Abstract：
Pilomatrixoma is a relatively rare benign skin appendageal tumor, often presenting in the pediatric age group as a nodular lesion and most commonly involving the head and neck, making it amenable to primary fine needle aspiration (FNA) diagnosis. We report the clinical and histopathological findings of two cases of pilomatrixoma in children, both of which were initially misdiagnosed as small round blue cell tumors due to high cellularity and misinterpretation of the proliferating basaloid cells. Histopathology revealed basal cell proliferation and mitoses indicating that they were progressive, early lesions. The first case showed membranous positivity for CD99 which prompted a diagnosis of Ewing sarcoma. Awareness of the morphological spectrum including positivity for CD99 and careful evaluation of cell block histology could have averted the misdiagnosis. Pilomatrixoma should be included as an important differential diagnosis when faced with primitive-appearing cells on FNA, especially in children with mass lesions in the head and neck region.
摘要：
Pilomatrixoma是一种相对罕见的良性皮肤阑尾肿瘤，在儿童年龄组中通常表现为结节性病变，最常见于头颈部，使其适合初级细针穿刺（FNA）诊断。我们报告了2例儿童毛囊结肠瘤的临床和组织病理学发现，由于高细胞性和对增殖的基底细胞的误解，两者最初都被误诊为小的圆形蓝色细胞肿瘤。组织病理学显示基底细胞增殖和有丝分裂表明它们是进行性的，早期病变。第一例显示CD99膜性阳性，提示诊断为尤文肉瘤。对包括CD99阳性在内的形态学光谱的认识以及对细胞块组织学的仔细评估可以避免误诊。当面对FNA上的原始出现细胞时，应将Pilomrayxoma作为重要的鉴别诊断。尤其是头颈部有肿块病变的儿童。
