International Journal of Innovative Research in Medical Science (IJIRMS) Volume 09, Issue 05, May 2024, https://doi.org/10.23958/ijirms/vol09-i05/1888 www.ijirms.in 295 Case Report A Primary Hydatid Cyst of Thigh Mimicking as Soft Tissue Tumour: Diagnostic Dilemma Dr Nitin Sherkar * 1 , Dr Bhupendra Mehra 2 , Dr Siddharth P. Dubhashi 3 , Dr Senthilkumaran K 4 , Dr Vinod Pusdekar 1 , Dr Ateet Fulmali 5 1 Assistant Professor, Department of Surgery, AIIMS Nagpur, Maharashtra, India. 2 Additional Professor, Department of Surgery, AIIMS Nagpur, Maharashtra, India. 3 Professor and Head, Department of Surgery, AIIMS Nagpur, Maharashtra, India. 4 Associate Professor, Department of Surgery, AIIMS Nagpur, Maharashtra, India. 5 Junior Resident, Department of Surgery, AIIMS Nagpur, Maharashtra, India. *Corresponding author: Dr Bhupendra Mehra; drbmehra@aiimsnagpur.edu.in Received 17 April 2024; Accepted 12 May 2024; Published 14 May 2024 Abstract Hydatid disease is one of the most prevalent parasitic infections caused by Echinococcus granulosus. It is likely to affect all organs. However, primary hydatid cysts of muscle tissue are so uncommon. A timely and precise diagnosis is critical to avoiding an unnecessary biopsy. Here, we present a case of a 29-year-old female presented with soft tissue swelling over the anterior aspect of the right thigh. The diagnosis of a hydatid cyst was made based on ultrasonography (USG) and magnetic resonance imaging (MRI). A complete surgical excision of the cyst was done with an uneventful postoperative course. Keywords: Hydatid disease, Echinococcus granulosus, intramuscular hydatid, Magnetic Resonance Imaging. Introduction Hydatid cysts are parasitic infections transmitted to people by dog faeces, and they are common in places where agriculture and livestock breeding are practiced. The most common causative agent is Echinococcus granulosus [1] . The liver and lungs are the two most often affected organs in humans, as ingested eggs hatch in the intestines and go to the liver via the portal system. Embryos that escape the hepatic filter are delivered to the right heart via venous circulation and then to the lungs. If embryos exit the pulmonary circulation and enter the left heart chamber, the arterial circulation can transport them to any part of the body. Echinococcosis may also affect the brain, heart, kidney, ureter, spleen, uterus, fallopian tube, mesentery, pancreas, diaphragm, and muscles [2] . Musculoskeletal involvement is uncommon, accounting for just 1-5.4% of musculoskeletal hydatid cyst cases. Because of the low prevalence and similarity of these lesions to soft tissue masses, pre-operative diagnosis is challenging in this condition. In many cases, the diagnosis is confirmed intraoperatively or after histological examination [3] . Case report A 29-year-old female patient presented with swelling over anterior aspect of the right thigh for 1 year. On local examination, there was 20x15 cm intramuscular swelling present over anterior aspect of right thigh, and firm in consistency (Figure 1). All biochemical parameters were within normal limits. In clinical suspicion of soft tissue tumour of right thigh ultrasonography was done and it showed a large oval shaped hypoechoic lesion of size 14.8x8.3x4.5 cm with multiple thin walled, variable sized clear cysts in intramuscular plane (Figure 2). Contrast-enhanced MRI revealed a 24×10x8 cm cystic lesion with multiple daughter cyst in vastus muscle of right thigh (Figure 3). Ultrasonography of abdomen and chest was done to see the presence of hydatid cyst in peritoneal and pleural cavity, which was normal. Pre-operatively patient was started tab albendazole 400 mg BD for 15 days. Excision of entire cyst with hydatid sand was done (Figure 4). Intra-operative and postoperative course was uneventful. Postoperatively patient was again started on tab albendazole 400 mg BD.