Tumors of the Nervous System - Tumors of Cranial, Paraspinal, and Peripheral Nerves Flashcards
Frequency of PNST in dogs and cats ?
Peripheral nerve tumors (often collectively called peripheral nerve sheath tumors [PNSTs]) are uncommon in dogs and rare in cats
Cells of origin for PNSTs ?
PNSTs may arise from Schwann cells, perineurial cells, or intraneural fibroblasts. Descriptive terminology that reflects the cellular origin of these tumors (schwannoma, neurofibroma, neurofibrosarcoma) is not routinely used because of the inherent level
of difficulty in determining the tissue of origin of these tumors in veterinary medicine
Classification of PNSTs in vet med ?
Instead, PNSTs are divided into benign
peripheral nerve sheath tumors (BPNSTs) or malignant peripheral nerve sheath tumors (MPNSTs) based on microscopic evidence of
malignancy.157–159 This latter classification scheme is more useful from a clinical standpoint, as the majority of reported PNSTs in dogs are histologically and biologically aggressive tumors
Which specie has more benign PNST ?
Cats
What location is possible with PNST ? Breed predilection ? Signalment ?
PNSTs may arise in any cranial nerve, spinal nerve root, or somatic or autonomic peripheral nerve.157–160 PNSTs occur most commonly in middle-aged to older dogs of medium and large breeds. No breed or sex predilection has been noted.
Most common cranial nerve affected by PNST ? Most common location in spine ?
The most frequently affected cranial nerve is the trigeminal nerve, and the most common spinal nerve roots affected are in the caudal cervical region (C6–T2) followed by nerves of the lumbar intumescence
Metastatic rate of PNST ?
Metastasis is rare
Secondary tumors that affect peripheral nerves ?
Secondary tumors, such as
lymphoma, malignant sarcomas, HS, and hamartomas, can occasionally involve peripheral nerves
Immunophenotype of peripheral LSA in cats ? Dogs ?
In cats, diffuse infiltrative peripheral nerve lymphoma (neurolymphomatosis) is usually B-cell origin, but one case of peripheral T-cell lymphoma in an
FeLV-positive cat has been reported.161,162 In dogs, peripheral nerve lymphoma is typically of T-cell origin
typical clinical signs of PNST ?
classic clinical scenario is one of chronic lameness without identifiable orthopedic abnormalities.163,164 The etiology of the observed clinical signs may remain elusive for months and may not be appreciated until signs progress to monoparesis with neurogenic atrophy or signs of spinal cord disease appear.
Signs of myelopathy are often asymmetric and occur when the mass invades the vertebral canal and compresses or invades the SC. Clinical signs of pain on palpation or paresthesia are also common.
Clinical signs of trigeminal PNST ?
Trigeminal PNSTs cause signs of severe, unilateral masticatory
muscular atrophy, diminished jaw tone, decreased facial sensation,
and Horner’s syndrome.160 Brainstem involvement may result in
other regional cranial nerve deficits and long tract signs depending
on size and invasiveness of the mass
Peripheral nerve LSA clinical signs ?
Peripheral nerve lymphoma may present with a clinical history similar to PNST or with neurolymphomatosis. In the latter scenario, flaccid tetraparesis and hyporeflexia can reflect the diffuse neoplastic inflitrative neuropathy
% of brachial PNST palpable on physical exam ?
Approximately 33% of cases with PNST affecting the brachial plexus will have a palpable mass on physical examination
Imaging modality for brachial PNST ?
Ultrasound of the axillary region appears to be more sensitive for
the detection of mass lesions than palpation, but not as useful as
MRI.
Diagnostic modalities for PNST ? What % only show nerve thickening rather than mass ?
PNST can be challenging to diagnose, and exploratory
surgery and biopsy is sometimes required. The most useful imaging tool for diagnosing PNST and discriminating other etiologies of the observed clinical signs is MRI, whether the lesion involves a plexus, the SC, or a cranial nerve, although CT-myelography is described.160,166 To facilitate the diagnosis of PNST, cross-sectional imaging should include sequences
with a wide field of view to incorporate the plexi and limb structures (see Fig. 31.7C). On MRI examinations of PNST cases, up to 50% of patients display only nerve thickening rather than a discrete mass (see Fig. 31.7A).160,166,167 Postcontrast sequences are particularly helpful in the identification of
subtle tumors
Differential diagnosis for PNST-like lesions on MRI ?
Idiopathic neuritis, hypertrophic ganglioneuritis, and peripheral nerve lymphomas may have an identical
appearance on MRI to PNST
Preferred treatment in dogs and cats ?
Surgery is the preferred treatment of PNSTs in dogs and cats
What are 2 negative prognostic factors ?
Proximity to and invasion into the vertebral
canal, which occurs in 45% of dogs, and the presence of tumor
infiltrated margins after compartmental resection are negative
prognostic indicators
% of invasion into vertebral canal ?
45%
MST for canine paraspinal and plexus PNST ?
In dogs, the overall prognosis historically is considered guarded to poor, with MSTs of approximately 6 months for dogs with paraspinal and plexus PNST, reflecting the more malignant biologic behavior of canine PNST. Long-term survival is possible after complete resection of tumors,163 including the use of limb sparing techniques (MST 1303 days
MST of PNST using VMAT RT (dogs)
Recently, a study investigating VMAT radiotherapy for the treatment of canine PNST reported outcomes that were superior to earlier reports of surgically treated dogs with evidence of nerve root and vertebral canal invasion, with a mean progression-free ST of 8 months.
Prognosis for feline PNST ? benign and malignant recurrence rate ?
The prognosis for cats is more favorable. In
one study of 45 surgically treated cats, 31% (5/16) of MPNST recurred compared with 14% (4/43) of BPNST.158 Treatment failures typically manifest as neurologic signs attributed to local recurrence.
Canine trigeminal PNST prognosis ? Alone or with RT ?
Canine trigeminal PNST may have an insidious clinical
course, with some untreated dogs experiencing STs in excess of 18 months without significant clinical progression.160,167,171
Trigeminal PNSTs may be surgically removed or irradiated and successful outcomes have been reported for both treatment modalities.160,167,171 The MSTs for dogs with trigeminal PNST treated with SRS or SRT is reported as 745 days167 and 441
days.171 RT may be superior to palliative and surgical treatment, particularly with respect to resolving neurologic signs in cases with clinical and imaging evidence of brainstem involvement
Peripheral nerve LSA treatment ?
Peripheral nerve lymphomas, which may be indistinguishable from PNST, may respond to radiation or chemotherapy, although no current literature provides specific treatment recommendations or outcomes of dogs or cats with peripheral nerve lymphoma or neurolymphomatosis.
