Hydatid disease is a zoonotic disease caused by tapeworms, with the most common type being Echinococcus granulosus. It is primarily found in Mediterranean countries, the Middle East, South America, and East Africa (2, 3). While hydatid disease can affect any organ in the human body, the occurrence of a primary hydatid cyst in soft tissue and muscle without evidence of disease in the liver or lungs is extremely rare (4-6). The effective filtration of the liver and lungs makes it difficult for echinococcal larvae to reach musculoskeletal tissues. Moreover, the high lactic acid content and mechanical factors, such as contraction activities, make muscles unsuitable for the growth of parasites (7, 8).
In cases of soft tissue echinococcosis, a palpable slow-growing mass is the most common clinical finding. The clinical manifestations are caused by compression of the affected organ (9). However, to the best of our knowledge, there have been no previous reports of hydatid cysts in muscle tissue presenting with peripheral nerve symptoms as the initial manifestation. In the present case, the patient's main symptom was numbness in the sole of the right foot and right calf. Clinicians often face challenges in diagnosing hydatid cysts in muscle tissue, as the peripheral nerve symptoms can be nonspecific. We believe that the numbness in the plantar region of this patient's foot is primarily due to the presence of a large hydatid cyst located between the posterior tibial muscle and soleus muscle, which compresses the tibial nerve and its branches. The nerves supplying the ankle and foot originate from the calf, and they mainly stem from the lumbosacral nerve plexus, particularly the tibial nerve, peroneal nerve, and saphenous nerve. The tibial nerve is a continuation of the sciatic nerve trunk. In the popliteal fossa, the tibial nerve runs alongside the popliteal artery. In the lower leg, it descends deep within the soleus muscle in tandem with the posterior tibial artery, eventually wrapping around the posterior aspect of the medial malleolus. It further divides into the lateral plantar nerve and the medial plantar nerve. During its descent, the tibial nerve innervates all the posterior muscle groups and supplies the plantar muscles. The tibial nerve gives rise to numerous terminal branches within the ankle canal, and it, along with its branches, plays a crucial role in the development of pain, coldness, and numbness associated with the mid and hindfoot.
Preoperative diagnosis of hydatid disease is critical to avoid cyst rupture and dissemination, leading to recurrence. Percutaneous needle biopsy should mostly be avoided. Although hydatid disease rarely involves soft tissues, it should be considered in the differential diagnosis of soft tissue masses in the musculoskeletal system (10-12), especially when dealing with patients from zoonotic endemic areas. A detailed history, including residence and exposure to infectious diseases, is also necessary.
Serology alone is insufficient to diagnose echinococcosis (13). The diagnosis relies on identifying a hydatid cyst in tissues. Utilizing all available imaging methods significantly contributes to the preoperative diagnosis. Different imaging modalities are complementary and often provide a definitive preoperative diagnosis (9). Ultrasound and CT imaging can reveal a calcified cyst wall, microcalcifications in daughter cysts, and different fluid densities between the cysts and surrounding organs (9, 14). MRI is the preferred examination when hydatid disease is suspected. Classic MRI findings include a multivesicular cyst, an intense rim on T2-weighted images, or a detached membrane (15-18). The MRI scan demonstrated a multilocular lesion with several daughter cysts inside a mother cyst.
The choice of treatment modalities depends on the cyst's anatomical location, its relation to major anatomical structures, the number of cysts, the patient's general health status, and the surgeon's experience (18, 19). Surgery is the preferred therapeutic approach for muscular hydatid disease. During the operation, the surgical field should be fully exposed, and the outer capsule should be gently separated for complete resection while keeping the outer capsule intact. Care must be taken to prevent anaphylactic shock caused by cyst fluid leakage. Scar tissue can be removed as well. Additionally, thoroughly rinsing the surrounding soft tissues with hypertonic saline helps prevent recurrence. In inoperable cases, percutaneous aspiration, infusion of scolicidal agents, and reaspiration (PAIR), guided by imaging (ultrasound or CT), can be used as an alternative to surgery (18, 20). Postoperative albendazole therapy is typically given for six weeks to reduce the risk of recurrence (21). Long-term clinical evaluation is necessary after the operation to check for recurrence.
Based on the findings of this case, we emphasize considering hydatid disease in the differential diagnosis of soft tissue masses in the muscular system, particularly in endemic areas. It's also important to be aware that patients may seek medical attention with atypical complaints, such as peripheral nerve symptoms.