Malignant oligoastrocytoma in the spinal cord of a cat

Abstract

A 12-year and 3-month spayed female mixed cat was presented with severe lumbar pain. Magnetic resonance imaging and postmortem examination revealed a swollen lesion in the spinal cord at L3 level. Histologic examination identified extensive neoplastic cell proliferation with massive necrosis in the tumor tissue. Two types of neoplastic cells were recognized. One type of neoplastic cells were large cells characterized by round to polygonal shape and abundant eosinophilic cytoplasm (referred to as "large cells"). The other neoplastic cells were small, densely proliferated, and had round to irregular shape and scant eosinophilic cytoplasm (referred to as "small cells"). Both types of cells were positive for oligodendrocyte transcription factor 2 and SRY-box transcription factor 10. Glial fibrillary acidic protein was positive in large cells but negative in most small cells. Digital analysis for Ki-67-stained tumor tissues found that total 21.1% ± 6.5% of tumor cells were positive for Ki-67. Based on these findings, we diagnosed malignant oligoastrocytoma in the spinal cord.

Keywords: Ki-67; cat; oligoastrocytoma; spinal cord; tumor.

Fig. 1.

MRI and gross images of the lumbar spinal cord. (A) T1-weighed MRI planes of the spinal cord following contrast administration. Arrow heads indicate the mass lesion. Left: coronal. Middle: sagittal. Right: axial. (B) Gross images of dorsal (left) and ventral (right) side of the spinal cord. Arrows indicate the swollen lesion. Bars=1 cm. R=right, L=left, Cr=cranial, Ca=caudal.

Fig. 2.

Hematoxylin and eosin staining of the mass in the lumbar spinal cord. (A) The subgross image of the lumbar spinal cord. The asterisk indicates the necrotic area. (B–D) High magnification of the tumor tissues. Insets show large cells (B) and small cells (C). Arrows in D indicate newly formed blood vessels. D=dorsal, V=ventral, R=right, L=left. Scale bars=1 mm (A), 20 µm (B–D).

Fig. 3.

Immunohistochemistry of the mass in the lumbar spinal cord. (A–F) Representative images (A, C, E) and signal intensities (B, D, F) of oligodendrocyte transcription factor 2 (OLIG2), SRY-box transcription factor 10 (SOX10) and glial fibrillary acidic protein (GFAP) staining. (G) Representative images of Ki-67. (H and I) Ki-67 expression profiles in all tumor cells (H) and in each tumor cell type (I). The graphs were created based on the average percentages ± SD. Large=large cells, Small=small cells. Bars=20 µm.