Page 304 - Canine Lameness

276 17 Neoplastic Conditions of the Thoracic Limb

meningeal sarcoma. Tumors reported to metastasize to the substance of the spinal cord are heman-
giosarcoma, mammary gland carcinoma, malignant melanoma, and thyroid carcinoma. Antemortem
confirmation of a diagnosis of an intramedullary tumor can be challenging and carries risks of wors-
ening the neurologic status. For these reasons, it is rarely attempted. Nonetheless when it is attempted,
it may be done with a needle aspirate or biopsy. A small gauge needle is preferred but it limits the
diagnostic ability of the procedure. A biopsy can be obtained through a laminectomy or hemilami-
nectomy approach followed by a durotomy.
Intradural‐extramedullary neoplasms arise outside the spinal cord but are within the subdural
space. The most common tumors are nerve sheath tumor, meningioma, and hemangioma.
Antemortem diagnosis is possible with a needle aspirate or biopsy; minimally invasive CT‐guided
techniques may be feasible in selected cases. A biopsy also requires a laminectomy or hemilami-
nectomy approach to the lesion.
Extradural neoplasms originate outside the dura mater and include osseous and soft tissue neo-
plasia. Lymphoma is the most common soft tissue extradural tumor. Other soft tissue tumors
found in this location include meningioma, nerve sheath tumors, myxoma, myxosarcoma, plasma
cell tumor, and lipoma.
Osseous tumors include osteosarcoma, fibrosarcoma, hemangiosarcoma, multiple myeloma,
and chondrosarcoma. Osteosarcoma, fibrosarcoma, and hemangiosarcoma of the vertebrae may
also be a metastasis and therefore evaluation for a primary neoplasm should be performed. Other
tumors may metastasize to soft tissues adjacent to the vertebrae and cause secondary spinal inva-
sion and eventually compression. Malignancies can also metastasize directly to the vertebrae via
the hematogenous route. An example of the former would be metastasis from prostatic adenocar-
cinoma to the sublumbar lymph nodes and eventually invasion into the lumbar vertebrae.
Numerous other neoplasms can metastasize to vertebrae and include mammary carcinoma, peri-
anal gland adenocarcinoma, transitional cell carcinoma, Sertoli cell carcinoma, thyroid carcinoma,
and pheochromocytoma. The lumbar area is the most common site for spinal metastasis, but the
cervical and thoracic segments can also be affected.
Extradural spinal cord tumors can generally be diagnosed with a needle aspirate or biopsy. Either
procedure can be performed with a surgical approach to the lesion or image guidance with either
CT or ultrasound.

17.2.5.2 Peripheral Nerve Tumors
Tumors originating from the peripheral nervous system are termed peripheral nerve sheath
tumors. These include schwannoma, neurofibroma, perineurioma, and malignant peripheral
nerve sheath tumors (MPNST). The majority of tumors are MPNST and are biologically aggressive
by exhibiting local invasion but rarely metastasize. Being that MPNST are soft tissue sarcomas,
grade is prognostic for local recurrence and metastatic potential. These tumors can be affecting a
nerve root, spinal nerve, or the brachial plexus or be distal to the brachial plexus. The location rela-
tive to the brachial plexus (distal, within, or proximal) has prognostic value with tumors distal to
the plexus having the best prognosis (Brehm et al. 1995).
Diagnosing these tumors can be challenging, since the only clinical sign can be lameness, which
can be mild or severe. Some dogs will show a lack of weight‐bearing while standing (i.e. lift their
leg, Video 4.1), yet the lameness improves during ambulation. This has been termed “nerve root
signature lameness” and is thought to be due to compression of inflammation of a nerve root. Pain
while manipulating the neck can be detected if the tumor is present in the spinal canal and causing
cord compression. Presence of a partial Horner syndrome or loss of panniculus reflex will raise
the suspicion of a lesion proximal to the brachial plexus (Chapter 4) but their absence does not
rule it out. Muscle atrophy is usually significant (neurogenic atrophy), in fact moderate‐to‐severe