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E1819. It's Not a Tumor: Pseudolesions of the Foot and Ankle
Authors
  1. Jordan Davis; SAUSHEC
  2. Peter Williams; SAUSHEC
  3. Douglas Byerly; SAUSHEC; Uniformed Services University of Health Sciences
  4. Nathan Cecava; SAUSHEC; Uniformed Services University of Health Sciences
Background
Foot and ankle pain have a high prevalence in the United States population, with as many as 24% of adults over the age of 45 endorsing frequent foot pain and 15% endorsing frequent ankle pain. Frequently, imaging is included in the clinical workup, especially in the setting of a palpable mass. The overall incidence of pseudolesions and benign lesions is much higher than that of malignant soft tissue tumors in the foot and ankle. Therefore, it is important for the radiologist to understand the relative incidence and appearance of foot and ankle pseudolesions to arrive at a reasonable differential diagnosis and appropriate recommendation to spare the patient unnecessary advanced imaging, tissue sampling, or surgery. There are a multitude of benign processes which may result in a pseudolesion in the foot or ankle. Many have distinct imaging features, such as ganglion cysts, accessory muscles, muscle herniations, post-traumatic hematomas, myositis ossificans, osteomyelitis, synovial chondromatosis, tumoral calcinosis, crystal deposition disease, tenosynovial giant cell tumor, pseudoaneurysm and other vascular processes, and inflammatory processes such as tenosynovitis.

Educational Goals / Teaching Points
Discuss and provide examples of basic anatomy and normal imaging appearance of the foot and ankle. Review the various foot and ankle pseudolesion types and their prevalence. Review clinical history and physical examination findings which may aid a radiologist in pseudolesion evaluation. Provide real case examples of several pseudolesions and emphasize pertinent imaging findings in multiple imaging modalities. Discuss potential pitfalls in the diagnosis of benign pseudolesions and discuss strategies to avoid mischaracterization which may lead to unnecessary tests or treatments.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
We will discuss anatomy, disease processes, injuries and normal variants which can result in foot and ankle pseudolesions. We will highlight clinical clues as well as the strengths and limitations of radiography, ultrasound and magnetic resonance imaging (MRI) in pseudolesion evalution. Pathophysiology and presentation of various pseudolesion disease processes such as inflammatory arthropathy or crystalline deposition disease will be reviewed.

Conclusion
The foot and ankle contain complex osseous and soft tissue anatomy, and when presented with a mass, it may be difficult to determine the structure of origin and distinguish between benign and malignant processes. The radiologist plays a key role in this endeavour and must ensure that the relatively few cases of malignant disease are promptly identified and further evaluated with core needle or excisional biopsy. However, most masses in the foot and ankle will be benign lesions or pseudolesions. Armed with knowledge of common foot and ankle pseudolesions, the radiologist can play a key role in prompt and accurate diagnosis for these patients and thereby prevent unnecessary work-up and invasive procedures.