Preoperative Diagnostic Accuracy and Clinicopathological Characteristics of Pilomatricoma: A Single-Institution Study of 51 Patients.

Pilomatricoma is a benign adnexal tumor derived from hair matrix cells and commonly affects pediatric populations. Despite its relatively characteristic clinical presentation, presurgical diagnostic accuracy remains low in many reports. This retrospective study analyzed 55 lesions from 51 Japanese patients with histopathologically confirmed pilomatricoma treated at Toyama University Hospital between 2006 and 2024. Clinical information, including age, sex, lesion location and characteristics, and the initial clinical diagnosis, was extracted from medical records. Diagnostic accuracy was defined as concordance between the clinical diagnosis and the final pathological diagnosis. Univariate and multivariate analyses were performed to examine factors associated with a correct initial diagnosis. A Spearman's correlation analysis was also conducted to evaluate the relationship between the duration from symptom awareness to surgical excision and the basophilic-to-shadow cell (B/S) ratio. The overall diagnostic accuracy was 21 out of 55 cases (38.2%). Patients in the correctly diagnosed group (n = 21) were significantly younger than those in the incorrectly diagnosed group (n = 34) (median: 17 vs. 36 years, p = 0.002) and had a longer interval from symptom awareness to the initial visit (median: 300 vs. 113.5 days, p = 0.03). Bluish coloration was significantly associated with correct diagnosis (14/21, 66.7%; p = 0.005), while reddish coloration was more commonly observed among misdiagnosed cases (18/34, 52.9%; p = 0.04). The multivariate analysis did not identify any independent predictors of diagnostic accuracy. A moderate negative correlation was observed between the B/S ratio and time to surgery (ρ = -0.40, p = 0.002), consistent with the histological progression of the tumor over time. These findings underscore the complexity of clinical diagnosis and highlight the importance of routinely considering pilomatricoma in the differential diagnosis of cutaneous nodules, regardless of patient age or other clinical features. Further studies are warranted to improve early recognition of this frequently misdiagnosed tumor.