A clinical and radiological study on 31 palmoplanar epidermal cysts

Background: Epidermal cysts seldom arise on the palm or sole because of the absence of pilosebaceous apparatus in palmoplantar skin. Palmoplantar epidermal cysts (PPECs) are not included in this location's tumor category, because they appear as slightly elevated, hardly movable dermal or subcutaneous nodules without a central punctum, unlike other epidermal cysts. As a result, PPECs often mimic corns, calluses, or verruca. Objective: The purpose of this study was to review the clinical features of PPECs and to explore the usefulness of ultrasonography as a diagnostic tool. Methods: We retrospectively reviewed the medical records and ultrasonographic findings of 31 patients with PPECs among 341 patients with a confirmed epidermal cyst. Among them, 12 patients were evaluated preoperatively by ultrasonography. The data were compared between the ultrasonographic diagnosis and the final diagnosis. Results: Unlike previous reports, PPECs were relatively common, and comprised 9.1% (31/341) of all epidermal cysts. They also appeared more on the sole than on the palm. In addition, PPECs were confused with corns, calluses, and other benign tumors at the first visit, because of their different clinical features from ordinary epidermal cysts. However, preoperative ultrasonography of 12 cases enabled us to make a correct diagnosis. After the operation, no recurrence was found at the last follow-up in any of the patients. Conclusion: PPECs have some different clinical features compared to typical epidermal cysts with a nonpalmoplantar location. Therefore, it is often difficult to distinguish PPECs from other benign tumorous conditions. However, ultrasonography was useful for the preoperative diagnosis of PPECs because of its safety, low cost, non-invasiveness and, most importantly, its accuracy.