Metastatic Multifocal Malignant Peripheral Nerve Sheath Tumour in the Cervicothoracic Spinal Cord of a Dog Initially Mimicking Meningomyelitis Neurogenic Tumors and Paragangliomas Ento Key Malignant melanotic nerve sheath tumors in the spinal canal of psammomatous and non psammomatous type: Two case reports Malignant Peripheral Nerve Sheath Tumor of The Orbital Region Arising from Pre Existing Benign Neurofibroma in An Adolescent Patient of Neurofibromatosis Type 1: A Case Report and Review of Literature European Journal