Hydatid cyst is a parasitic infection caused by Echinococcus granulosus and Echinococcus multilocularis. Liver and lung are most commonly affected organs, but any part of body can be affected.

Primary hydatid disease of muscle accounts for <1% - <4% of the reported hydatid case.(1,2) It may be postulated that the low prevalence of this form of disease is potentially due to the physical barrier to hematogenous dissemination of cyst created by hepatic sinusoids and pulmonary capillaries. In addition, the growth of the cyst within a muscle is difficult because of contractility of muscle and presence of lactic acid.(3) The most common muscle sites include neck, pelvis, thigh and paravertebral musculature. This could be explained by increased vascularity and decreased activity of these muscles.

The Gharbi ultrasound classification consist of five stages(4):

Stage 1: homogenously hypoechoic cystic thin walled lesion

Stage 2: septated cystic lesion

Stage 3: cystic lesion with daughter lesions

Stage 4: pseudo-tumor lesion

Stage 5: calcified or partially calcified lesion ( inactive cyst )

In this case cyst was included in Stage 3.

Hydatid disease should be considered in differential diagnosis of cystic lesions of muscle because routine diagnostic procedures may not always be helpful.

The treatment of hydatid disease is excision of the intact cyst with surrounding tissue with adjunctive chemotherapy by albendazole.(1)

In this particular case, the muscular hydatid cyst was removed surgically.