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E1694. Which Is Which? A Primer for New Trainees to Differentiate Two Confusing Osseous Pathologies
Authors
  1. Abtin Jafroodifar; SUNY Upstate Medical University
  2. Sahir Quraeshi; SUNY Upstate Medical University
  3. Zaid Siddique; SUNY Upstate Medical University
  4. Marlon Coelho; SUNY Upstate Medical University
  5. Atin Goel; SUNY Upstate Medical University
  6. Ryan Thibodeau; SUNY Upstate Medical University
  7. Mujtaba Mohammed; SUNY Upstate Medical University
Background
Identifying and diagnosing skeletal lesions are often one of the most difficult situations new trainees encounter due to the vast number of different entities and their similar overlapping radiographic findings. Parosteal osteosarcoma(POS) and osteochondroma(OC) are particularly notorious mimickers of each other. Not only are they radiographically similar lesions, they require vastly different treatment and management goals. The purpose of this exhibit is to present POS and OC using patient cases from our institution to highlight the unique radiological findings of these two entities in order to easily distinguish them from each other. Moreover, we aim to give new trainees the tools to properly identify these lesions in a timely manner, as a delay in diagnosis may change the course of treatment and management[5].

Educational Goals / Teaching Points
POS and OC are radiographically similar lesions which tend to be confused by new trainees. This educational exhibit will set forth to shed light on the most confusing aspects of these two disease processes. First, POS and OC will be introduced using respective patient cases from our institution. Then the relevant etiology, presentation, differential diagnosis, management, anatomy, histology, and pathogenesis of these two entitled will be reviewed in a table format to facilitate easy comparison. Furthermore, we will compare and contrast the radiological findings of POS and OC using imaging from our institution. Lastly, we will illustrate an easy-to-use algorithm for differentiating these two lesions using a multimodality approach.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
POS is a malignant primary bone tumor that arises from the outer fibrous layer of periosteum; it also happens to be the most common type of juxtacortical osteosarcoma[1]. In contrast, OC is a benign “tumor-like” lesion of the bone, which is more commonly accepted as a developmental lesion[2]. These two lesions demonstrate varying overlap in radiological findings, such as both presenting as exophytic lobulated osseous masses on plain radiograph. However, there are key differences that a trainee should be aware of in order to properly identify the correct disease. This includes the presence of underlying corticomedullary continuity and a smooth cartilaginous cap, which is often pathognomonic for OC[3], but not always[4]. Alternatively, the identification of a cleavage plane at the junction of the osseous mass and parent bone is more suggestive of a POS[1]. This educational exhibit will highlight the differences in these two entities using relevant imaging findings pertaining to each pathology.

Conclusion
New radiology trainees often have a difficult time in differentiating POS and OC due to their radiological similarities. The knowledge of the typical imaging patterns of each entity proves important in order to make a timely diagnosis; also, misleading features are just as important to be aware of. This educational exhibit will aim to review the most important factors when assessing for POS and OC in order to allow new trainees to comfortably, and confidently, make a reasonable diagnosis via a multimodal imaging algorithm.