Clinical, magnetic resonance imaging, and histopathologic features of a hypoglossal malignant peripheral nerve sheath tumor in a maltese dog

Malignant tumours arising from peripheral nerves or displaying differentiation along the lines of the various elements of the nerve sheath are collectively referred to as MPNSTs. Histologically, in human MPNST, the malignant nature of these tumours is associated with an infiltrative and cellular proliferation of atypical, mitotically active spindle cells. Their predilection for sites varies with the species. In dogs the most common site for MPNST is the nerve roots or nerves of the brachial plexus, while the cranial nerve more frequently involved is the trigeminal nerve. In humans, hypoglossal peripheral nerve sheath tumours are rare, only few cases are described in literature; and the malignant forms are even exceptional. Fifty per cent of cases displayed both an intra- and extracrania component, and are referred as dumbbell-shaped tumours. To our knowledge this is the first case report an hypoglossal MPNST in a dog. In our case the tumour was dumbbell-shaped, with both intra-and extracranial components and associated with characteristic clinical signs of hypoglossal tumour. The malignant histological appearance of the lesion occurred without infiltrative growth.