Back to the Basics: When Radiographs Solve the Case.

Myositis ossificans circumscripta is a benign, self-limiting heterotopic ossification usually occurring after a traumatic event. Our case describes a rare etiology given the occurrence after vaccination in a child. Indeed, to date, only two cases of myositis ossificans circumscripta after COVID-19 vaccination have been reported, both in adults. In this first pediatric case, radiographs performed at appropriate time allowed for a conclusive tissue characterization and hence diagnosis. CT and MR scans performed early after clinical manifestation showed only progressive, severe edema of the soft tissue of the shoulder while the later acquired radiograph and radiographic follow-up demonstrated the heterotopic ossification in the deltoid. Rapid soft tissue swelling and edema, in correlation with a potential local traumatic event, even if atypical, should raise suspicion of myositis ossificans circumscripta. With proper timing (at least 10 days after the trigger), radiographs can be crucial in showing the typical ossification pattern. · Myositis ossificans circumscripta may have various etiologies including vaccinations.. · The rapid onset and temporal correlation of clinical symptoms and imaging findings are essential to guide toward the correct diagnosis.. · MR is very sensitive to the inflammatory process accompanying myositis ossificans circumscripta but the edema may hamper the characterization of the peripheral calcific areas.. · Radiographs can be decisive for the diagnosis of myositis ossificans circumscripta and are useful to monitor the progressive shrinking of the ossification..