Four cases of a rare melanotic variant of malignant nerve sheath tumour (MNST) in dogs are described. All four cases presented with neurological clinical signs due to multicentric, intradural, intra- and extraparenchymal neoplasms that surrounded the spinal and cranial nerves and infiltrated the adjacent spinal cord and brain. The dogs were young (3 months to 3 years of age), all were female and four different breeds were represented. Characteristic histological features were interweaving fascicles of spindle-shaped cells, sometimes with an architecture reminiscent of Antoni A and B patterns. Some spindle cells showed prominent cytoplasmic melanin pigmentation and such cells were positive by Masson-Fontana stain. Immunohistochemistry performed in three cases was positive for S100 and vimentin, strongly positive for melan A in the melanized cells and negative for glial fibrillary acidic protein and periaxin. Non-melanized cells did not express melan A. Transmission electron microscopy findings in one case were consistent with a peripheral nerve sheath tumour and demonstrated cytoplasmic pre-melanosomes and melanosomes. Melanotic variants of MNSTs are rare in animals with only a solitary report of two previous canine cases in the literature.

描述了四例狗恶性神经鞘瘤（MNST）的罕见黑色素变体。由于多中心，硬膜内，实质内和实质外的肿瘤围绕着脊髓和颅神经并浸润到邻近的脊髓和大脑，所有这四个病例均表现出神经系统的临床症状。这些狗是年轻的（3个月至3岁），都是雌性，代表了四个不同的品种。典型的组织学特征是纺锤形细胞的纤维束交织在一起，有时具有让人联想到安东尼A和B模式的结构。一些纺锤体细胞显示出明显的胞质黑色素色素沉着，并且这些细胞通过Masson-Fontana染色呈阳性。3例患者的免疫组织化学检查显示S100和波形蛋白为阳性，黑色素细胞中黑色素A呈强阳性，神经胶质原纤维酸性蛋白和过氧化物酶阴性。非黑色素细胞不表达黑色素A。在1例中的透射电子显微镜检查结果与周围神经鞘瘤一致，并显示出胞质前黑素体和黑素体。MNSTs的黑色素变体在动物中很少见，文献中仅有两个以前的犬类病例的报道。