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Background
Periscapular and scapular lesions are relatively uncommon and may be challenging to recognize. However, it is crucial to be able to identify characteristic imaging findings of these lesions, as they are often incidentally detected on imaging. Differentiating benign versus malignant entities in this anatomic region is necessary to recommend appropriate workup for suspicious findings or avoid unnecessary follow up for benign lesions.

Educational Goals / Teaching Points
The goal of this exhibit is to review the unique biomechanics of the scapula and scapulothoracic articulation with implications regarding overuse and activity-related conditions, describe the pathophysiology and differential of periscapular soft tissue lesions using cases from a quaternary multidisciplinary sarcoma center, and highlight the unique range of image-guided interventions (including injection, biopsy, and sclerotherapy and ablation).

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
This exhibit discusses the unique anatomy of the scapular region and the roles of radiograph, ultrasound (US), CT, MRI, and PET/CT on evaluating periscapular and scapular lesions. While the shoulder articulation often receives dedicated imaging and has been extensively studied and described, posterior chest wall lesions are uncommon, and the scapular and periscapular anatomy is often incidentally detected. The scapulothoracic articulation is comprised of muscle and bursa between the scapula and the thoracic wall. Specifically, three muscle layers comprise the articulation: superficial (trapezius, latissimus dorsi), intermediate (levator scapulae, rhomboids), and deep (serratus anterior, subscapularis). Two physiologic bursae within the scapulothoracic articulation function to reduce friction, including the infraserratus (scapulothoracic) bursa and the supraserratus (subscapularis) bursa. Overuse injuries can arise from disruption to the gliding motion, resulting in abnormal motion, pain, and crepitus, such as in scapulothoracic bursitis. Chest radiography is a fast and cheap modality that may allow visualization of osseous lesions calcifications. US is particularly useful for detecting superficial lesions and can guide biopsy. Cross-sectional imaging such as CT, MRI, and PET/CT are the main workhorse to evaluate periscapular lesions. While MRI lacks ionizing radiation and can better evaluate soft tissue, nerves, and vessels, CT is superior in visualizing osseous lesions. The majority of cases in our exhibit contain images from both modalities. PET/CT is useful particularly in evaluation of metastatic disease; however, false positives can arise from inflammation and infection, so care must be taken to avoid unnecessary workup for those lesions.

Conclusion
In closing, scapular and periscapular lesions are uncommon and often incidentally noted on imaging acquired for other purposes. After this educational exhibit, the participant should understand scapular and periscapular anatomy, characteristic scapular and periscapular lesions, and various imaging modalities and image-guided interventions that can be used for scapular and periscapular evaluation.