Suprasellar & trigeminal nerve oligodendroglioma with pseudoprogression after radiotherapy and serial MRI in a dog: a case report

Nicholas Rancilio ^1* Mary Drozd ² Logan Donaldson ³ Tyler Harm ¹ Keiko Murakami ¹

• ¹ Iowa State University, Ames, United States
• ² University of Nebraska-Lincoln, Lincoln, Nebraska, United States
• ³ VCA Midwest Veterinary Emergency & Referral Center, Omaha, United States

Pseudoprogression is a clinical and imaging phenomenon where there is progression in the size and contrast enhancement pattern of a glioma lesion following treatment with radiotherapy. In human beings there is a large body of literature describing the phenomenon of pseudoprogression in glioblastoma following radiotherapy. The occurrence of glioma in the cranial nerves has been reported in human beings as a clinically rare entity.A 7-year-old female spayed French Bulldog was presented for left sided craniofacial muscle atrophy of 3 months duration and episodes of compulsive circling to the left. After neurological examination an MRI of the brain was performed. A T2 and T2 FLAIR weighted hyperintense, non-contrast enhancing, T1 weighted hypointense intra-axial suprasellar lesion was found. Additionally, an extraaxial, T1 weighted hyperintense, and contrast enhancing mass was found at the level of the left trigeminal nerve. The lesions were presumptively diagnosed as glioma and left trigeminal nerve sheath tumor based on their imaging characteristics and the breed of the patient. A course of stereotactic radiotherapy was prescribed and 3 months after treatment there was significant progression in the size of the suprasellar mass indicative of either true progression or pseudoprogression. The left trigeminal nerve mass remained stable in size.Treatment with glucocorticoids resulted in regression in the size of the suprasellar mass based on magnetic resonance imaging 7 months after treatment. The left trigeminal nerve mass remained stable in size. Progression of the suprasellar mass and left trigeminal nerve mass occurred 9 months after the first course of treatment and a second course of stereotactic radiotherapy was administered.Sixteen months after the first course of radiotherapy a necropsy was performed. The suprasellar lesion and the left trigeminal nerve lesion were diagnosed as oligodendroglioma on histopathology.Trigeminal nerve oligodendroglioma as well as pseudoprogression following radiotherapy have not been described in the dog. Pseudoprogression following radiotherapy should be considered a differential diagnosis for progression of presumed or confirmed glioma lesions following treatment with radiotherapy. Concurrent oligodendroglioma lesions in the trigeminal nerve are also possible and should be considered in the list of differentials for dogs with concurrent brain lesions.