A 53-year-old male presented with a mildly painful right thigh swelling for the past three months. There was no history of trauma, surgery or additional diseases.
On physical examination, a palpable mass was noted with an approximated length of 6cm and there were no signs of inflammation of the skin or lymphadenopathies.
Initially, a US was performed revealing a large multilocular cystic mass, with some echogenic debris inside. It was localized in the medial side of the right thigh and showed no significant Doppler signal (figure 1).
On MRI, a well-defined multicystic encapsulated mass was found on the right adductor muscles. Measuring 6, 9 x 6, 7 x 18, 2 cm (antero-posterior x transversal x longitudinal), it showed homogeneous low signal characteristics on T1-weighted images and very high signal on T2-weighted images, separated by thick septa, with no solid component (figure 2). On T1-weigthed images and fat suppressed T1-weighted images, the lesion had no loss of signal intensity (figure 3). Dynamic contrast-enhanced MR images only showed enhancement of the peripheral capsule (figure 4).
Adjacent to the lesion, smaller rounded cysts were found, compatible with daughter cysts (figure 5). No apparent relation with neurovascular or bone structures were found.
Hydatid disease (HD) is an endemic infestation caused by the tapeworms of the echinococcus, humans being accidental hosts in their life cycle. Found in the intestine of carnivores, when humans are infected, the development of a hydatid form occurs, especially in the liver and lungs [1].
HD can be either primary or secondary. In the secondary form, there is an actual or previous primary location of a hydatid cyst in the liver, lung or spleen. Primary muscular localization of HD represents 0,9% of cases [2], not only because the sole implantation at this localization involves passage through the filters of the liver and lung but also due to muscle contractility and presence of lactic acid. The muscle volume and its rich blood supply could explain predilection for proximal muscles of the lower limbs [3].
The symptoms include a slow-growing soft tissue mass, which can be associated with pain or inflammatory signs.
Imaging modalities play a major role in the diagnosis of these lesions. The first, most affordable and noninvasive exam to perform is Ultrasound, where the presence of cystic formations with daughter cysts, detached membranes and double-line sign are the characteristic features of these lesions. The sensitivity of US is 95% and can reach 100% if vesicular fibrils are present [4].
Gharbi classification based on their ultrasound features, divides them into 5 types [5]:
• I–Unilocular unechoic cystic lesion with double line sign
• II–Fluid collection with a split wall (water lily sign)
• III–Fluid collection with multiple septa/and/or daughter cyst (honeycomb sign)
• IV–Heterogeneous cyst contents with internal echoes
• V–Cyst with reflecting calcified thick wall
Computed tomography appearance can range from a unilocular cyst to a complex or a solid lesion, mimicking a tumour. On CT one can depict wall calcifications, the presence of daughter cysts and detached membranes [6].
Magnetic resonance imaging T2 sequences show a multilocular cystic formation with low intensity rim, representing the pericyst, which is rich in collagen and is generated by the parasite. A low-intensity rim (rim sign), seen on both T2 and T1 sequences, is a characteristic sign in muscular HD. A feature that is rarely found in HCs located in other regions of the body [7].
Complete surgical removal of the cyst remains the primary treatment option [8].
HD imaging features contribute to the pre-operative diagnosis and can also prevent the use of aggressive diagnostic tools such as fine needle aspiration or core needle biopsy, thus reducing the risk of anaphylactic shock or dissemination of viable parasites [9].
Primary Muscle Hydatid Disease
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Based on ultrasound, CT, and MRI scans, a cystic lesion measuring approximately 6 cm is observed within the right thigh muscle, showing a multilocular pattern. Ultrasound images reveal multiple cystic structures as well as features resembling “daughter cysts,” a “honeycomb” appearance, or a “water lily” sign. CT indicates possible calcification or membrane detachment in part of the cyst wall. On T2-weighted MRI, the lesion appears as a multicystic high signal with a peripheral low-signal rim (“rim sign”), suggesting a thick fibrous capsule. The surrounding muscle structures remain intact, with no obvious bone involvement, cortical destruction, or significant lymph node enlargement detected thus far.
From the clinical and imaging findings (multiple cystic components, internal daughter cysts, etc.), parasitic infection such as hydatid disease is most suggestive. Other soft-tissue tumors or chronic infectious granulomas generally do not fit well with the “multiple cystic cavities” and “distinct cyst wall” features.
Considering the patient is a 53-year-old male with a gradually enlarging mass in the right thigh, imaging findings of “multicystic lesions” and “daughter cysts,” plus histopathological evidence of a fibrous capsule and cystic spaces, the most likely diagnosis is:
Primary Muscular Echinococcosis (Hydatid Disease).
Further confirmation may involve serological tests (detection of echinococcus-related antibodies), imaging follow-up, or surgical excision with pathological examination.
The primary treatment is surgical resection of the lesion, with adjunct antiparasitic medication (such as albendazole) when necessary to reduce the risk of recurrence or spread. Specific suggestions include:
Regarding rehabilitation and exercise prescriptions, these should be tailored to the patient’s postoperative status and individual fitness level, following a gradual and personalized approach:
FITT-VP Principle: When implementing an exercise program, adjust the frequency, intensity, time, type, and volume/progression to the individual patient’s condition. For example, 3–5 sessions per week, each lasting 20–30 minutes, beginning with low-intensity activities (such as light resistance band training or mild cycling). Exercise load and duration can then be increased gradually based on recovery progress.
Disclaimer: This report is for reference only and cannot replace a face-to-face consultation or professional medical advice. Please consult your physician or a qualified specialist for specific diagnosis and treatment.
Primary Muscle Hydatid Disease
