Case Report: Atypical magnetic resonance appearance of an organizing hematoma in the brain of a dog.

An 8-year-old German Short-haired Pointer was admitted with acute onset of blindness, behavioral abnormalities, and hemiparesis. Neurologic findings localized to the left forebrain. A well-demarcated, circular lesion with mixed signal intensity and mixed contrast enhancement was demonstrated with magnetic resonance (MR) imaging. There was marked mass effect with an irregularly marginated peripheral area of hyperintensity on T2-weighted and fluid-attenuated inversion recovery sequence images and areas of signal-void on gradient-echo sequencing. The distinctly circular appearance of this abnormality is atypical for most disease processes including intracranial hematoma found with MR imaging of the intracranial structures in dogs. Differential diagnosis included primary hemorrhage, neoplasia, inflammatory disease, as well as uncommon diseases such as parasite migration. The dog was euthanized per the owner's request immediately following the MR. Pathologically, there was an organizing hematoma, characterized by centrally located fibrous tissue surrounded by an area of hyperacute hemorrhage extending into the adjacent neuroparenchyma in the thalamus. The imaging features of this intracerebral hemorrhage were similar to previous reports but also contained unique features including a geometrically circular border, a lack of peripheral hypointensity on T1-weighted images, and central contrast-enhancement. As this was a histologically confirmed hematoma, the imaging features in this case should be included within the spectrum of potential imaging abnormalities associated with intracranial hematomas in dogs.