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Chapter 27: Surgical Management of Spinal Neoplasia 241

result in prolonged survival in some instances. Nerve sheath tumors thoracic spine, the hypothesis being that arachnoid cap cells are
(see Figure 27.7) typically have a much worse long‐term prognosis believed to be the progenitor cell for meningiomas and that these cells,
with surgery alone [7]. In general, cats with nonlymphoid spinal which are found within arachnoid proliferations, are most commonly
neoplasia tend to have a much better prognosis than cats with spinal located in the thoracic spine in humans [13]. This makes surgical
lymphoma [1]. resection the treatment of choice and the need for follow‐up therapy
As with any tumor of the bone, the more complete the resection such as radiation unusual. In humans, recurrence of spinal meningi-
the better the chances of a longer‐term prognosis. The location of omas after surgical resection has been reported to be as low as 3–15%
the tumor in the vertebral body plays a large part in the overall [14]. In humans, about 25% of all primary spinal cord tumors are
success of removal. In general, tumors located dorsally or Zone 1 meningiomas, and these usually occur in people in their fourth decade
[12] are the easiest to remove and therefore probably have the best [4]. Young dogs, usually less than 3 years of age, have a propensity to
chance of complete excision. With regard to vertebral tumors, the form primitive neuroectodermal tumors (PNETs). These tumors are
biggest prognostic indicator is length of time to treatment. Dogs all considered biologically malignant and are able to differentiate into
with the shortest duration of clinical signs and therefore the less neuronal, glial, or ependymal cell lines [15]. Recently, some of these
time for invasion and metastasis had the best long‐term survival. PNETs have been differentiated with the aid of positive immunohisto-
Overall, primary spinal cord tumors occur infrequently in dogs. chemical staining for Wilms tumor gene product (WT1) which is a
Meningiomas are the most common primary spinal tumor in dogs, human marker for human nephroblastoma (Wilms tumor) into extra-
and these seem to have a predilection for the cervical region. In a renal nephroblastomas. Typically, extrarenal nephroblastoma occurs
recent study of 34 intraspinal meningiomas, they were further clas- in younger dogs aged between 5 months and 7 years, with 6–36
sified into three different histological categories. These categories, months the most common age. They are also found almost exclusively
as previously noted in humans, show a significant correlation with between T10 and L2 spinal vertebrae [6,10,11,15,16]. German
both tumor location and long‐term survival. Moreover, cervical Shepherds and Golden Retrievers are the most common breeds. The
meningiomas tended to exhibit the less aggressive grade I form, most common type of spinal tumor in cats is spinal lymphoma, and
whereas thoracolumbar and lumbar meningiomas tended to be usually occurs in younger patients. Other types of spinal tumors in
grade II or III. In general, the higher the grade the worse the prog- cats have been reported as well but they usually occur in older cats [1].
nosis for patients with spinal meningioma. Grade III tumors are Osteosarcoma is the most common vertebral bone tumor in dogs and
much less common than grade I or II. Higher cervical meningiomas cats while in humans it is rare. Dogs and humans tend to have a much
(i.e., C3 or cranial) while having a lower grade can often make sur- poorer prognosis than cats with osteosarcoma [2,11].
gery more hazardous because of the critical location (brainstem)
and more difficult resection [13]. Younger dogs were more likely to
have grade II meningiomas and these grade II tumors tended to be Nonsurgical Therapy
in the thoracolumbar region. Older dogs tended to have grade I Other forms of therapy such as radiation therapy, chemotherapy
tumors and these tended to be in the cervical region. In comparison and symptomatic care have been used. Radiation therapy is often
with humans, most spinal meningiomas are grade I and are usually recommended in addition to surgery or when surgery is not possi-
well encapsulated. The most common location in humans is the ble or viable. Radiation typically is used for local control. Depending

A B

Figure 27.9 (A) Surgical removal of an intramedullary mass in the lumbar region of a dog following a dorsal laminectomy and durotomy. (B) Preoperative
transverse T1‐weighted MRI with contrast showing the mass (arrow).