CASE REPORTS Clinical and MRI Findings in Three Dogs with Polycystic Meningiomas Fiona M. K. James, MSc, DVM, DVSc, DACVIM (Neurology), Ronaldo C. da Costa, PhD, DVM, DACVIM (Neurology)*, Amy Fauber, MS, DVM, DACVS, Andrew S. Peregrine, PhD, DVM, DEVPC, Beverly McEwen, PhD, DVM, DACVP, Joane M. Parent, DVM, MVetSc, DACVIM (Neurology) y , Robert Bergman, MS, DVM, DACVIM (Neurology) ABSTRACT One spayed female Labrador retriever and two castrated male golden retrievers were evaluated for chronic (i.e., ranging from 3 wk to 24 wk) neurologic signs localizable to the prosencephalon. Signs included seizures, circling, and behavior changes. MRI demonstrated extra-axial, contrast-enhancing, multiloculated, fluid-filled, cyst-like lesions with a mass effect, causing com- pression and displacement of brain parenchyma. Differential diagnoses included cystic neoplasm, abscess or other infectious cyst (e.g., alveolar hydatid cyst), or fluid-filled anomaly (e.g., arachnoid cyst). The cyst-like lesions were attached to the rostral falx cerebri in all cases. In addition, case 2 had a second polycystic mass at the caudal diencephalon. Surgical biopsy (case 3 with a single, rostral tumor via transfrontal craniectomy) and postmortem histology (in cases 1 and 2) confirmed polycystic meningiomas. Tumor types were transitional (cases 1 and 3) and fibrous (case 2), with positive immunohistochemical staining for vimentin. Case 3 was also positive for E-cadherin, s100, and CD34. In all cases, staining was predominantly negative for glial fibrillary acid protein and pancytokeratins, supporting a diagnosis of meningioma. This report describes the first cases of poly- cystic meningiomas in dogs. Polycystic meningiomas are a rare, but important, addition to the differential diagnoses for in- tracranial cyst-like lesions, significantly affecting planning for surgical resection and other therapeutic interventions. (J Am Anim Hosp Assoc 2012; 48:331–338. DOI 10.5326/JAAHA-MS-5774) Introduction Meningiomas are one of the most common primary intracranial tumors in dogs, and 33–49% of dogs with primary brain tumors have meningiomas. 1–3 Cystic meningiomas are a rare subtype of meningiomas, with few reports in the literature. 4–8 Although the prevalence of cystic meningiomas has not been established in dogs, between 2% and 4% of meningiomas in humans are cystic. 9 Polycystic meningiomas are reportedly even more rare in humans. 10,11 To the best of the authors’ knowledge, this report describes the first three cases of polycystic meningiomas docu- mented in dogs. Case Report Case 1 An 8 yr old spayed female Labrador retriever was referred to the Ontario Veterinary College Small Animal Clinic with a 1-mo history of behavior changes and increasing mental dullness. There was an initial increase in aggression toward people then a signifi- cant decrease in response to the owner and, increasingly, episodes of head-pressing, house-soiling, panting, pacing, circling to the right, and nightly vocalizations. The dog was receiving daily meloxicam a and glucosamine (brand unknown) for chronic de- generative disease of the hip and stifle joints. From the Department of Clinical Studies (F.J., R.C., J.P.), Department of Pathobiology (A.P.), and Animal Health Laboratory (B.M.), Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada; Department of Veterinary Clinical Sciences, Purdue University, West Lafayette, IN (A.F.); and Carolina Veterinary Specialists, Charlotte, NC (R.B.). Correspondence: jamesf@uoguelph.ca (F.J.) CSF cerebrospinal fluid; FLAIR fluid-attenuated inversion recovery; IHC im- munohistochemistry; T1WI T1-weighted images; T2WI T2-weighted images; TE time to echo; TR repetition time *R. da Costa’s present affiliation is Department of Veterinary Clinical Sciences, The Ohio State University, Columbus, OH. † J. Parent’s present affiliation is De ´ partement de Sciences Cliniques, Faculte ´ de Me ´ dicine Ve ´ te ´ rinaire, Universite ´ de Montre ´ al, St. Hyacinthe, Que ´ bec, Canada. ª 2012 by American Animal Hospital Association JAAHA.ORG 331