| Abstract|| |
Hydatid disease has a worldwide distribution and causes health problems in endemic countries. The prevalence of primary muscular hydatid disease is reported to be only 0.5% because muscle is an unfavorable site for infestation as a result of its high levels of lactic acid. Primary intramuscular hydatid cyst presents a diagnostic problem not only because of the unusual location and low prevalence, but also because complicated cysts may imitate solid or complex lesions.
We report an unusual case of primary hydatidosis of the calf muscles, in which a wide excision was performed without causing any damage to the cyst wall. Injudicious approach in the management of these rare presentations may be the root cause of severe anaphylactic shock and systemic dissemination. Intramuscular hydatid cysts grow gradually and may mimic a soft tissue tumor; thus, the diagnosis of soft-tissue hydatid cysts needs a high index of suspicion.
Keywords: Echinococcus granulosus, hydatid cyst, intramuscular
|How to cite this article:|
Sinhasan SP, Palachandra A. Primary intramuscular hydatid cyst: A rare case report. Ann Trop Med Public Health 2012;5:546-8
| Introduction|| |
Hydatid disease has a worldwide distribution and causes health problems in endemic countries. The prevalence of primary muscular hydatid disease is reported to be less than 0.5% in endemic populations because muscle is an unfavorable site for infestation as a result of its high levels of lactic acid.  Primary intramuscular hydatid cyst presents a diagnostic problem not only because of the unusual location and low prevalence, but also because complicated cysts may imitate solid or complex lesions.  The differential diagnosis in these cases must include malignant soft-tissue tumors such as myxoid liposarcoma, soft tissue abscesses, and chronic hematoma. 
In recent years, human hydatid disease caused by Echinococcus granulosus has been recognized as a public health problem of global dimensions.  It is found in all sheep-raising countries of the world, especially in Australia, New Zealand, Tasmania, Turkey, Greece, etc. In India, the highest prevalence is reported from Andhra Pradesh and Tamil Nadu.  The parasite has a "dog-sheep" cycle with man as an intermediate accidental host. In humans, the most favored site for infestation is the liver (65%) or the lungs (25%); it rarely involves the brain, heart, bone, or muscle.  Injudicious approach in the management of these rare presentations may be the root cause of severe anaphylactic shock and systemic dissemination. We report an unusual case of primary hydatidosis of the calf muscles.
| Case Report|| |
A 38-year-old lady presented to surgical department with a 6 month history of painless, slow growing, enlarging swelling in her left leg and was admitted to Shri Chamarajendra Hospital, attached to Hassan Institute of Medical Sciences (HIMS), Karnataka, India. She had no history of fever or prior trauma. On physical examination, there was a soft, non-tender deep-seated mass measuring approximately 8 cm x 6 cm in size in the calf of left leg. There were no symptoms or signs of an inflammatory process. Routine laboratory tests were normal, except peripheral smear was showing eosinophilia. Plain radiographs showed only soft-tissue swelling with no bony destruction. FNAC yielded clear fluid and was inconclusive. Ultrasonography demonstrated a well-defined multi-loculated intramuscular cystic lesion measuring 7 cm x 5 cm x 3 cm. The differential diagnosis of soft-tissue tumor and hydatid cyst were offered by the radiologist. Plain chest X-rays and abdominal ultrasonography did not reveal any organ involvement. During surgery, complete excision of involved muscles was done with special attention to remove intact hydatid cysts without any breakage and spillover of contents. The diagnosis was confirmed by examination of the excised cyst.
Gross specimen examination: We received an irregular grey-brown mass measuring 8 cm x 6 cm x 4 cm. Cut open revealed intramuscular multi-loculated cystic lesion containing grey-white glistening grape-like structures of varying size [Figure 1] Cut open of grape-like membranous structures yielded a clear fluid, which was handled very carefully and collected in glass tube and centrifuged to observe under microscopy. Unstained smears of centrifuged material revealed hook lets of Echinococcus granulosus.
