BENIGN TUMORS


Osteochondroma

•osteochondroma is an uncommon condition in skeletally immature dogs presenting with neurologic disease

•2 forms: solitary or multiple (i.e., multiple cartilaginous exostoses)

•osteochondromas originate in the dorsal elements of the spine (i.e., lamina and dorsal spinous processes)

•vertebral osteochondroma has been reported in 3 cats and 6 dogs

•site: thoracic vertebral column

•survey radiographs: osteochondromas are well circumscribed lesions with no bony lysis or proliferation

•malignant transformation of solitary osteochondroma to OSA has been reported in 2 dogs


Vascular Malformation

•synonyms: skeletal angiomatosis and hemangioma

•vascular malformation may be capillary, venous, lymphatic, or arterial

•arterial lesions are high-flow whereas be capillary, venous, and lymphatic lesions are low-flow

•6 categories of vascular malformations have been described:

•bone distortion

•bone destruction or erosion

•hypertrophy

•hypoplasia

•density changes (i.e., sclerosis or demineralization)

•primary involvement of vessels within bone

•high-flow lesions may also have destructive, intraosseous, and lytic changes

•lytic bone lesions have been described in 3 cats



MALIGNANT TUMORS


General Considerations

•malignant bone tumors are more common than benign tumors

•OSA is the most common vertebral bone tumor

•other malignant vertebral bone tumors include CSA, FSA, HSA, LSA, carcinoma, liposarcoma, and giant cell tumor


Osteosarcoma

•vertebral OSA accounts for up to 16% of axial OSA and is the most common extradural spinal neoplasm (46%)

•multiple vertebral involvement is reported in 25% dogs

•OSA in 2 adjacent lumbar vertebra has been reported

•skip metastases are secondary foci of malignant tumor which are anatomically separate from the primary lesion, but found in the same bone or opposite side of the adjacent joint

•skip metastases are considered systemic with a prognosis the same or worse than pulmonary metastases

•multifocal OSA is a condition in humans with multiple intraosseous foci of OSA (which may be representative of either multicentric OSA or rapidly metastatic OSA)

•metastatic potential not known due to early and catastrophic consequences of primary lesion

•surgical excision is complicated by tumor location and proximity to adjacent vital structures

•MST 135 days following multimodality therapy with surgery, chemotherapy, and radiation therapy


Plasma Cell Tumor and Multiple Myeloma

•plasma cell tumors account for < 4% of vertebral tumors

•2 types of plasma cell tumor: solitary and multiple myeloma

•plasma cell tumors have a predilection for marrow-containing bone of the axial skeleton

•25% of dogs with multiple myeloma have vertebral involvement

•breed predisposition: purebred dogs

•sex predisposition: male

•clinical signs: spinal pain and neurologic deficits

•diagnosis: survey radiographs ± CT or other advanced imaging

•50%-67% have evidence of osteolysis or diffuse osteoporosis, especially in the vertebrae, pelvis, skull, and ribs

•normal or reduced radionucleide uptake with bone scintigraphy

•treatment: melphalan and prednisolone

•radiation therapy and chemotherapy are recommended for vertebral plasma cell tumors in humans as these 2 treatment modalities significantly decrease the frequency of metastatic disease and prolong survival time

•surgical excision is recommended for solitary plasmacytoma in humans if neurologic deficits are severe


Metastatic Tumors

•metastatic tumors are diagnosed on the basis of location of primary tumor ± evidence of more than 1 lesion

•primary tumors metastatic to vertebrae include carcinomas of various sites (especially urothelial and prostate), multicentric and mediastinal LSA, and sarcomas such as HSA and OSA

•intrapelvic metastases result in new bone formation on the ventral aspect of the vertebral bodies and a paravertebral soft tissue mass

•metastases from intrapelvic neoplasia are common because vertebral venous drainage is valveless and closely associated with adjacent soft tissue and increased abdominal pressure results in shunting of venous return (and tumor emboli) from the caudal vena cava into the vertebral sinus system



CLINICAL FEATURES


Signalment

•median age 6-8 years for primary vertebral tumors and 8-9 years for metastatic tumors

•sex predisposition: male

•vertebral tumors occur more commonly in large breed dogs with only 5% dogs < 20 kg

•vertebral tumors occur more commonly in the thoracic and lumbar vertebrae


Clinical Signs

•pain without neurologic deficits the most common clinical presentation

•pain can be difficult to localize (i.e., generalized and non-specific, regional, referred, or localized)

•primary and secondary vertebral tumors eventually present with partial or complete transverse myelopathy

