MRI and histopathology of primary extranodal spinal cord T-cell-rich B-cell lymphoma in a cat.

Case summary: A 7-year-old spayed female domestic shorthair cat was presented for evaluation of a 4-month history of slowly progressive back pain. Neurological and orthopaedic examinations revealed a low posture of the hindlimbs, reluctance to walk, a wide stance, hind limb ataxia and significant pain at the caudal spine, including the base of the tail. MRI of the brain and spinal cord demonstrated marked segmental dilation of the central canal with diffuse ependymal and parenchymal contrast enhancement, affecting almost the entire spinal cord. Widening of the intracranial ventricular system with a secondary mass effect on the surrounding cerebral parenchyma resulted in a reduction of cerebral cortex thickness as well as of the subarachnoid space, flattening of the cerebellum and a decreased size of the interthalamic adhesion. Histopathological examination of the brain and spinal cord revealed perivascular and parenchymal aggregates of mononuclear cells containing occasional atypical large lymphocytes, often infiltrating into blood vessels and the central canal, and affecting both white and grey matter. The most severe changes were found at the lumbosacral segment, with markedly distorted parenchyma and central canal, and the presence of neuronal and axonal degeneration and loss. Immunohistochemistry showed atypical large mononuclear cells positive to Pax5 (neoplastic B cells) and abundant small round cells positive to CD3 (reactive T cells), confirming the diagnosis of central nervous system T-cell-rich B-cell lymphoma with an angiocentric and angioinvasive distribution pattern. Relevance and novel information: This article describes imaging characteristics of a rare case of histopathologically confirmed central nervous system T-cell-rich B-cell lymphoma.