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Nerve Sheath Tumors 693

PHYSICAL EXAM FINDINGS ○ Determine specific nerve roots involved Possible Complications
to aid in surgical planning.
Varies with respect to tumor location and nerve • Cerebrospinal fluid (CSF) evaluation (pp. • Local invasion into adjacent tissues (e.g.,
VetBooks.ir • Localized muscle atrophy (often severe): 1080 and 1323): occasionally, albuminocyto- • Metastatic rates for nerve sheath tumors have Diseases and Disorders
brainstem, spinal cord)
root(s) affected; abnormalities can include
involving thoracic limb with tumor of
logic dissociation (disproportionate elevation
not been established, although they appear
brachial plexus and involving mastica-
nucleated cell count)
tory muscles with tumor of trigeminal in CSF protein concentration compared with to be low.
nerve • Myelography Recommended Monitoring
• Progressive lameness and/or weakness ○ May indicate local invasion into spinal Monitor for progressive/recurrent neurologic
• Proprioceptive deficits canal deficits and/or pain.
• Hyporeflexia ○ Can rule out lateralized disk herniation
• Sensory deficits • Advanced imaging PROGNOSIS & OUTCOME
• Pain on palpation of tumor site (e.g., axilla) ○ MRI (p. 1132) is the preferred modality
• Ipsilateral loss of cutaneous trunci reflex (can for identifying soft-tissue and intracranial • Varies; histopathologic grade, tumor loca-
occur with involvement of C8-T1 spinal lesions. However, a normal MRI scan does tion (surgical accessibility), and stage are
segments) not completely rule out a small or diffuse prognostic.
• Ipsilateral Horner’s syndrome (can occur nerve sheath tumor. • Although complete excision can be cura-
with cervical or brachial plexus nerve sheath ○ CT can be particularly useful in evaluating tive, local invasion into the spinal cord or
tumors) compressive spinal lesions when performed brainstem often has already occurred by the
in conjunction with a myelogram. time of diagnosis, making cure unlikely.
Etiology and Pathophysiology • Fine-needle aspiration for cytologic exam ○ For tumors close to the spinal cord, the
Undetermined; a point mutation in the neu • Biopsy (percutaneous or surgical excision) median postoperative survival time is
oncogene has been suggested. • Tumor staging 5-6 months, with a disease-free interval
○ Thoracic radiographs of about 1 month.
DIAGNOSIS ○ Abdominal ultrasound ○ Survival times of untreated trigeminal
○ Lymph node aspirates nerve sheath tumors were 5-21 months.
Diagnostic Overview
A presumptive diagnosis can be made with TREATMENT PEARLS & CONSIDERATIONS
history, clinical signs, and diagnostic imaging;
cytologic or histopathologic evaluation is Treatment Overview Comments
required for definitive diagnosis. Complete tumor excision if possible and pain • Early diagnosis increases the potential for
relief are the desired goals; radiation therapy complete excision.
Differential Diagnosis can be used for palliation. • Orthopedic conditions typically do not
• Other soft-tissue tumors (e.g., fibrosarcoma, produce neurologic deficits; if proprioceptive
chondrosarcoma, lymphoma) can invade Acute General Treatment deficit or localized muscle atrophy is present,
or compress nerves and result in similar • Surgical exploratory/excision a nerve sheath tumor may be the cause.
neurologic deficits and imaging appearance. ○ Radical excision (i.e., limb amputation ± • Even advanced imaging may fail to identify
• Abscess, granuloma hemilaminectomy) provides the optimal the tumor if it is small or diffuse.
• Orthopedic abnormalities (e.g., osteoarthritis, chance of complete excision and is recom-
osteochondrosis desiccans [OCD], biceps mended in most cases. Technician Tips
tenosynovitis) • Radiation therapy • Chronic lameness with significant muscle
• Other cranial neuropathies (e.g., tumors of ○ Adjunctive to surgical excision atrophy should raise suspicion for a nerve
the brainstem or cavernous sinus) ○ Can be used as monotherapy in nonresect- sheath tumor.
• Other neuropathies (e.g., lateralized disk able cases • Patient can have paresthesia in the lame limb
herniation) • Adjunctive chemotherapy or in the axillary/inguinal regions.
• Traumatic brachial plexus injury ○ Rarely used as monotherapy
○ Doxorubicin, metronomic therapy Client Education
Initial Database • Clients should understand the potential for
• Neurologic exam (p. 1136) Chronic Treatment progression/recurrence.
• Radiographs of the affected limb to rule out • Analgesics • Clients should be counseled regarding
orthopedic conditions • Glucocorticoids may help alleviate some quality-of-life issues that pertain to their pets.
○ It is important to avoid overinterpreting discomfort and reduce peritumoral inflam-
the presence of osteoarthritis, which can mation; however, there is insufficient research SUGGESTED READING
be a concurrent condition and not the to support or refute their use for treating Brehm DM, et al: A retrospective evaluation of 51
primary cause of presentation. this condition. cases of peripheral nerve sheath tumors in the dog.
• Spinal radiographs may show subtle osteolysis J Am Anim Hosp Assoc 31:349-359, 1995.
at the vertebral foramen. Drug Interactions AUTHOR: David M. Brewer, DVM, DACVIM
• Concurrent administration of nonsteroidal
Advanced or Confirmatory Testing antiinflammatory drugs (NSAIDs) and EDITOR: Karen R. Muñana, DVM, MS, DACVIM
• Electrophysiologic studies (electromyography glucocorticoids is NOT recommended.
and motor nerve conduction velocity) • Other potential drug interactions depend on
○ Differentiate neurologic from orthopedic the specific therapeutic modalities chosen; cli-
conditions. nicians should consult appropriate references.

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