Conventional and diffusion-weighted MRI of extrahepatic hydatid cysts

To evaluate the value of conventional and diffusion-weighted (DW) magnetic resonance imaging (MRI) in the diagnosis of extrahepatic hydatid cysts.

Forty-one extrahepatic hydatid cysts (12 renal, 6 pulmonary, 5 peritoneal, 4 bone, 3 soft tissue, 3 pancreatic, 2 splenic, 2 retroperitoneal, 1 adrenal, 1 scrotal, 1 diaphragmatic, and 1 cardiac) were included in this retrospective study. After a series of routine conventional MRI, DW imaging was performed using a breath-hold, single-shot, echo-planar, spin echo sequence with three b factors (0, 500 and 1,000 s/mm(2)), and apparent diffusion coefficient (ADC) maps were created. On DW trace images, signal intensity of the cysts was visually compared to the signal intensity of the muscle with the use of a 3-point scale: 0, isointense; 1, moderately hyperintense; 2, significantly hyperintense. For quantitative evaluation, signal intensity ratio and ADC of the cystic lesions were calculated.

On conventional MR images, all but 3 patients had concomitant liver involvement. Three of them were disseminated. On DW trace images (b = 1,000 s/mm(2)), most hydatid cysts (86%) were hyperintense, while five hydatid cysts (14%) were isointense. Quantitatively, the mean ADC of the hydatid cysts was 2.8 x 10(-3) +/- 0.5 mm(2)/s.

DW imaging may help in the differential diagnosis of extrahepatic hydatid cysts.