Intermuscular hydatid cyst in the thigh musculature: a case report

Abstract

Introduction

Echinococcus granulosus, a tapeworm, is responsible for causing hydatid disease. Hydatid cysts rarely affect the musculoskeletal system, occurring in less than 5% of cases. This case report presents the clinical presentation, diagnosis, and management of muscle echinococcosis.

Case presentation

A 28-year-old Black African female presented with a 4-month history of left anteromedial thigh swelling. Despite mild burning pain, she remained functional. While pyomyositis was initially considered, ultrasound and magnetic resonance imaging suggested hydatid disease. Surgical excision was performed, and histopathology confirmed the diagnosis. The patient received albendazole and praziquantel for 4 and 2 weeks, respectively, as adjunctive therapy. A year-long follow-up revealed good progress and continued health.

Conclusion

Primary muscle hydatid cysts should be considered in the differential diagnosis of cystic, painless, localized masses in the muscular system, especially in endemic regions. Serological tests and imaging techniques are essential for investigation. Complete surgical excision and anthelminthic therapy should be pursued when possible.

Introduction

Cystic echinococcosis, also known as hydatid disease or hydatidosis, is a parasitic and zoonotic disease affecting both animals and humans. It is typically caused by the Echinococcus granulosus tapeworm, although the Echinococcus multilocularis tapeworm can also cause this disease. The liver and lungs are the most common sites of infection, while musculoskeletal involvement is exceptionally rare, occurring in only approximately 0.5–4% of patients [1].

Infection with Echinococcus granulosus begins when the definitive host, typically a dog, ingests the ova. Humans, the intermediate host, are accidentally infected. The ova hatch into embryos in the duodenum, as they are resistant to stomach acid. These embryos penetrate the duodenum and enter the portal vein system, where they are transported to the liver. Hydatid cysts most commonly develop in the liver and lungs, although they can also occur, though rarely, in various muscles, including the biceps femoris, triceps, supraspinatus, diaphragm, psoas, sartorius, thigh, quadriceps femoris, and gracilis. Hydatidosis, a significant public health issue in developing countries, is driven by factors such as illegal animal slaughter, a high number of stray dogs, and inadequate public awareness about hydatid disease [2].

The thigh musculature was the most frequent location for hydatid cysts, followed by the paravertebral region. The most common presentation was a painless, slow-growing mass with normal overlying skin. Total surgical excision and fine-needle aspiration were the primary treatments. Therefore, primary muscle hydatid cysts should be the priority differential for such presentations, especially in endemic areas. Serological tests and imaging modalities should be used for investigation [3].

This disease is highly prevalent in many parts of the world, especially in South America, the Middle East, some African countries, Australia, and the Mediterranean [4]. Hydatid cysts in skeletal muscle are often misdiagnosed as malignancy or pyogenic infection, such as pyomyositis, due to nonspecific imaging findings. Preoperative diagnosis is challenging due to low prevalence and similarity to other soft tissue masses. Diagnosis is frequently made intraoperatively or after histological examination. Calcification on computed tomography (CT) scans and the presence of multiple primary cysts can help differentiate them from carcinomas, amoebic abscesses, bacterial abscesses, and hemangiomas [5]. Moreover, hydatid serology often yields negative results. The main management method for skeletal muscular hydatidosis is surgery. However, there is an increasing use of adjuvant chemotherapy, such as albendazole [6]. We report a patient with skeletal muscle hydatid disease who was treated surgically and with a combination of albendazole and praziquantel postoperatively. Due to a lack of such case reports in the local area, there is a significant knowledge gap regarding clinical presentation, diagnosis, and management. Therefore, this report will provide a basis for clinical suspicion of skeletal muscle hydatid disease.

Case report

A 28-year-old Ethiopian woman was admitted to the orthopedic department complaining of swelling in the left thigh. She had noticed swelling 4 months prior. She had mild burning thigh pain; otherwise, she was able to perform her daily activities without any difficulties. She had no history of fever or trauma to the thigh. She and her family had no history of chronic illnesses or similar conditions in the past. She grew up in a rural area of Ethiopia where there were domestic animals such as sheep and dogs. For her complaint, she visited a local health center where she was prescribed an unknown oral medication for 7 days, but it did not lead to any improvement. On examination, she was not febrile; there was a 10 cm × 12 cm non-tender mass over the anteromedial left thigh. It was soft in consistency and not clearly delineated from deep structures. There was no scar, skin color change or any engorged veins (Fig. 1).

Fig. 1

Left anteromedial thigh swelling; Tibebeghion Specialized Hospital, Bahirdar; 2020

The investigations revealed a normal total white blood cell count, eosinophilia of 1.7%, and an erythrocyte sedimentation rate of 50 mm/hour. Diagnostic ultrasound, computed tomography (CT), CT angiography, magnetic resonance imaging (MRI), and histopathology were performed. Thigh radiography was also performed (Fig. 2).

Fig. 2

Left thigh X-ray showing increased soft tissue density on the medial and proximal parts of the thigh with displaced otherwise preserved fat planes. The femur appeared normal

The initial ultrasound result suggested abscess collection, so left thigh pyomyositis was considered, and the abscess was aspirated. Aspiration revealed fluid other than pus. Repeated ultrasound revealed findings consistent with hydatid cysts in the muscle (Fig. 3).

