History
A 6-year-old spayed female Basset Hound was presented for a 2-day history of subacute paraplegia. No trauma or injury was reported by the owners. Other pertinent medical history includes regional mastectomy due to mammary carcinoma 9 months prior. On neurological assessment, the dog was nonambulatory with an absence of proprioception and voluntary motor function, normal spinal reflexes, and conserved conscious pain sensation. Neurologic assessment of the forelimbs was normal. These findings were consistent with compressive or noncompressive myelopathy, localized in the T3-L3 spinal cord segment.
Diagnostic Imaging Findings and Interpretation
To exclude gross pulmonary metastatic processes given the history of mammary carcinoma, right-to-left lateral thoracic radiography was performed. No pulmonary metastasis was seen, but expansile osteolytic lesions were observed in the extremities of the spinous processes of T2, T6, and T7 (Figures 1 and 2).
Right-to-left lateral radiograph of the thoracic vertebral column of a 6-year-old spayed female Basset Hound with a 2-day history of subacute paraplegia.
Citation: Journal of the American Veterinary Medical Association 261, 10; 10.2460/javma.23.05.0252
Same radiographic image as in Figure 1. Large, lytic, expansile lesions are present in the dorsal aspects of the T2, T6, and T7 spinous processes (black arrows).
Citation: Journal of the American Veterinary Medical Association 261, 10; 10.2460/javma.23.05.0252
Considering the patient’s history, the main hypothesis for multifocal expansile osteolytic thoracic vertebral lesions was bone metastases. However, bone metastases in the vertebral spinous processes are rare. The differential diagnoses included round cell tumor, enchondromatosis, multiple cartilaginous exostosis, giant cell tumor, bone abscesses, benign bone cysts, aneurysmal bone cysts, and fibrous dysplasia. Bone abscesses seemed to be less likely because of the clinical examination and the normal blood count.
A CT scan of the vertebral column was performed from C5 to Co4 and confirmed expansile osteolytic lesions in the dorsal aspects of the T2, T6, and T7 spinous processes with a permeative aspect of some areas of lysis. These osteolytic lesions were soft tissue attenuating and homogeneously contrast enhancing, causing outward expansion and thinning of the cortices of the spinous processes (Figure 3), which ruled out the cyst-like lesion as a differential diagnosis. A large, vascularized mass was observed in the body of T13, associated with severe lysis of two-thirds of this vertebral body, the right dorsal arch, and the right cranial articular process. This mass invaded the vertebral canal at the level of T13 (90%), causing severe dorsal and leftward displacement and compression of the spinal cord. Multiple nonexpansile lytic areas were also present in several additional vertebrae (vertebral body of C7, T6, T8, L1, and S1; transverse process of S2; articular process of C5 and L4), in the left femoral head, and in the wing of the left ilium. Enhancing nodules were also observed in the left iliocostalis thoracis muscle.
A—CT transverse image displayed in a bone window at the level of T2. Note the severe expansile lysis of the dorsal aspect of the T2 spinous process with the soft tissue–attenuating osteolytic lesion arising within the bone and displacing the cortex outward to cause thinning of the cortex. B—CT transverse reconstruction image displayed in a soft tissue window following contrast medium administration, at the level of T13 and of the compressive mass. Note the large enhancing mass (black star) lysing the T13 vertebral body, right cranial articular process, and right pedicle. The spinal cord is displaced in a leftward direction and is severely compressed (arrowhead).
Citation: Journal of the American Veterinary Medical Association 261, 10; 10.2460/javma.23.05.0252
The lumbar aortic, medial iliac, internal iliac, sciatic, and sacral lymph nodes were markedly enlarged, and some were heterogeneously contrast enhancing. No nodule or mass was observed in the part of the lung and abdomen included in the study.
Treatment and Outcome
Due to a poor prognosis, the dog was euthanized. Postmortem core biopsies were obtained from the T6 and T7 spinous processes. Histopathology and immunochemistry were consistent with metastases of tubulopapillary carcinoma.
Postmortem T3-L3 MRI was performed, obtaining T1-weighted, T2-weighted, and STIR sequences in all planes to further document the case. Within the body of T13, a mass that was hyperintense to the vertebral body on all sequences was seen (Figure 4). Expansile lytic lesions were observed in the dorsal part of the T6 and T7 spinous processes. These lesions were hyperintense compared with the vertebral bodies on all sequences.
A—Transverse T2-weighted MRI image at the level of T13 and the compressive mass. Note the large mass (white star) lysing the T13 vertebral body, right cranial articular process, and right pedicle. The spinal cord is displaced in a leftward direction and compressed (white arrow). B—Sagittal T2-weighted MRI image of the midaspect of the thoracic vertebral column. Note the severe expansile lysis of the dorsal aspect of the T6 and T7 spinous processes.
