Primary hydatid cyst of skeletal muscle: A rare clinical entity

Abstract

Introduction

Hydatid cyst is a parasitic infection caused by Echinococcus granulosus, commonly affecting the liver and lungs. Muscular involvement is extremely rare, accounting for only 0.7 % to 0.9 % of cases. This case highlights the diagnostic challenges of muscular hydatid cysts, which can mimic sarcomas, abscesses, or lipomas.

Case report

A 90-year-old female from a rural area presented with a slow-growing swelling on the posteromedial thigh for three years. She had no history of trauma or systemic symptoms. Clinical examination revealed a firm, non-tender mass. Imaging suggested a cystic lesion, and serology confirmed Echinococcus infection. Surgical excision was performed, and histopathology confirmed a hydatid cyst. The patient received a six-week course of albendazole postoperatively. Her recovery was uneventful, with no recurrence at follow-up.

Discussion

Muscular hydatid cysts are rare and often misdiagnosed as soft tissue tumors. Imaging modalities, particularly ultrasound and MRI, aid in diagnosis, while serology provides further confirmation. Complete surgical excision remains the preferred treatment, and antiparasitic therapy reduces recurrence risk.

Conclusion

Although rare, muscular hydatid cysts should be considered in the differential diagnosis of soft tissue swellings, particularly in endemic regions. Early recognition and appropriate management prevent complications and improve patient outcomes.

Highlights

• •This case presents a rare primary muscular hydatid cyst in a 90-year-old female, adding to limited literature on such cases.
• •It highlights the importance of multimodal diagnosis-imaging, serology, and histopathology- for confirming hydatid disease in atypical locations.
• •It highlights successful management with surgical excision and a six-week albendazole course, contributing to treatment strategies.

1. Introduction

Hydatid cyst also known as cystic echinococcosis is a cystic disease caused by Echinococcus granulosus, a tapeworm from the Taeniidae family. These parasites are primarily found in rural areas and harm agricultural workers who regularly come into contact with livestock [1]. The tapeworm has a complicated ecological life cycle between definitive hosts like dogs and wolves and intermediate hosts like sheep and cattle [2]. Humans, however, are accidental hosts for the illness. Definitive hosts like dogs, wolves, or foxes excrete eggs into the environment in their feces and cause the spread of the disease [3]. Thus, the prevalence of hydatid cysts is generally highest in Mediterranean nations, the Middle East, India, and Australia because of the importance of animal husbandry in these areas [3].

It can affect any human organ mostly the liver and lungs due to their rich blood supplies [4]. Nevertheless, they are very rare in the musculoskeletal system, accounting for only 0.7 % to 0.9 % of entire cases [5].

Treatment options for muscular hydatid cysts are surgical excision with anthelminthic therapy i.e. albendazole for 1–6 months postoperatively depending on the size of the cyst with the regular follow-up every 3 months to monitor the recurrence.

We report a rare case of primary muscular hydatid cyst in a 90-year-old female presenting with swelling on the posteromedial aspect of her lower thigh. Primary muscular hydatid cysts without the involvement of abdominal and thoracic organs are extremely rare. Most of the time primary muscular hydatid cysts are confused with other differentials like sarcomas, lipomas, and abscesses. [6] This case highlights the importance of considering hydatid cysts as a potential differential in muscular limb swelling. This case report follows the SCARE criteria. [14]

2. Case presentation

A 90-year-old female with hepatitis C and a 60-year smoking history from a rural area presented with swelling on the posteromedial aspect of the left thigh just above the knee. The swelling was first noticed 3 years ago and gradually increased in size over this period. She felt mild discomfort but denies any associated symptoms of pain, itching, discharge, fever, or joint immobility. As she was from a rural area she also had a history of animal exposure.

On physical examination, the swelling was 14 × 10 spherical in shape, firm, fixed, and nontender with well-defined margins seen on the posteromedial aspect of the left thigh just above the knee. The overlying skin was pinchable and showed prominent veins, and the temperature was comparable to the surrounding skin.

Ultrasound revealed a large cystic lesion with several small cysts inside it measuring 13.2 × 11 × 13.6 cm and a volume of 1046 ml. It was arising from the left knee joint and was extending into mid-thigh. Color Doppler showed no vascularity inside it. MRI was done and showed a large cystic lesion (21 × 9.9 × 8.1 cm) with multiple small scattered lesions with both intramuscular and intermuscular extension involving adductor longus and gracilis medially and bicep femoris posteriorly as shown in Fig. 2. All these features were suggestive of a hydatid cyst. The diagnosis was confirmed by a hemagglutination test for Echinococcus. X-ray chest and ultrasound of the abdomen were normal.

Fig. 2.

A well-defined cystic lesion with multiple daughter cysts.

