A rare case of intramuscular granular cell tumor in the right thigh: case report and literature review.

Background: Granular cell tumor (GCT) is a rare soft tissue neoplasm, and granular cell tumor of the extremity (GCT-E) is even rarer. Routine laboratory examinations yield no specific findings in GCT-E, making multimodal imaging potentially valuable for preoperative diagnosis and treatment decision-making. This study aimed to analyze the clinical, imaging and pathological characteristics of GCT-E in the vastus medialis muscle, and to explore the clinical guiding value of multimodal imaging in its diagnosis and surgical treatment. Case presentation: A 49-year-old male patient was admitted to the hospital with a complaint of "a mass in the medial aspect of the right thigh for more than 1 year with progressive enlargement in the past week". Initial ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI) examinations revealed a soft tissue mass in the inferior segment of the right vastus medialis muscle. Positron emission tomography-computed tomography (PET-CT) examination showed increased fluorodeoxyglucose (FDG) metabolism, suggesting the possibility of a benign or low-grade malignant tumor. He underwent a pathological biopsy at the Second Affiliated Hospital of Zhejiang University, and the result indicated an atypical granular cell tumor. The patient received en bloc resection of the vastus medialis muscle, and the postoperative pathological and immunohistochemical findings were consistent with the biopsy diagnosis. Conclusion: GCT-E arising in the vastus medialis muscle of middle-aged males is extremely rare, and through a literature review, we summarized its imaging features and found that it is most commonly misdiagnosed as schwannoma. Multimodal imaging may assist in defining the lesion extent, ruling out distant metastasis and guiding the formulation of individualized surgical plans for GCT-E. En bloc resection of the lesion with negative surgical margins is the mainstay of treatment, and limb function should be maximally preserved while achieving radical resection. Pathological examination combined with immunohistochemical detection is the gold standard for the diagnosis of GCT-E. This case may provide a useful illustrative example for the diagnosis and treatment of such rare intramuscular soft tissue tumors.