Page 691 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 31 Tumors of the Nervous System 669

study, the posttreatment neurologic status was the only signifi- tumors are euthanized at or near the time of diagnosis because of
cant prognostic factor where a nonambulatory status was sig- poor prognosis or failure to respond to palliative therapy. 134,135
129
Two dogs with CSAs
nificantly associated with shorter STs.
VetBooks.ir treated with surgery alone both had a recurrence of clinical signs Tumors of Cranial, Paraspinal, and Peripheral
because of imaging confirmed tumor recurrence within 5 months
of surgery. 130 Nerves
Cats with malignant vertebral tumors also have a guarded to
poor long-term prognosis with surgical treatment, with a reported Classification, Epidemiology, and Comparative
MST of 3.7 months in one study. 133 The literature indicates that Pathology
common contemporary veterinary neurosurgical techniques are
generally insufficient to attain the goal of en bloc surgical excision Peripheral nerve tumors (often collectively called peripheral
of vertebral tumors, which is critical to the therapeutic outcome nerve sheath tumors [PNSTs]) are uncommon in dogs and rare in
in humans. 129,130,133 Thus, although currently largely unexplored cats. PNSTs may arise from Schwann cells, perineurial cells, or
in veterinary medicine, aggressive surgical techniques, including intraneural fibroblasts. Descriptive terminology that reflects the
vertebrectomy with vertebral stabilization, will likely become an cellular origin of these tumors (schwannoma, neurofibroma, neu-
important component of advancing the surgical treatment of ver- rofibrosarcoma) is not routinely used because of the inherent level
tebral and SC tumors. 153 of difficulty in determining the tissue of origin of these tumors
Currently, there is insufficient information to clearly identify in veterinary medicine. Instead, PNSTs are divided into benign
the superior method of treatment of solitary vertebral plasma cell peripheral nerve sheath tumors (BPNSTs) or malignant peripheral
tumors in dogs and cats. Solitary plasmacytomas have been treated nerve sheath tumors (MPNSTs) based on microscopic evidence of
successfully with surgery, RT, and various combinations of these malignancy. 157–159 This latter classification scheme is more use-
modalities. 132,154 ful from a clinical standpoint, as the majority of reported PNSTs
Dogs with nephroblastomas treated with surgery and RT may in dogs are histologically and biologically aggressive tumors. Cats
also experience improved functional outcomes and STs compared have a higher proportion of BPNSTs compared with dogs. 158
with those not treated surgically, although reported MSTs vary PNSTs may arise in any cranial nerve, spinal nerve root, or
widely. 142,143 In one study, MST for dogs that were not treated somatic or autonomic peripheral nerve. 157–160 PNSTs occur most
surgically was 1 day compared with 71 days for dogs that under- commonly in middle-aged to older dogs of medium and large
went cytoreductive surgery. 142 Another investigation reported that breeds. No breed or sex predilection has been noted. The most
dogs with nephroblastoma treated with cytoreductive surgery or frequently affected cranial nerve is the trigeminal nerve, and the
RT survived longer (MST 374 days) than dogs treated palliatively most common spinal nerve roots affected are in the caudal cervical
(MST 55 days). 143 Tumors confined to an ID-EM location were region (C6–T2) followed by nerves of the lumbar intumescence
associated with superior STs (MST 380 days) than tumors with (Fig. 31.7). 157–160 Metastasis is rare. Secondary tumors, such as
IM involvement (MST 140 days). 143 As nephroblastoma affects lymphoma, malignant sarcomas, HS, and hamartomas, can occa-
young dogs, the literature suggests that the majority of dogs will sionally involve peripheral nerves. 136,138,139 In cats, diffuse infiltra-
experience life-limiting local tumor recurrence or treatment com- tive peripheral nerve lymphoma (neurolymphomatosis) is usually
plications regardless of treatment type. 142,143 B-cell origin, but one case of peripheral T-cell lymphoma in an
The outcomes associated with other specific types of SC tumors FeLV-positive cat has been reported. 161,162 In dogs, peripheral
are unknown owing to very limited numbers of reported cases that nerve lymphoma is typically of T-cell origin. 136
received treatment, and in some instances, cases received RT treat-
ment without histologic confirmation of the type of lesion being Pathophysiology, History, and Clinical Signs
treated. 155 A few case reports suggest that primary IM neuroep-
ithelial neoplasms may be resected if well-demarcated and that As with brain and spinal tumors, the clinical signs of PNSTs reflect
long-term successful outcomes are possible with combinations of the location of the tumor. As the majority of reported canine
surgery, with and without RT. 156 However, most animals with IM PNSTs involve the nerve roots and/or nerves of the brachial and

A B C D

• Fig. 31.7 MRI and pathologic features of PNST. (A) Postcontrast MRI of C7 MPNST manifesting as thick-
ening and contrast enhancement of the affected nerve, as well as intradural invasion. (B) At necropsy, a
MPNST appears as nodular masses on the C7, C8, and T1 nerves. Bar = 1.5 cm. (C) Dorsal MRI image of
a sciatic PNST causing enlargement of hyperintensity of the affected nerve (arrow). (D) MRI of a trigeminal
PNST with compression of the midbrain and atrophy of the muscles of mastication ipsilateral to the tumor.