|Figure 1: Intramuscular multi-loculated cystic lesion containing grey-white hydatid daughter cysts of varying sizes|
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Histopathological examination revealed a laminated membrane, which was refractile, structureless, chitinous, and acellular with numerous scoleces attached to the germinative layer, which are typical of tapeworm Echinococcus granulosus organisms. A focus of dystrophic calcification of the cyst was seen, which suggests long duration of the disease process [Figure 2]. The adjacent skeletal muscle showed an extensive eosinophilic infiltration, along with lymphocytes, plasma cells, occasional foreign body giant cells, and areas of fibrosis [Figure 3] Post-operative period was uneventful, and the patient was discharged on albendazole 10 mg/kg per day for 6 weeks treatment. After follow-up of 6 months, she remained asymptomatic. Her peripheral smear was normocytic normochromic blood picture, and eosinophil count was within normal limits.
|Figure 2: Refractile, structureless, chitinous, and acellular laminated membrane with foci of dystrophic calcification (H and E, ×40)|
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|Figure 3: Hydatid membrane attached to muscle fibers with dense lymphoplasma cell infiltration and areas of fibrosis (H and E, ×20)|
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| Discussion|| |
The hydatid disease parasites are members of the flat worms (cestodes). The majority of the infestations are caused by Echinococcus granulosus and multilocularis. The parasite may affect any organ; however, muscle is supposed to be an unfavorable site for infestation because of its high lactic acid concentration.  Intramuscular hydatid cysts grow gradually and may mimic a soft tissue tumor;  thus, the diagnosis of soft-tissue hydatid cysts needs a high index of suspicion. Humans are known to be accidental intermediate hosts for Echinococcus organisms. The adult form of the parasite is seen only in dogs. The life cycle of the larva in a human ends with the bacterial infection, shrinkage of the cyst, and eventual calcification. 
Ultrasonography still remains the major non-invasive screening tool to discover the primary site of the disease and may confirm the diagnosis of hydatid disease by demonstrating the pathognomonic daughter cysts.  The CT appearance of the hydatid cyst is not diagnostic as it may mimic malignant and benign conditions such as congenital cyst, pseudocyst, or hematomas. However, the presence of daughter cysts, germinal epithelium detachment, and calcification may confirm the diagnosis. Similarly, an MRI can reveal a cystic mass containing daughter cysts, with rim sign and "Water Lilly sign."  Unfortunately, in our case, we could not get an MRI done as the patient was unable to afford it. Peripheral smear may reveal eosinophilia in only 50% of the patients, which was seen in our case. The best way to establish the diagnosis is the direct visualization of parasitic elements in the surgically resected pathological specimen.
Preoperative medical treatment may sterilize the cyst cavity and might decrease the intraoperative complication of spillage and consequential anaphylaxis. Intraoperative irrigation by 0.5% cetrimide, 15% hypertonic saline, or 0.5% silver nitrate solution, prior to cyst opening, may kill the daughter cysts and further reduces the risk of dissemination and anaphylactic reaction. Inadvertent cyst rupture releases viable scolices, which may enter the circulation, disseminate to distant organs, and reproduce asexually to form additional cysts.  The likelihood of recurrent infestation is increased after rupture of the parent cyst. In addition, leakage of cyst contents may cause an anaphylactic shock. Thus, excision of an intact cyst is usually curative, whereas cyst rupture may be fatal.
| Conclusion|| |
Hydatid disease can affect any organ in the body; the infestation may mimic a soft tissue tumor and, therefore, a high suspicion of this disease is justified in any cystic neoplasm of any organ. Intramuscular hydatid cysts grow gradually and may mimic a soft tissue tumor; thus, the diagnosis of soft-tissue hydatid cysts needs a high index of suspicion. The purpose of the present report is to alert the reader to this rare infestation so that an open biopsy will be avoided. Percutaneous needle biopsy is also not recommended because of the possibility of introducing scolices into the needle tract. The recommended treatment of Echinococcus is complete excision of the cyst lining and thorough irrigation of the cyst cavity with scolecidal agents to decrease the risk of recurrence.
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Sankappa P Sinhasan
Associate Professor, Department of Pathology, Indira Gandhi Medical College & Research Institute, Kathirkamam, Vazhudavur Road, Puducherry-605 009
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3]