Retroperitoneal hydatid cyst

Case contributed by Ammar Haouimi
Diagnosis almost certain


Painless swelling of the left flank and iliac fossa.

Patient Data

Age: 55 years
Gender: Male

Large well-defined retroperitoneal multivesicular cystic mass arising from the left psoas major muscle composed of numerous cysts of variable sizes and intracystic solid matrix with an area of wall calcification. No enhancement of the cystic wall or the solid matrix on postcontrast images. A mass effect with upwards displacement on the left kidney and adjacent digestive structures as well as on the aorta and IVC which are displaced to the right. 

Small simple renal cysts are noted.

A small cyst with an imperceptible wall is noted in segment 5 of the liver suggestive of a simple cyst (confirmed by ultrasound, not shown).

Both lungs were clear on chest CT (not shown).

Case Discussion

CT features are most consistent with a large retroperitoneal hydatid cyst arising from the psoas major muscle.

Retroperitoneal hydatid infection is usually secondary to intraperitoneal infection (mainly hepatic). Isolated retroperitoneal location is rare.

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