Dermoscopic findings in two cases of trichogerminoma.

Trichogerminoma (TG) is a rare, benign, cutaneous adnexal tumor originating from the hair germ epithelium. It typically presents as an asymptomatic, slowly enlarging nodule predominantly on the head, face, or trunk. Despite its benign nature, precise diagnosis is crucial because of its potential to become malignant. There has been no previous report on the dermoscopic findings of TG. In this study, we reviewed the dermoscopic findings of two cases in detail and contrasted them with the pathological findings. In the first case, an 80-year-old male presented with a forehead nodule that was initially suspected to be basal cell carcinoma (BCC). Dermoscopic examination revealed arborizing vessels, milia-like cysts, and comedo-like openings. Histological examination supported a diagnosis of TG, showing basaloid cell nests with peripheral palisading and pathognomonic "cell balls." The second case involved a 50-year-old female with a nodular lesion on her scalp. Dermoscopy showed arborizing vessels, milia-like cysts, and blue-gray ovoid nests. Based on the presence of "cell balls" observed in histopathological examination, this case was also diagnosed as TG. This report is seminal in documenting the specific dermoscopic patterns associated with TG, notably the presence of arborizing vessels in conjunction with features indicative of adnexal differentiation, such as milia-like cysts and comedo-like openings. Although differentiating TG from other follicular tumors such as BCC and trichoblastoma based solely on dermoscopy is challenging, these features suggest follicular differentiation in TG. This report contributes uniquely to the existing data on TG, enhancing our understanding of this rare tumor and how to diagnose it.