Metastatic extradural melanoma of the lumbar spine in a cat

Abstract

A 7-year-old neutered male Domestic shorthair cat, with a 1.5-year history of left eye enucleation secondary to a diffuse iris malignant melanoma, was evaluated for progressive onset of pelvic limb paresis and ataxia with severe thoracolumbar hyperaesthesia and dysorexia. Neurological examination localised a lesion to the T3-L3 spinal cord segments. Magnetic resonance imaging of the thoracolumbar spine showed a well-defined extradural T1-weighted hyperintense non-contrast-enhancing mass, initially suggesting a potential haemorrhagic component. Exploratory surgery revealed a brownish extradural lumbar mass. Histologic examination concluded to a melanoma, most probably metastatic given the animal's previous medical history. This report highlights the importance of collecting a complete medical history, which can help in obtaining a preliminary differential diagnosis in cats with clinical signs of myelopathy. Although the location of this metastasis is particularly unusual both in human and veterinary medicine, making optimal treatment challenging for neurosurgeon, our increased understanding of immune and tumour cell biology during the past decade is likely to improve the future treatments of feline melanoma and its metastases.

Keywords: extradural; feline; immune cell biology; lumbar spine; melanoma; metastatic.

FIGURE 1

Sagittal T2‐weighted image of the cat's lumbar spinal cord showing slightly hypointense and heterogeneous mass (arrowheads) in the dorsal portion of the vertebral canal at the level of the L3–L4 intervertebral space (a). Transverse T2‐weighted image at the level of the L3–L4 intervertebral disc showing the moderately heterogenous hypointense extradural mass (b). Transverse T1‐weighted image at the level of the L3–L4 intervertebral disc showing the hyperintense mass extending within the left L3–L4 foramen (arrow); there is no modification of the vertebral laminae in contact with this mass (c). Transverse T1‐weighted images showing no significant contrast enhancement after injection of contrast product (d).

FIGURE 2

Surgical decompression, before (left) and after (right) mass removing. Note the brownish appearance of the mass (white arrow).

FIGURE 3

Histological section of the extradural mass revealing a dense malignant tumoral proliferation resting on a thin fibrovascular stroma, with cells organised in lobules (arrows) and bundles (arrowheads) (haematoxylin and eosin staining ×100).

FIGURE 4

Histological section of the extradural mass showing round to spindle‐shaped cells, with an abundant eosinophilic cytoplasm rarely containing a small amount of globular brown to black pigment consistent with melanin (arrows) (haematoxylin and eosin staining ×200).