An unusual presentation of hydatid cyst within the soft tissues of the back: re-investigation of the undiagnosed lung opacity.

BACKGROUND: Echinococcosis is a zoonotic infection, affecting humans in a characteristic geographic distribution. The disease most commonly involves the liver and the lung and a soft tissue localization is very rare.
METHODS: A case of a 68-year-old man, who presented with a cystic lesion on his back, which was presumed to be a lipoma or a sebaceous cyst. Surgical excision of the lesion was performed.
RESULTS: Histopathology revealed a hydatid cyst and with further investigations, we identified the nature of a previously undiagnosed opacity in the right lung field. Although the patient previously presented with symptoms of hydatid cyst rupture (productive cough with haemoptysis), echinococcosis was not under consideration.
CONCLUSIONS: This unusual case serves to demonstrate that echinococcosis, though rare, should be considered in the differential diagnosis of cystic lesions in every anatomic location, especially when they occur in endemic areas. We overview the diagnosis and treatment of this parasitic infection.