•time to progression from pain to myelopathy can be long

•acute onset of neurologic disease is seen with pathologic fracture

•neurologic scoring system: 1. pain, 2. weakness, 3. ataxia and loss of conscious proprioception, and 4. paralysis


Diagnosis


Survey Radiographs

•survey radiographic findings include cortical lysis with collapse of the adjacent intervertebral disk space

•radiographic signs may not always visible due to inconsistent vertebral shape, overlying ribs and soft tissue, and improper positioning

•cortical bone destruction is a late event in metastatic vertebral lesions


Myelography

•myelographic findings include collapse of the subarachnoid space, cord displacement or shifting and unilateral or asymmetric displacement of the spinal cord


Advanced Imaging

•CT, MRI, or bone scintigraphy may be required to provide earlier evidence of metastatic disease

•paravertebral soft tissue mass is often present with 24% secondary to intrapelvic tumors

•MRI provides accurate information on anatomic location and degree of bone involvement, but differentiation between intradural, extradural-intramedullary, and extramedullary lesions is difficult

•hypointense signal for vertebral tumors on T1-weighted images provides the best information


Biopsy

•open biopsy via laminectomy is contraindicated in the diagnosis of human vertebral tumors as contamination of the epidural space increases the risk of local tumor recurrence

•transpedicular approach, with subsequent filling of the defect with bone cement, or CT-guided bone biopsy are the preferred techniques


Surgery


General Considerations

•treatment options: surgery, radiation therapy, and chemotherapy (systemic ± intralesional) alone or in combination

•radiation therapy is considered essential in the treatment of vertebral tumors in humans and radiosensitizers may enhance effect of radiation therapy

•3 major types of en bloc excision:

•vertebrectomy

•sagittal resection

•resection of the dorsal lamina

•surgical resection is based on the degree of tumor involvement in the vertebra and tumor aggressiveness


Vertebrectomy

•vertebrectomy is indicated for centrally located tumors and tumors with 1 pedicle free from tumor (i.e., zones 4-8 or 5-9)

•vertebrectomy can be performed in 1 or 2 stages, with 2-stage procedures preferred

•dorsal approach is used for resection of the annulus fibrosus and dorsal longitudinal ligament, hemostasis of the epidural venous plexus, and stabilization

•ventral approach is used for hemostasis of the segmental vessels, cranial and caudal diskectomies, en bloc removal of vertebral body, and reconstruction and stabilization

•stabilization techniques include DCP, multiple-level Harrington rod fixation, wire fixation of facets and spinous processes, interbody fusion, and acrylic fixation

   •vertebrectomy has been reported in 1 dog with vertebral FSA


Sagittal Resection

•sagittal resection is indicated for eccentrically located tumors in the vertebral body, pedicle, or transverse process (i.e., zones 3-5 or 8-10)

•combined dorsal and ventral approach, as described above, permits access to 300° of the vertebra

•nerve root or roots are ligated as necessary

•vertebrectomy is performed 1 zone away from the tumor margins


Dorsal Lamina Resection

•dorsal lamina resection is indicated for tumors in which the pedicles are not involved (i.e., zones 10-3)

•wide dorsal laminectomy

•surgery is often intralesional (i.e., laminectomy) without curative intent and stabilization may be required


Prognosis

•MST 135 for malignant vertebral tumors

•prognostic factors include preoperative neurologic score, postoperative neurologic score, and treatment intent

•MST is increased with a preoperative neurologic score of 1 (330 days v 120 days)

•MST is significantly increased with a postoperative neurologic score of ≤ 2 (135 days v 15 days)

•MST is significantly longer for dogs treated with curative-intent radiation therapy compared to palliative radiation therapy (150 days v 15 days)

•dogs with postoperative neurologic score of ≤ 2 are 12-times more likely to survive

•factors that are not prognostic include:

•tumor type: MST 113 days for vertebral OSA and 135 days for FSA

•tumor location: MST 90 days for cervical, 150 days for thoracic, and 135 days for lumbar vertebral tumors

•primary tumors (MST 120 days) and metastatic tumors (MST 135 days)

•chemotherapy: MST 135 days with chemotherapy and 150 days with no chemotherapy

•radiation therapy: MST 150 days with radiation therapy and 15 days with no radiation therapy

•combined treatment: MST 135 days with combined treatment and 38 days with no treatment

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T0

No evidence of neoplasia

T1

Tumor confined within the medulla and cortex

Primary Tumor

T2

Tumor extends beyond the periosteum

M0

No evidence of lymph node involvement

M1

Evidence of distant metastasis with site specified

Metastasis