysts is very unlikely and the initial diagnosis is generally based on X-Ray graphs. Multiple clear cysts with bone expansions are shown in the X-ray images. Occasionally, bone sclerosis that produces a honeycomb-like appearance is seen. A plain X-ray image cannot make a definitive diagnosis. The addition of a CT-Scan and MRI may help to identify the area of involvement or the severity of the case (6).
Eosinophilia occurs in only 25% of cases and eosinophilia was not observed in our patient.  Fine-needle aspiration (FNA) is not recommended because of the risk of cyst spreading elsewhere (adjacent sites) or septic shock (7). The reason for the late diagnosis of hydatid cysts in the bone is the absence of symptoms due to a slight increase in the size of the cyst, in other words, as the size of the cyst increases and it grows the symptoms of the cyst appear (2). The diagnosis in our case was made when the growth of the cyst had reached such a level that it had fractured the bone by a low energy trauma.
 The presence of a large number of dogs in suitable climatic and environmental conditions creates the ground for egg survival. As mentioned, our case also reported contact with several dogs in his history. The treatment of these patients differs from those of traumatic fractures of the bone. Extensive resection should be performed in the affected area (2). Despite the risk of rise of protoscoleces during surgery, it can still be considered as the best therapy modality in these patients. Several therapeutic options may be recommended as the best treatment. One of these suggestions is the use of mechanical curettage in the involved area, the use of electric milling machines, hypertonic saline, povidone-iodine, formalin, or 0.5% silver nitrate to sterilize the involvement area. Finally, the use of autograft bone is sometimes suggested in the area (8).
Monge-Maillo et al., (2017), proposed the use of bone cement or polymethylmethacrylate (PMMA) to cover defective sites in 2017 (9). The use of intramedullary nails is another suggestion that was first proposed by Booz (1972) and colleagues (10). We followed this approach in our treatment method. In the proximal femoral bone cyst textures, valuable suggestions such as the use of custom mega prosthesis have been made. Despite all efforts, recurrence occurs in some patients. If soft tissue is broadly involved, chemotherapy is administered using albendazole or mebendazole as a standard recommendation. The WHO recommends albendazole (400 mg twice a day) for a period of 28 days, which may be repeated. It also prescribes mebendazole 50 mg/kg daily for at least three months (11).

 
Figure 3. Distribution of Echinococcusgranulosus and cystic echinococcosis, worldwide, 2011
 

Table1. Case reports of femoral -bone Hydatidosis

Conclusion

It seems that the definitive treatment of femoral bone hydatid cysts is not surgical resection and intramedullary nail placement alone. In addition to resection of the cyst, the infected area should be removed extensively and the defected area, if needed, covered by cement or bone allograft. Regular chemotherapy may play a key role in post-operative treatment. Finally, it is worth noting that orthopedic surgeons should be aware of this type of pathological fracture. It can be concluded that paying attention to the long-term complications of fractures requires educational considerations during the professional performance of surgeons.

 

Acknowledgements

None.

 

Conflicts of Interest

The authors declare no conflict of interest.