case_images: PMC10107977_01
case_images: (a) Radiograph, (b,c) MRI and (d,e) CT of the lumbar spine of a cat. (a) Right lateral
  radiograph of the lumbar vertebral column obtained 5 months prior to referral. There is
  an expansile, geometrically osteolytic lesion with preserved cortex at the L2-L3
  articular facet joint resulting in a 'soap bubble' appearance (arrow). (b) Mid-sagittal
  T1-weighted imaging after gadolinium administration (T1WI + Gd) and (c) transverse T1WI
  + Gd at the level of the L2 vertebra. There is a large, well-defined extradural mass
  lesion with mild homogeneous contrast enhancement associated with the L2 lamina, caudal
  articular processes and right pedicle (solid arrow). The mass invades the vertebral
  canal, leading to severe right dorsolateral spinal cord compression (dotted arrow).
  (d,e) Mid-sagittal and transverse bone window CT after ioversol contrast at the level of
  the L2 vertebra showing the corresponding L2 mass of soft-tissue attenuation with
  moderate heterogeneous contrast uptake (arrow)
case_images: 10.1177_20551169231160227-fig1.jpg
case_images: PMC10107977_01_10.1177_20551169231160227-fig1.jpg
case_images: fig1-20551169231160227
case_images: Vertebral column radiographs performed by the referring veterinarian revealed an expansile osteolytic lesion of the L2-L3 articular facet joint (Figure 1a). The mass extended into the vertebral canal leading to severe right dorsolateral spinal cord compression. There was a focal, ill-defined intramedullary T2-weighted hyperintensity at this level. The mass had a heterogeneous appearance and was hypointense/isointense in T2-weighted images and isointense on T1-weighted sequences, with mild homogeneous contrast enhancement after gadolinium injection (0.1 mmol/kg [Dotarem; Guerbet Laboratories]) (Figure 1b,c). In agreement with the MRI findings, CT identified an aggressive osteolytic lesion at L2 with strong ioversol contrast uptake (Figure 1d,e).
case_images: Postoperative mid-sagittal three-dimensional CT image of (a) the lumbar spine, (b)
  mid-sagittal bone window CT and (c) transverse bone window CT at the level of the L2
  vertebra. En bloc excision of the tumour was performed, including part of the L2 and L3
  spinous processes, L2-L3 articular facet joints and the majority of the pedicles.
  Titanium screws were placed bilaterally on the pedicles of L1, L2, L3 and L4, and
  embedded in polymethylmethacrylate cement
case_images: 10.1177_20551169231160227-fig2.jpg
case_images: PMC10107977_01_10.1177_20551169231160227-fig2.jpg
case_images: fig2-20551169231160227
case_images: Postoperative CT demonstrated correct placement of the implants and macroscopic resection of the tumour (Figure 2).
case_images: Histopathology of the bone lesion. (a) A thin cap of bone surrounds the tumour (arrow).
  There is bone production (dotted arrow; haematoxylin and eosin [H&E], x 10); (b)
  osteoclast-like multinucleated giant cells (arrows) appear distributed among a
  population of spindle-shaped mononuclear stromal cells (H&E, x 100); (c) the spindle
  cells surround small islands of woven mineralised bone (arrows). The spindle cells do
  not exhibit nuclear atypia or mitotic activity (H&E, x 400); (d) multinucleated
  giant cells show weak cytoplasmic labelling with ionised calcium-binding adaptor
  molecule 1, supportive of monocyte/macrophage lineage (3,3'-diaminobenzidine [DAB]
  chromogen [brown signal] with haematoxylin counterstain, x 400). (e) The majority of the
  spindle cells show nuclear labelling with osterix, supportive of osteoblast lineage (DAB
  chromogen [brown signal] with haematoxylin counterstain, x 400). (f) Both cell
  populations show cytoplasmic labelling with vimentin, a general mesenchymal marker (DAB
  chromogen [brown] with haematoxylin counterstain, x 400)
case_images: 10.1177_20551169231160227-fig3.jpg
case_images: PMC10107977_01_10.1177_20551169231160227-fig3.jpg
case_images: fig3-20551169231160227
case_images: The neoplasm was formed of two cell populations: spindle cells and multinucleated giant cells (Figure 3a,b). Spindle cells predominated, and were arranged in a tightly interwoven storiform pattern surrounding small vessels and multifocally associated with islands and thin trabeculae of woven mineralised bone (Figure 3c). The multinucleated giant cells exhibited weak cytoplasmic labelling with Iba1 (Figure 3d), suggestive of a monocyte/macrophage lineage. Most of the spindle cells showed nuclear labelling with osterix and both cell populations showed cytoplasmic labelling with vimentin (Figure 3e,f).