Intratendinous Calcified Chondroid Mesenchymal Neoplasm: A Case Report.

Introduction: We present a case report concerning calcified chondroid mesenchymal neoplasms (CCMN), a novel category of tumors that exhibit chondroid formation and contain fibronectin 1-receptor tyrosine kinase fusions. Case Report: Our report focuses on a 73-year-old female patient who presented with pain in her right hip and gluteal region. Initially, the condition was misdiagnosed as calcific tendinitis based on X-ray imaging. However, a subsequent magnetic resonance imaging (MRI) revealed a solid lobulated mass originating from the right hamstring tendon origin, exhibiting heterogeneously hypointense T1-weighted signal, heterogeneously isointense proton density fat-suppressed signal, and heterogeneous contrast-enhancement compared to skeletal muscle. Further, investigation through computed tomography (CT) demonstrated intratumoral calcifications accompanied by erosive changes in the adjacent right ischial tuberosity. Histologic examination of a CT-guided biopsy confirmed the presence of large calcium pyrophosphate crystal deposits, along with benign chondroid tissue, thus supporting the diagnosis of CCMN. Notably, there is considerable overlap in the imaging characteristics of CCMN and the more commonly encountered calcific tendinitis (calcium hydroxyapatite depositional disease). Contrast-enhanced MRI findings play a crucial role in distinguishing between these two conditions. Conclusion: To the best of our knowledge, this is the first documented report describing the imaging features of CCMN across multiple modalities, including radiography, CT, and MRI.