Case Report: Primary Diffuse Leptomeningeal Oligodendrogliomatosis in a Young Adult Cat

Abstract

A 2-year-old cat was presented with progressive ataxia. Despite treatment the animal died. Pathomorphological examination revealed a widespread leptomeningeal mass at all levels of the central nervous system accentuated on the cervical spinal cord and the medulla oblongata without presence of a primary intraaxial tumor. The neoplasm was mainly composed of round, uninucleate cells with hyperchromatic nuclei, which were immunopositive for OLIG2, doublecortin, MAP2, synaptophysin, and vimentin, indicating components of both oligodendroglial and neuronal differentiation. Ki-67 immunohistochemistry indicated a high proliferation activity of the neoplasm. Few GFAP positive and Iba-1 positive cells were interpreted as reactive astrocytes and macrophages or microglia, respectively. The tumor was immunonegative for CD3, CD20, PAX5, MUM1, pan-cytokeratin, S100, NSE, p75^NTR, NeuN and periaxin. These findings led to the diagnosis of primary diffuse leptomeningeal oligodendrogliomatosis. This is the first reported case of this entity in a young cat, which should be considered as a differential diagnosis for diffuse subarachnoidal round cell infiltrates.

Keywords: CNS; OLIG2; PDLG; feline; glioneuronal tumor; meninges; oligodendroglioma.

Figure 1

Cervical spinal cord, cat. (A) Transversal section of formalin-fixed spinal cord with leptomeningeal pale, gray-beige mass (dashed line: junction tumor-spinal medulla). (B) Diffuse, basophilic cell infiltrates and edema within leptomeninges with compression of spinal cord. Spinal nerves (asterisks) are omitted by the tumor. HE stain. (C) Neoplastic infiltrates with junction to spinal medulla (bottom right) and necrosis (asterisk), HE stain. Scale bar: 50 μm. (D) High mitotic activity within the neoplasm (arrows), HE stain. Scale bar: 20 μm.

Figure 2

Spinal cord, cat. Tumor cells are diffusely immunopositive for OLIG2 (A), doublecortin (B), and MAP2 (C). The majority of tumor cells stained positive with synaptophysin (D). Positive vimentin reaction is mainly restricted to tumor—associated vasculature (E). High proliferation activity was demonstrated with positive nuclear staining for Ki-67 (F). Scale bars: 50 μm.