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Musculoskeletal » Superficial
Hydatid Cyst of the Groin and Thigh
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Presentation A 60-year old male patient presented with a large non-tender palpable mass located in the groin and the anterior compartment of his right thigh. An ultrasound of the thigh and of the abdomen was performed.
Caption: Sagittal section of the anterior compartment of the right thigh
Description: A large multiloculated cyst (13/11.4/10.8 cm), situated posterior to the sartorius muscle.
Caption: Transverse section of the anterior compartment of the right thigh.
Description: The typical aspect of daughter cysts within the cyst.
Caption: Sagittal section of the liver
Description: A well-defined, partially calcified inhomogenous mass, measuring 7/7.5 cm, is seen in the right lobe of the liver
Differential Diagnosis The differential diagnosis of soft tissue cystic masses should include synovial cyst,  abscess, chronic hematoma, as well as necrotic soft tissue tumors and hydatid cysts.
Final Diagnosis Hydatid cyst of the groin and thigh
Discussion Hydatid cysts occur most commonly in the liver (75 % of cases) and lung (15-24%), but any part of the body can be affected. Other abdominal organs may be involved in approximately 4% of cases, while soft tissue and bone are affected in only 1-2.4% of cases. [1, 2]
Primary hydatid disease of the muscle is very rare; generally, hydatid cysts are secondary to a hepatic or pulmonary lesion which leads to hematogeneous spread of the parasites. It is also possible for a retroperitoneal cyst to spread toward the lower extremity, much like a cold abscess of the psoas muscle. [2] The most common musculoskeletal locations are the neck, the trunk and the root of the extremities, probably because of their rich vascularization. [2, 3] It is uncommon for cysts to grow to very large sizes in the muscle, because of the high concentration of lactic acid and the contractility of the muscle. [2] However, in this particular case the cyst reached an impressive size – 13 cm in diameter. 
Ultrasound may identify the cyst and it may also include it into one of five types, according to Gharbi. [4] In this case, the cyst in the thigh was included in type III: cyst with daughter cysts and matrix, whereas the cyst in the liver was considered type V: calcified cyst. 
Sometimes the sonographic differential diagnosis can be difficult, especially when the  mass does not present as a typical cystic lesion with daughter cysts. In such cases, MRI has proven helpful, as it identifies a peripheral hypointense rim which has been described as specific for hydatid cysts [5], but which is not always present. [3]
The treatment of hydatid disease may be surgical or interventional. In this particular case, the muscular cyst was removed surgically; no intervention on the hepatic cyst was considered necessary, because its ultrasound aspect suggested calcification and inactivity.
This case was considered interesting since, according to a search that we conducted, there are less than forty cases of muscular hydatid cyst of the extremities reported in literature.
Case References
  1. Polat P et al, Hydatid disease from head to toe, RadioGraphics 2003; 23: 475-494.
  2. Engin G, Acunas B, Rozanes I, Acunas G, Hydatid disease with unusual localization, Eur Radiol 2000; 10:1904-1912.
  3. Garcia-Diez AI et al, MRI evaluation of soft tissue hydatid disease, Eur Radiol 2000; 10:462-466.
  4. Gharbi H, Hassine W, Brauner M, Dupuch K, Ultrasound examination of the hydatic liver, Radiology 1981; 139:459-463.
  5. Memis A, Arkun R, Bilgen I, Ustun E, Primary soft tissue hydatid disease: report of two cases with MRI characteristics, Eur Radiol 1999; 9:1101-1103
Follow Up The surgical intervention confirmed the ultrasound diagnosis: the cystic lesion of the right thigh was a hydatid cyst.
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