一只五岁的男性英国斗牛犬患有左侧腹部一个直径为1cm，质地坚实、完整圆形的皮肤肿块。采集皮肤针刺吸引（FNA）活检样本进行细胞学分析。细胞学显示高度细胞密集的样本，由纺锤细胞、大量束状厚玻璃样嗜酸性物质（透明化胶原）和炎症细胞组成。纺锤细胞呈现中度异形性和核异位现象，椭圆形核具有颗粒状染色质，1-3个突出的圆形核仁，适量的纤细浆液质。细胞有时与嗜酸性细胞外基质相关。常见到双核和三核的纺锤细胞。也存在数量不多的巨噬细胞、小淋巴细胞和孤立的颗粒丰富的肥大细胞。肿块被切除并送检进行组织病理学检查，在深皮肤和皮下组织中发现一个有限界限、无包膜的肿块，由透明化的胶原纤维和间以纺锤状间质细胞相隔的组织构成。具有轻度核异形性和核异位现象，每个高倍视野10个视野中的有不足一次有丝分裂。肿块已完全切除。发现与一种罕见的良性纤维瘤变体——疤痕瘤一致。肿瘤细胞对波形蛋白表现阳性免疫反应，少至中度数量的瘤细胞对α-平滑肌肌动蛋白表现阳性免疫反应。这是与组织病理学和免疫标记相关的疤痕瘤的首次细胞学描述。在疑似疤痕瘤的情况下，由于细胞学检查中可能出现中度细胞异型性，将其与疤痕纤维肉瘤区分开来，有必要进行组织病理学检查。© 2023美国兽医临床病理学会。

A five-year-old male English Bulldog was presented with a firm, well-circumscribed, 1 cm in diameter cutaneous mass on the left flank. Fine-needle aspiration (FNA) biopsy samples were collected for cytologic analysis. Cytology revealed a highly cellular sample consisting of spindle cells, numerous bundles of thick, glassy eosinophilic material (hyalinized collagen), and inflammatory cells. Spindle cells showed moderate anisocytosis and anisokaryosis, had oval nuclei with coarsely stippled chromatin, 1-3 prominent round nucleoli, and moderate amounts of wispy cytoplasm. Cells were occasionally associated with an eosinophilic extracellular matrix. Binucleated and trinucleated spindle cells were often noted. Low numbers of macrophages, small lymphocytes, and individual well-granulated mast cells were also present. The lesion was excised and submitted for histopathologic examination, revealing a well-delineated, nonencapsulated mass composed of hyalinized collagen fibers separated by spindle-shaped mesenchymal cells in the deep dermis and subcutis. Mild anisocytosis and anisokaryosis and less than one mitosis per 10 × high power fields were present. Excision of the mass was complete. The findings were consistent with a keloidal fibroma, a rare benign variant of fibroma. Neoplastic cells showed positive immunoreactivity for vimentin, and a small-to-moderate number of tumor cells showed positive immunoreactivity for α-smooth muscle actin. This is the first cytologic description of a keloidal fibroma correlated with histopathologic findings and immunolabeling. In cases where keloidal neoplasia is suspected, and since moderate cellular atypia can be present on cytologic examination even in cases of keloidal fibroma, histopathologic examination is necessary to differentiate between keloidal fibroma and keloidal fibrosarcoma.© 2023 American Society for Veterinary Clinical Pathology.