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Background: Calcific tendinitis is a common musculoskeletal disorder found in up to 40% of symptomatic shoulders, yet its atypical presentation with intraosseous migration of calcium hydroxyapatite frequently simulates aggressive bone neoplasms or osteomyelitis on MRI. This diagnostic pitfall can trigger unnecessary biopsies, oncologic referrals, and patient anxiety, despite the condition being a benign, self-limiting entity responsive to conservative management.

Objective: To illustrate the spectrum of atypical imaging presentations of calcific tendinitis with osseous involvement and to propose a systematic multimodality diagnostic framework that distinguishes this benign inflammatory process from neoplastic or infectious mimics.

Methods: We performed a retrospective IRB-approved review of cases of calcific tendinitis with intraosseous migration imaged at our institution. Radiographs, CT, and MRI studies were analyzed to characterize pathognomonic imaging features, correlate findings across modalities, and develop a structured diagnostic algorithm for edema-dominant entheseal lesions.

Results: Pathognomonic hallmarks of calcific tendinitis with osseous involvement include an enthesis-centered distribution, focal T1 and T2 signal voids representing the calcific deposit, geographic reactive marrow edema, and smooth cortical scalloping without an associated soft tissue mass. Standard MRI is relatively insensitive (~59%) for calcium detection; extensive reactive marrow edema frequently eclipses a small or MRI-occult calcific nidus, producing a "pseudo-aggressive" appearance that mimics sarcoma, lymphoma, or osteomyelitis. Radiographic or CT correlation is essential for confirmation, as subtle amorphous mineralization, compensatory sclerosis, and smooth bony remodeling favor a chronic inflammatory rather than neoplastic process. Our proposed algorithm integrates MRI signal characteristics, cross-modality correlation, ACR Bone-RADS short-interval surveillance (6–8 weeks), and clinical context to triage indeterminate lesions.

Conclusion: Recognition of the pseudo-aggressive imaging features of calcific tendinitis with intraosseous migration allows radiologists to confidently distinguish this benign entity from its malignant mimics. Implementation of a structured multimodality approach, anchored by mandatory radiographic or CT correlation, enables confident conservative management, reserving biopsy for rare or indeterminate cases and minimizing unnecessary procedural risk and oncologic referral.