Surgical excision of the cystic swelling was planned, and an S-shaped incision was made on the skin, followed by careful dissection through the subcutaneous tissue to access the cyst. The lesion was well-defined within the inter- and intramuscular planes. Meticulous dissection was performed to isolate and remove the cyst intact, ensuring no spillage of its contents. To minimize the risk of contamination, the surgical site was thoroughly irrigated with normal saline following excision.

Intraoperative findings revealed a large intermuscular cystic swelling measuring 22 × 14 cm, involving the posterior and medial compartments of the left thigh. The cyst demonstrated intramuscular extension into the adductor longus and gracilis medially and the biceps femoris posteriorly, extending up to the popliteal fossa, as shown in Fig. 1. Notably, there was no communication between the cyst and the knee joint. A biopsy sent to the lab further confirmed the diagnosis. Histopathological examination of the excised specimen revealed a fibrocollagenous cyst wall lined by attenuated epithelium with inflammatory infiltration. The presence of focal keratinous material further characterized the lesion. These findings, along with gross features, favored the diagnosis of a hydatid cyst. The postoperative course was uncomplicated and the patient was discharged with anthelminthic therapy for six weeks. Follow-up visits were scheduled at one week, three weeks, six weeks, nine weeks, and twelve weeks. During these visits, the patient showed no signs of recurrence or complications.

Fig. 1.

Gross specimen of the excised hydatid cyst.

3. Discussion

Hydatid cyst is a zoonotic disease caused by a tapeworm, Echinococcus granulosus. This cestode parasite is found all around the world, but it is most prevalent in pastoral and poor rural areas where people keep animals in close proximity to dogs. It is mostly prevalent in Mediterranean nations, the Middle East, India, Australia, and South America [7]. In intermediate hosts like humans, the transmission occurs through the orofecal route. After absorption from the intestine, the larvae of Echinococcus oncospheres, which originate from parasite eggs, pass through the intestinal wall and enter the liver and other organs through the portal vein [8]. The liver and lungs are the most frequently affected organs in the human body.

Although hydatid illness can impact any organ in the body, it is very uncommon for a primary hydatid cyst to develop in soft tissue and muscle without signs of liver or lung disease. Because of the extensive capillary filtration system in the lungs and liver, it is very difficult for echinococcal larvae to reach from portal vein to systemic circulation after intestinal absorption [9]. Furthermore, because of the high content of lactic acid and the mechanical activity of muscles make them unfavorable for parasite growth [10].

Our case presented with a primary hydatid cyst in an intermuscular compartment of posteromedial thigh with intramuscular extension in the bicep femoris posteriorly and adductor longus and gracilis medially, reaching the popliteal fossa. Normally hydatid cysts in muscle arise secondary to dissemination from the liver or other organs but primary muscular hydatid cyst is an extremely rare condition with only a few cases reported in the literature. By documenting these types of cases, we can gain a better grasp of this disease, including its clinical manifestations, diagnosis, and treatment.

Preoperative diagnosis of hydatid cysts is crucial as this condition should be differentiated from diseases with similar presentation. Indirect hemagglutination test and ELISA are the initial screening tests but they are more sensitive for liver hydatid cysts. Moreover, serological tests alone are not enough to diagnose echinococcus [11]. Other modalities which are used to diagnose hydatid cysts are imaging modalities including ultrasound, CT, and MRI. MRI is considered the best diagnostic tool in diagnosing muscular hydatid cysts as it provides extensive information regarding their structure and extension [12]. Regarding the treatment of hydatid cysts, it mostly depends on the site of a cyst, its relation to other structures, or its systemic involvement. Four different treatment approaches are being used all over the world: (1) surgery, (2) puncture, aspiration, injection of protoscolicidal agent and re-aspiration (PAIR), (3) chemotherapy with albendazole or mebendazole, and (4) watch and wait [13]. The recommended course of therapy for a muscular hydatid cyst is a total surgical excision of the cyst without exposing the cavity to prevent contents from spilling. The use of pre-operative and post-operative antihelminthic chemotherapy reduces the rate of recurrence of hydatid cysts. Continuous clinical assessment is required after surgery to check for recurrence. The work has been reported with the SCARE criteria. [14]

4. Conclusion

This case brings attention to the unusual occurrence of primary muscular hydatid cysts, especially when there is no involvement of the liver or lungs. The patient's history of a slow-growing, painless swelling on the posteromedial thigh created a diagnostic challenge, as it closely resembled other conditions like sarcomas, lipomas, or abscesses. It's essential to keep hydatid cysts in mind as a possible cause of unusual limb swellings, particularly in areas where the disease is common or when there's a history of exposure to animals.

Consent

Informed consent was taken from the patient.

Ethical approval

Ethical approval is not required, as the study is exempt from ethical approval for case reports in our institution.

Guarantor

Ahmad Ismail

Sources of funding

There are no sources of funding in this study.

Author contribution

All authors contributed to the study design, writing of manuscript, editing, and proof reading. Each

author gave approval of the final manuscript.

Declaration of competing interest

There are no conflicts of interest in this case report.