A 9-year-old male mixed breed cat showed chronic progressive neurological symptoms, which are represented by ataxia and seizures. At necropsy, spinal roots and spinal ganglions at the level of sixth cervical nerve to second thoracic nerve were bilaterally swollen and replaced by white mass lesions. Right brachial plexus and cranial nerves (III, V and VII) were also swollen. A mass lesion was found in the right frontal lobe of the cerebrum. Histologically, neoplastic lymphocytes extensively involved the peripheral nerves, and they infiltrated into the cerebral and spinal parenchyma according to the peripheral nerve tract. Immunohistochemically, most neoplastic lymphocytes were positive for CD20. The clinical and histological features in this case resemble those of neurolymphomatosis in humans.

BACKGROUND Arteriovenous malformation (AVM) of the trigeminal nerve root (TNR) is a rare subtype of the lateral pontine AVM. Most of them are diagnosed when they bleed or exert trigeminal neuralgia. Venous congestive edema is a rare phenomenon caused by TNR AVMs. OBSERVATIONS An 82-year-old man was admitted with progressive limb weakness and dysphasia. Magnetic resonance imaging (MRI) revealed extensive edema of the medulla oblongata and the upper cervical cord with signal flow void at the C3 anterior spinal cord. Vertebral angiography revealed a small nidus fed mainly by the pontine perforating arteries (PPAs). The anterior pontomesencephalic vein (AMPV) was dilated, functioning as the main drainage route. This suggests that venous hypertension triggered the brainstem and upper cervical cord edema. MRI with gadolinium enhancement showed that the nidus was located around the right TNR. Because the nidus sat extrinsically on the pial surface of the right TNR’s base, microsurgical obliteration with minimum parenchymal injury was achieved. Postoperative MRI showed disappearance of the brainstem and cervical cord edema with improved clinical symptoms. LESSONS TNR AVM is rarely associated with brainstem and upper cervical cord edema caused by venous hypertension of the congestive drainage system.