Citation: Journal of the American Veterinary Medical Association 261, 10; 10.2460/javma.23.05.0252
Comments
The imaging exams of this patient showed multiple lytic bone lesions affecting mainly the vertebral column. The T13 lesion led to spinal cord compression and was the cause of the clinical signs. The expansile aspect of the spinous process lesions could suggest lesions that were benign or of low-grade malignancy. However, considering the patient’s history, all these lesions were most likely compatible with vertebral metastases.
Mammary neoplasia is the most common malignant tumor in female dogs. In intact females, they represent 40% of all tumors.1 Tubulopapillary carcinoma is a subtype of simple mammary carcinoma. The most common metastatic sites are regional lymph nodes, lungs, and liver. Other sites include bone, brain, spleen, kidney, skin, eye, adrenal glands, uterus, heart, muscle, and pancreas. In human medicine, bone metastases are more frequent than primary bone tumors, and the skeleton is the most common site of breast cancer metastases, with approximately 80% of patients with breast cancer who died having bone metastases. A veterinary study2 found skeletal metastasis in 20% of patients with canine mammary tumors. Sites of metastasis included vertebrae, the femurs, and humerii.2 Metastases were observed in only thoracic and lumbar vertebral bodies and, rarely, in spinous processes,2 but scarce descriptions were made concerning the location and the aspect of the spinous process metastases. Only 1 case report3 described an expansile lesion in the apex of the T1 spinous process in a dog. This lesion was due to a multiple myeloma. Another case report4 described carcinoma metastases in a horse, affecting the C1 spinous process. Carcinoma metastases have an affinity for vascularized bone marrow of the vertebral bodies, and the main way of dissemination of metastasis in vertebrae is hematogenous, which could explain why the apex of spinous processes is less commonly affected by metastases.
Expansile lesions are consequences of masses arising within the bone that displace and thin the cortex. Other differential diagnoses for expansile lytic lesions in vertebrae include giant cell tumors, aneurysmal bone cyst, benign bone cysts, enchondroma, osteochondroma, fibrous dysplasia, bone abscess, and, rarely, other nonosteogenic malignancies. Aneurysmal bone cysts are expansile, multiloculated lesions resulting from vascular malformation. They are rare and occur predominantly in young dogs. Benign bone cysts are benign, fluid-filled, cystic lesions that most commonly appear in the metaphyseal or diaphyseal region of long bones, but have been described in spinous processes in human medicine.5 They can be monostotic or polyostotic and are usually observed in young patients. Giant cell tumors are rare tumors found in old dogs, affecting the epiphyses and metaphyses of long bones. Other sites, such as vertebrae, can be occasionally observed especially in the multicentric form. Fibrous dysplasia is a rare pathology due to the replacement of the medullary component of 1 bone or several bones with fibrous connective tissue. Vertebral fibrous dysplasia was reported in human literature, but with no involvement of the spinous or transverse processes or articular facets. Endochondroma is a rare bone disease characterized by lobulated islets of partially mineralized cartilage located within the metaphyses of the long bones, which can extend through the metaphysis into the diaphysis. Endochondroma distorts the normal cancellous bone pattern. Finally, osteochondromas appear as smooth, cauliflower-like, or nodular lesions with cortex and medulla in continuity with the underlying bone. No cystic component was observed on the CT scan in our case. Furthermore, all the lesions enhance on postcontrast images, excluding several hypotheses. The remaining differential diagnoses for expansile lesions included uncommon giant cell tumors, osteochondroma, or metastases. Osteomyelitis was deemed less likely due to the clinical examination and blood count. Only the expansile lytic lesions affecting the spinous processes were visible on the thoracic radiographs and were not responsible for the clinical signs. Even if the main hypothesis was bone metastases because of the patient’s history, discrimination between the hypotheses was not possible with radiographs. A CT scan allowed the visualization of the large compressive vertebral mass responsible for the clinical signs and suggesting an aggressive process. Other metastatic sites were observed thanks to the CT scan (bone, lymph nodes, muscle). It also permitted the ruling out of some hypotheses for the expansile lesions in part because of the permeative aspect of some areas of lysis, the lesion enhancement, and the absence of cystic components. Even if polyostotic cases have been described for the other causes of expansile bone lysis, they are most often monostotic and rare.
In conclusion, bone metastases due to mammary carcinoma are uncommon in dogs and are typically observed in vertebral bodies when vertebrae are involved.
Expansile spinous process metastases had not been described in canine mammary carcinoma. Therefore, when an expansile osteolytic lesion is observed on radiographs, bone metastasis should be considered as a differential diagnosis, particularly if a mammary tumor is reported in the dog’s history.
Acknowledgments
None reported.
Disclosures
The authors have nothing to disclose. No AI-assisted technologies were used in the generation of this manuscript.
Funding
The authors have nothing to disclose.
References
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