DISCUSSION :
Hydatidosis is a zoonotic disease caused by the larval form of Echinococcus granulosus. Humans become accidental hosts by ingesting taenia eggs. The larvae are released in the duodenum, cross the wall, and pass through the portal system to the liver (1). Bone involvement is rare, occurring in only 0.5 to 2.5% of all hydatid cases (1), the blood-borne route is the most common, but it is also possible for primary soft tissue involvement to lead to secondary bone invasion. Spinal involvement typically occurs in the vertebral body due to portovertebral shunts. The dorsal spine is affected in 80% of cases, followed by the lumbar spine (18%) and the cervical spine (1%) (2). Hydatid cysts can cause pain, local soft tissue swelling, and pathological fractures. In our patient, the cyst compressed the rectum.
Hydatid serology is typically negative and only becomes positive during the stage of soft tissue invasion (2, 4). The radiological appearance is non-specific, initially consisting of multiple localized lacunae that gradually become confluent, creating a grape-like appearance (5).
CT scans and magnetic resonance imaging (MRI) can be used to better define bone lesions, assess extension to adjacent structures, and guide surgery. Prolonged monitoring is also enabled, but in this case the CT scan was not very conclusive.
Hydatid vesicles appear in T1 hypersignal and T2 hypersignal on MRI in their typical form (6,7,8).
The differential diagnosis should consider tuberculous spondylodiscitis, metastases, and aneurysmal cysts.
The treatment for osseous echinococcosis currently involves medical and surgical interventions. The medical treatment aims to reduce cyst size, sterilize their contents before surgery, and treat small cysts that may go unnoticed postoperatively.
The prognosis for this disease is often burdened by frequent recurrences and involvement of adjacent soft tissue, as surgical excision is often incomplete. The best treatment for this disease remains active prevention (1).