History

A 3.2-kg neutered male Persian cat that was 13 years and 9 months old was referred to the San Marco private veterinary clinic because of acute onset of difficulties walking on the hind limbs, reluctance to jump, and urination and defecation in inappropriate places. According to the owner, the described signs appeared to be gradually and slowly worsening over the last 2 weeks prior to presentation. The cat lived indoors, was fed with a commercial diet, and was not regularly vaccinated.

Clinical and Gross Findings

Physical examination was within normal limits. Neurological examination revealed paraparesis, proprioceptive ataxia on the hind limbs, and hyperalgesia at palpation of the thoracolumbar spine. The remaining neurological examination was unremarkable. According to neurological examination, a thoracolumbar (T3-L3 segments) myelopathy was indicated. Based on signalment, onset of clinical signs, and clinical and neurological findings, a neoplastic lesion was first considered. However, inflammatory and infectious diseases (eg, discospondylitis with empyema, toxoplasmosis, feline infectious peritonitis), inflammatory noninfectious diseases (eg, meningomyelitis of unknown origin), and degenerative disorders (eg, intervertebral disk extrusion) could not be ruled out. Extensive clinicopathological evaluation, including complete cell blood count, serum biochemistry panel, coagulative profile, electrophoresis of serum proteins, and urinalysis, showed increased serum creatinine (2.53 mg/dL; normal range, 1.26 to 1.91 mg/dL) and decreased urine osmolality (998 mOsm/Kg; normal range, 1,340 to 2,254 mOsm/Kg). These findings were suggestive of chronic renal disease. Serum FIV and FeLV tests were negative.

Thoracic radiographs were within normal limits. Abdominal ultrasound showed mild splenomegaly, diffuse hepatopathy, and renal changes consistent with chronic kidney disease, including bilaterally reduced corticomedullary distinction and mild cortical hyperechogenicity. Ultrasound-guided fine-needle aspiration of spleen and liver were performed, and cytology revealed splenic extramedullary hematopoiesis and nonspecific hepatocellular degeneration respectively, without sign of neoplastic alterations.

A 3-T MRI (Skyra; Siemens) of the thoracolumbar spinal cord was performed. At the level of the seventh thoracic vertebra, the MRI showed a right paramedian ovoid intramedullary lesion measuring 7 mm in length, 5 mm in height, and 4 mm in width. The lesion appeared inhomogeneously hyperintense in T2-weighted and STIR sequences, appeared mildly hypointense in T1-weighted images, and showed a marked contrast enhancement.

Cerebrospinal fluid was collected from the lumbosacral cistern. Cerebrospinal fluid analysis revealed moderate pleocytosis (20 nucleated cells/mL) with a mixed cellular population characterized by a prevalence of monocytoid cells and a smaller percentage of hypersegmented neutrophilic granulocytes and lymphocytes.

Serum IgG and IgM antibodies and CSF real-time PCR for Toxoplasma gondii yielded a negative result.

A surgical biopsy of the identified lesion was proposed, but the owner declined it.

A corticosteroid therapy was started using an anti-inflammatory dosage (prednisolone 1 mg/kg administered orally every 24h). Despite an initial mild improvement of gait, the clinical condition continued to gradually worsen. After 1 month, the cat showed a scarcely ambulatory paraparesis, and considering the difficult management at home and the reserved prognosis, the owner elected for euthanasia.

Necroscopy and Histopathologic Findings:

At necroscopic examination, a 15-mm-long intraspinal oval, well-demarcated discoloration was present at the level of the T7 to T9 vertebral bodies (Figure 1).

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Photograph of the opened thoracic spinal canal showing a focal lesion on the spinal cord of a neutered male Persian cat that was 13 years and 9 months old. The cat was referred because of acute onset of difficulties walking on the hind limbs. The lesion appears as an oval, discolored bulge extending from the T7 to T9 vertebral bodies.