Fig. 3

A 28-year-old female with a ruptured hydatid cyst in the left thigh muscle. Ultrasound linear and curvilinear images showing the pericyst (blue star) and detached floating membranes (green arrows) within the thick hypoechoic fluid (blue cross). The detached endocyst with coiled margins (blue arrow) resembles a “scroll.” The color Doppler image in C shows the avascular nature of the detached membranes

MRI of different sections also revealed features of ruptured cysts in the musculature of the left thigh (Figs. 4, 5, 6, and 7).

Fig. 4

A 28-year-old female with a ruptured hydatid cyst in the left thigh muscle. A Coronal T1-weighted and B coronal T2-weighted images showing large, well-defined T1-weighted hypo-intense and T2-weighted hyperintense cystic intramuscular hydatid cysts with intermediate to hyperintense T1-weighted and hypo-intense T2-weighted walls representing the pericyst (blue arrow). There is also a T1-weighted hyperintense small lesion (curved green arrow) representing calcification

Fig. 5

A 28-year-old female with a ruptured hydatid cyst of the left vastus medialis muscle. Both T1-weighted (C) and T2-weighted (D) axial images show a hypo-intense collapsed floating membrane known as the floating membrane sign or water lily sign (blue arrow). It is pathognomonic of a hydatid cyst, representing the detached endocyst within the large cyst, consistent with a ruptured hydatid cyst

Fig. 6

A 28-year-old female with a ruptured hydatid cyst in the left vastus medialis muscle. Coronal T2-weighted fat-suppressed image showing perilesional hyperintensity representing perilesional edema (thin black arrow) (E). The sagittal postcontrast T1-weighted image shows intense smooth thick wall enhancement (black curved arrow) (F) compared with the sagittal precontrast T1-weighted image (G)

Fig. 7

Computed tomography angiography (CTA) of bilateral lower extremity showing normal angiography

Considering the presence of a benign lesion in the thigh (a hydatid cyst), surgery was planned. The intraoperative finding was a cystic mass arising from the vastus medialis and intermedius. A ruptured cyst with floating whitish leaf-like tissue and turbid fluid was observed. The mass was removed with its shell and sent for histopathology study (Figs. 8 and 9). The wound was washed with hydrogen peroxide and normal saline solutions.

Fig. 8

Intraoperative image after the cyst was excised showing a bare femur. The cyst was adherent to the periosteum of the femur

Fig. 9

A—Floating membrane. B—Whole cyst sliced in half showing a compartmentalized ruptured cyst

Histopathology revealed layers of amorphous material, and the hook left was consistent with an intramuscular hydatid cyst.

Postoperatively, the patient was started on adjunctive therapies of albendazole 400 mg twice daily orally for 4 weeks and praziquantel 800 mg three times daily orally for 2 weeks. The patient was followed for one year, and she was performing her daily routine activities without complaints.

Discussion

Echinococcosis, a parasitic zoonotic disease affecting both animals and humans, is typically caused by the Echinococcus granulosus tapeworm. It is a significant public health concern due to the parasite’s complex life cycle, presence of various strains, and challenges in timely diagnosis and treatment for both humans and animals.

Echinococcosis primarily affects the liver and lungs, which are the organs most commonly reached by the ova from the duodenum. Musculoskeletal involvement is exceptionally rare, occurring in only 0.5–4% of cases [1]. Most case studies of muscle-only hydatid cysts report a painless mass that gradually grows. However, in some cases, multiple muscles and surrounding tissues, including bones, can be involved, leading to compressive symptoms [5]. Therefore, Echinococcosis should be considered in the diagnosis of slowly growing soft tissue masses in patients from endemic areas [7]. Possible differential diagnoses include lipomas, calcified old hematomas, cold abscesses (tuberculosis), and soft tissue tumors.

The diagnosis of hydatid cysts is based on epidemiological data, medical history, clinical symptoms, laboratory results, and immunological tests [5]. Accurate preoperative diagnosis, without biopsy or aspiration, is crucial to prevent local recurrence, cyst infection, and fatal anaphylactic reactions. Ultrasound examination is highly sensitive in typical cases. CT and MRI can also provide detailed information about the lesion [4].

Our patient presented with compressive symptoms and a gradually enlarging mass that did not interfere with daily activities. As a rural woman, she was susceptible to contributing factors. Ultrasound and MRI strongly supported the diagnosis of hydatid disease. Complete surgical resection is curative for intramuscular hydatid disease. In our patient, surgical excision was performed, followed by adjunctive therapy with albendazole and praziquantel. Subsequent follow-ups showed significant improvement with no complications.

Limitations of the case reports included difficulty in obtaining local publications and the patient's distance from the study area, which made frequent follow-up challenging.

Conclusions

Echinococcosis, a parasitic zoonotic disease, rarely affects the musculoskeletal system. Skeletal muscle cysts are often misdiagnosed as malignant or pyogenic infections and can be challenging to diagnose. While rare even in endemic areas, hydatid disease in muscular tissue should be considered as a differential diagnosis for any soft tissue or muscle-bone mass. Surgery, with or without antihelminthic drugs such as albendazole and praziquantel, is the primary treatment option.