Teaching Case

A 91-year-old woman admitted to the emergency department with shivers, general malaise and suspicion of urinary tract infection. Patient associated also a soft, painful mass in right inguinal region. Many abdominal scars from previous surgeries were seen at the physical exploration as a result of previous cyst removals dated 20 years ago (retroperitoneal hydatidosis). A blood test revealed leukocytosis with neutrophilia, and the urine test showed pathological urine sediment with no pathologic cells.

Initial imaging with US was done and after that, a contrast-enhanced abdominal CT was performed.  In the right pelvis, we can see a retroperitoneal multiloculated lesion with soft-tissue involvement (Fig. 1) that extends from the right iliac bone. In the posterior abdominal wall, we see another multiloculated lesion that extends from the right iliac bone to the subcutaneous space. Both lesions have multiple homogenous hypodense thin wall cysts (Fig. 1). We can appreciate that the lesion has produced multiloculated bone remodulation with no periosteal reaction (Figs. 2 and 3).  With these imaging findings and the clinical history of the patient, the diagnosis of active hydatidosis was established. Due to the age of the patient, the treatment was non-surgical with echinococcus targeted antibiotherapy. 

Hydatidosis or echinococcosis is a cyclozoonosis caused by tapeworm Echinococcus granulosus larvae (1). Humans are accidental intermediary hosts, infected by direct contact with other infected animals (sheep, dogs, goats, cows) or indirectly, mainly due to ingestion of contaminated water or vegetables.

Once the intake of the larvae is produced, because of duodenum digestion the scolex are liberated into the intestinal tract. Those scolexes go through the intestinal wall reaching the venous and lymphatic system (1). The liver is the first line of defence and the most involved organ due to the fact that here most of them are eliminated by the immune system. Due to haematogenous spread, the scolex can reach almost every anatomic structure.

Hydatidosis diagnosis is based on cyst identification with imaging techniques and detection of specific serum antibodies, with tests like ELISA (high sensibility) and immunoelectrophoresis (high specificity) (2). It is important to keep in mind that depending on the cyst stage, it could be false negative, and we cannot dismiss the possibility of infection.

The “WHO-Informal Working Group on Echinococcosis” (WHO-IWGE) OMS 2003 radiology classification (3) is based on the morphology of the cyst seen by ultrasonography, it divides them in three categories: active, in degeneration and inactive. It is a simple classification that expects to unify the diagnosis (including by CT or MRI) (4) and simplify the treatment of hydatidosis,

Bone hydatid disease is a very rare clinical and radiological diagnosis (0,5 - 2% of cases) (5). Normally affects the spine, pelvis, femur or tibia. Bone cysts adopt irregular and ramified forms because they expand through low-resistance areas. Commonly cysts have a thinner wall, and in the bone is seen as a lytic, well defined lesion, with no periosteal reaction, typically multiloculated and expansive (6). As time goes by, bone cortical thinning is produced so much that it could even break and extend into contiguous soft tissues. If this happens, it can appear soft tissue calcifications. Pathological fractures are relatively common. The best imaging technique to evaluate the bone damage is CT.

Surgical excision (pericystectomy) is the treatment of choice in bone hydatid disease. To reduce cyst dimensions and to limit the infectious process it is preferred to administer Albendazol associated with chemoprophylaxis preoperatively (6). In inoperable cases the treatment can be pharmacological or percutaneous with PAIR technique (puncture, aspiration, injection and reaspiration) (3).

An early diagnosis of bone hydatid disease it is essential, considering that the advanced forms are hard to treat (even clinical or surgically) (7).

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