Imaging of spinal hydatid disease

Abstract

Hydatid disease (echinococcosis) is a parasitic infection caused more frequently by Echinococcus granulosus and less frequently by E. multilocularis (E. alveolaris), the liver and lungs being the most commonly involved organs. Involvement of the spine is rare but it is clinically challenging. Thoracic vertebrae are more commonly involved, sometimes misleading to the diagnosis of Pott's disease. Patients usually present with symptoms caused by spinal cord or nerve root compression. Hydatid cysts were classified as intramedullary hydatid cysts, intradural extramedullary hydatid cysts, extradural-intraspinal hydatid cysts, hydatid cysts of the vertebrae, and paravertebral hydatid cysts. Intradural hydatid cysts are rare. The disease usually begins in the vertebral body. Extension into the spinal canal results in spinal cord and neural compression. The parasite may destroy the cortex, causing spread of hydatid cysts into the surrounding soft tissues and adjacent parts of the skeleton. After obtaining plain X-rays, both computed tomography (CT) and magnetic resonance imaging (MRI) should be used for further imaging, which are of value in preoperative planning of the surgical approach to hydatid lesions of the skeleton. On both CT and MRI, the appearance of the cystic fluid resembles that of cerebrospinal fluid. Usually no rim enhancement is evident after injection of contrast material, though there may be exceptional cases. CT is effective in demonstrating the destructive hydatid lesions in vertebrae, in determining their spread, and in establishing the presence of other hydatid cysts in adjacent soft tissues. MRI can more effectively demonstrate complications such as spinal cord and/or nerve root compression, and it is the diagnostic procedure of choice in the face of neurological deficit. On MRI of spinal hydatid disease, cyst walls are thin and regular. The presence of a markedly hypointense cyst wall on T1-weighted and T2-weighted images and the absence of wall enhancement with gadolinium are characteristic. Follow-up MRI is used postoperatively to rule out any recurrence of the cysts. Diffusion-weighted MRI can help differentiate complicated hydatidosis from other cystic lesions. In conclusion, hydatid disease should be considered in the differential diagnosis of a cystic lesion in the spine, in areas where the disease is endemic. MRI is the most efficient imaging modality in diagnosis of spinal hydatid disease and in demonstration of its complications.