Relationship between magnetic resonance imaging findings and histological grade in spinal peripheral nerve sheath tumors in dogs

BACKGROUND: Peripheral nerve sheath tumors (PNSTs) are a group of neoplasms originating from Schwann cells or pluripotent cell of the neural crest. Therapeutic options and prognosis are influenced by their degree of malignancy and location. HYPOTHESIS/OBJECTIVES: Identify magnetic resonance imaging (MRI) features predictive of PNST histologic grade. ANIMALS: Forty‐four dogs with histopathological diagnosis of spinal PNSTs and previous MRI investigation. METHODS: A multicenter retrospective study including cases with (a) histopathologic diagnosis of PNST and (b) MRI studies available for review. Histologic slides were reviewed and graded by a board‐certified pathologist according to a modified French system (FNCLCC) for grading soft tissue sarcomas. The MRI studies were reviewed by 2 board‐certified radiologists blinded to the grade of the tumor and the final decision on the imaging characteristics was reached by consensus. Relationships between tumor grade and histological and MRI findings were assessed using statistical analysis. RESULTS: Forty‐four cases met inclusion criteria; 16 patients were PNSTs Grade 1 (low‐grade), 19 were PNSTs Grade 2 (medium‐grade), and 9 were PNSTs Grade 3 (high‐grade). Large volume (P = .03) and severe peripheral contrast enhancement (P = .04) were significantly associated with high tumor grade. Degree of muscle atrophy, heterogeneous signal and tumor growth into the vertebral canal were not associated with grade. CONCLUSIONS AND CLINICAL IMPORTANCE: Grade of malignancy was difficult to identify based on diagnostic imaging alone. However, some MRI features were predictive of high‐grade PNSTs including tumor size and peripheral contrast enhancement.