Intramuscular Sparganosis in the Gastrocnemius Muscle: A Case Report
A 77-year-old man was referred to our clinic from a private clinic because of a suspected soft tissue tumor. The patient had a 6-month history of a mass over the right posteromedial aspect of the proximal tibia. Physical examination revealed a 3 cm×1 cm, soft, non-tender mass at the posteromedial aspect of the right proximal tibia, and the mass was freely mobile and easily compressed. Another mass was found at the posterior aspect of the right proximal tibia. He had pulmonary tuberculosis when he was 30 years old, for which he was treated and believed to have been cured. He also had the history of lobectomy because of a lung cancer in the left lower lobe at the age of 47 years and received a total gastrectomy due to an advanced gastric cancer at the age of 71 years.\nRoutine laboratory test results were unremarkable, and no eosinophilia was noted. Plain radiographs of the right leg revealed multiple calcifications extending from the medial part of the knee to the calf. Ultrasonography revealed a heterogeneous, hyperechoic mass with a hypoechoic tubular lesion in the gastrocnemius muscle (), and MRI revealed multiple tubular and cystic lesions in the gastrocnemius muscle. The lesions showed high signal intensity on T2-weighted images and multilobulated, peripheral enhancing low signal intensity on T1-weighted images (). The patient was a farmer, and he had occasionally ingested raw snake meat when he was young. Preoperative serodiagnosis of human sparganosis by using a monoclonal antibody-based competitive ELISA was positive (3.79 in OD value) (negative < 1.00).\nAfter preoperative ultrasound-guided marking for suspected cystic lesions, a longitudinal incision was made on the posterior aspect of the proximal tibia. A white, shiny, synovium-like piece of tissue emerged from the incision, and this was identified as a sparganum that measured 30 cm in length and 0.5 cm in width and was wriggling after removal from the patient (). The calcified foci near the calf were also removed, and these tracts possibly represented the pathway along which the larvae had passed.\nSixteen months after the operation, the patient revisited our hospital because of pain and paresthesia of the right thigh and a mass at the posterior aspect of the right distal thigh. Physical examination revealed generalized pain and a tingling sensation on the right thigh and multiple soft, mobile, non-tender masses at the posterior aspect of the right proximal tibia. MRI revealed a 1.8 cm-sized, well-circumscribed round mass arising at the right distal sciatic nerve. The lesion showed heterogeneous high signal intensity on T2-weighted images and intermediate signal intensity on T1-weighted images with a target sign or a fascicular sign, and a benign neurogenic tumor, such as a schwannoma or neurofibroma, was suspected (). Multifocal tubular and cystic lesions were also detected around the mass, showing high signal intensity on T2-weighted images and low signal intensity on T1-weighted images ().\nAn excisional biopsy was performed, and a histologic analysis revealed a schwannoma showing spindle tumor cells in a palisading pattern (). In the operative field, approximately 1 cm near the mass, several spargana worms were detected and removed at the same time.