Citation: Journal of the American Veterinary Medical Association 261, 7; 10.2460/javma.22.12.0564

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Histopathology of the spinal cord revealed a poorly demarcated, unencapsulated, highly cellular centromedullary neoplastic mass with expansile growth that compressed the adjacent neuropil. The neoplasm was composed of 2 different cell populations: the first was characterized by large, polygonal cells with abundant eosinophilic homogeneous cytoplasm; nuclei were oval to round, large, and frequently placed peripherally, with coarse chromatin and visible magenta nucleoli (astrocytes and gemistocytes). Anisocytosis and anisokaryosis were severe with occasional mitotic figures. The second population was characterized by discrete smaller round cells, with a high nucleus-to-cytoplasm ratio, small amount of cytoplasm, and round central nuclei with finely stippled chromatin and without prominent nucleoli. Anisocytosis and anisokaryosis were mild, and mitosis was rare (Figure 2). Multifocal to coalescing areas of lytic necrosis were also present.

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Photomicrographs of the spinal lesion from the cat in Figure 1. A and B—The neoplasm shows a mixed cell population composed of markedly atypical astrocytes with anisokaryosis and large nucleoli (arrowheads) and multiple infiltrating oligodendrocytes (arrows). H&E stain; bar = 200 µm.

Citation: Journal of the American Veterinary Medical Association 261, 7; 10.2460/javma.22.12.0564

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Immunohistochemistry showed diffuse cytoplasmic glial fibrillary acidic protein positivity in large polygonal cells, while nuclei of the other population are diffusely positive for Olig-2.

Morphologic Diagnosis and Case Summary

The cat of the described case suffered from spinal cord anaplastic oligoastrocytoma, highly infiltrative and poorly proliferative, corresponding to WHO grade III.¹

Comments

Gliomas are neuroepithelial tumors usually classified based on the histologic type and malignancy grade.¹ Concerning the histologic type, gliomas are principally distinguished in oligodendrogliomas, astrocytomas, and undefined gliomas.¹ Oligoastrocytomas are characterized by the simultaneous finding of both astrocyte and oligodendrocyte neoplastic populations at the histopathological evaluation.¹ Based on the grade of cellular differentiation, these neoplasms are further classified as low and high grade.¹

In veterinary medicine, there are only a few reports describing feline spinal gliomas. A retrospective study² aiming to determine the prevalence of feline spinal tumors reported glial neoplasia in only 8 out of 85 cats included in the study. In particular, feline spinal cord oligoastrocytomas were described in 2 out of 7 cats included in a case series³ illustrating clinicopathologic features of feline spinal cord gliomas. In both cats, neurological signs indicated a cervicothoracic localization confirmed by both MRI and necroscopic findings.³ A recent case report describes a malignant oligoastrocytoma located in the lumbar spinal cord of a cat presented for lumbar pain that progressed to paraplegia and loss of deep pain perception over a period of 1 month.⁴ Similarly, in the present case, neurological signs were suggestive of a thoracolumbar myelopathy with a subtle onset and a rapid worsening. MRI was used to confirm the main suspicion of a neoplastic lesion and exclude other differentials. MRI allows the determination of a more precise lesion localization in relation to the dura mater as extradural, intradural-extramedullary, or intramedullary. This distinction is fundamental in the case of suspected neoplastic lesions to formulate a list of possible differential diagnoses in the alive patient and plan a proper treatment protocol.³

Histopathology and immunohistochemistry techniques provide a definitive neoplasm diagnosis, evaluate distinction of the neoplasm from normal tissue, and determine the grade of cell differentiation and rate of tumor growth.⁵ In the present report, staining for glial fibrillary acidic protein and Olig-2 allowed a better distinction of the 2 populations of cells composing the tumor, without having apparent doubts about their cellular progenitors.

Unfortunately, biopsies of spinal lesions are only rarely performed, often due to the owner’s reluctance to permit surgical treatment and considering the high risk of complications. In the cat described in this report, a palliative medical therapy was started based on MRI findings, according to what was previously reported in the veterinary literature. Euthanasia was elected due to the progression of neurological signs, considering the worse prognosis.

In summary, feline spinal oligoastrocytomas are not frequently reported in veterinary medicine. Although MRI can aid in the diagnosis of a suspected neoplastic lesion, histopathology and immunohistochemistry are mandatory to define the tumor type and determine an accurate prognosis.