Muscle localization of hydatid disease is rare. The diagnosis is confirmed by imaging and the treatment is surgical. We report a case of primary muscle localization of the thigh.

This concerns a 36-year-old patient, B.B., originating from a rural area, with no particular medical history, who presented with a mass in the left thigh that had been evolving for 6 months, gradually increasing in volume without fever or alteration of general condition.

Clinical examination revealed a swelling on the antero-internal side of the left thigh, renitent, mobile, and painful, with a diameter of 5 cm.

Ultrasound revealed a well-defined heterogeneous intramuscular formation with the presence of calcifications. MRI revealed a multi-locular mass of the left vastus muscle measuring 48x51mm, with a heterogeneous extent of 77mm, suggesting a hydatid cyst.

Chest X-rays and abdominal ultrasound were normal. There were no other hydatid localizations, and hydatid serology was negative.

Surgical excision was performed as a total pericystectomy on a closed cyst.

The anatomical pathology examination of the excised tissue confirmed the diagnosis of hydatidosis.

Figure: Amultilocular mass of the vastusintermedius muscle measuring 48x51 mm extended over 77 mm in heterogeneous height suggestive of a hydatid cyst.

Hydatidosis is a disease caused by the development of the larval form of the dog tapeworm called Echinococcus Granulosus, where humans are intermediate hosts [1]. There is no predilection for gender or age. It is an endemic disease in many countries, as is the case in North Africa [2].The most frequent localizations are the liver (60%) and the lungs (20%).

Muscular involvement is rare, even in endemic countries, representing 1-5% of all hydatid localizations [3, 4, 5]. The diagnosis benefited from imaging, which plays a crucial role in confirming the positive diagnosis.

Soft tissue ultrasound is the first-line examination, characteristics are precisely described according to GHARBI's classification (6).

MRI plays an important role in the hydatid pathology of soft tissues. Its high-resolution contrast allows a better study of the loco-regional extension of the lesion and its vasculo-nervous relations, while offering a detailed analysis of the cyst walls (7).

Surgery remains the essential treatment in hydatidosis, with the intervention of choice being total pericystectomy with a closed cyst.

Muscular localization of the hydatid cyst is rare, and the diagnosis should be considered in any muscle mass from patients originating from areas with high endemicity. MRI is the diagnostic method of choice.

Pericystectomy is the standard procedure.

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