Received: 5 February 2017 Revised: 18 April 2017 Accepted: 24 April 2017 DOI: 10.1111/vru.12535 ORIGINAL INVESTIGATION Clinical and imaging findings, treatments, and outcomes in 27 dogs with imaging diagnosed trigeminal nerve sheath tumors: A multi-center study Katie E. Swift 1 Stephanie McGrath 2 Michael W. Nolan 3 ∗ Martin Young 4 Michael Reese 5 Sangeeta Rao 2 Elissa Randall 1 Del Leary 1 Susan LaRue 1 ∗ 1 Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO 80523 2 Department of Clinical Sciences, Colorado State University, Fort Collins, CO 80523 3 Department of Clinical Sciences and Compar- ative Medicine Institute, North Carolina State University, Raleigh, NC 27607 4 Bush Veterinary Neurology Service, Richmond, VA 23230 5 Department of Veterinary Clinical Sciences, Purdue University, West Lafayette, IN 47907 Correspondence Michael W. Nolan, Department of Clinical Sci- ences, and Comparative Medicine Institute, North Carolina State University, Raleigh, NC 27607. Email: mwnolan@ncsu.edu Abstract The clinical behavior of canine trigeminal nerve sheath tumors and benefits of previously reported treatments are incompletely defined. Aims of this retrospective, multicenter, observational study were to describe clinical signs, tumor localization characteristics, treatments, and clinical out- comes in a group of dogs with this neoplasm. Databases at four hospitals were reviewed for dogs with a trigeminal nerve sheath tumor diagnosis, magnetic resonance imaging (MRI) studies, and presentation between 2004 and 2014. A single observer recorded medical record findings and two observers recorded MRI characteristics by consensus. A total of 27 dogs met inclusion criteria (15 treated with stereotactic radiation therapy and 12 unirradiated). Two unirradiated dogs were excluded from outcome analyses. The most common presenting signs were masticatory muscle atrophy (26 dogs), neurologic signs referable to intracranial disease (13), and ocular disease (12). Based on MRI findings, all dogs had disease extending centrally at the level of the brainstem. The most commonly affected trigeminal nerve branches were the mandibular (26 dogs), maxillary (22), and ophthalmic (10). Of 15 dogs treated with stereotactic radiation therapy, one had improved muscle atrophy, and six had poor ocular health after treatment. Neurologic signs improved in 4/5 dogs with intracranial signs. Overall median survival time for the 10 unirradiated dogs with available follow-up was 12 days and 441 days for the 15 stereotactic radiation therapy dogs. Mean survival times between these groups were not significantly different (mean 95% CI for unirradi- ated dogs was 44–424 days and mean 95% CI for stereotactic radiation therapy dogs was 260– 518 days). KEYWORDS neurooncology, radiation oncology, small animal oncology, stereotactic radiation therapy 1 INTRODUCTION In the dog, centrally located nerve sheath tumors can arise from spinal nerves, cranial nerves, or nerve roots. They have been reported to arise from Schwann cells or perineural fibroblasts and commonly occur in the caudal cervical region of the spinal cord. 1,2 The most commonly affected cranial nerve in the dog is the trigeminal nerve. 3 Reported clinical signs in dogs with trigeminal nerve sheath tumors include uni- lateral masticatory muscle atrophy, reduced facial sensation, dimin- ished palpebral reflex, and reduced corneal sensation. 1,4 Neurologic signs associated with brainstem compression can also occur. 4,5 Dif- ∗ These senior authors contributed equally to this work. Michael Reese’s current address is Southeast Veterinary Neurology, Miami, FL 33165. ferential diagnoses include infectious and inflammatory neuropathies; lymphoma has also been reported to affect the trigeminal nerve. 6 Malignant nerve sheath tumors are classified as soft tissue sarcomas, and in general are thought to have relatively low metastatic potential. 3 To the authors’ knowledge, such data have not been reported specifi- cally in canine trigeminal nerve sheath tumors. Magnetic resonance imaging (MRI) is an established imaging modal- ity upon which a presumptive diagnosis of trigeminal nerve sheath tumor can be made. 3 Previously reported are outcomes of dogs with no treatment, surgical removal, and more recently, stereotactic radio- therapy or radiosurgery. 4,7–9 Untreated dogs with presumptively diag- nosed trigeminal nerve sheath tumors have been reported to have a median survival time of 12 months; whereas two dogs treated with surgery survived 4 and 27 months, respectively. 4 The published Vet Radiol Ultrasound. 2017;58:679–689. c  2017 American College of Veterinary Radiology 679 wileyonlinelibrary.com/journal/vru