VetWrap Spring 2013 - DoveLewis | Emergency Animal Hospital

Figure 1. Lizzy, pre-op, with a 10 x 14 cm irregular, ovoid, soft
tissue mass associated with the right antebrachium.
Figure 3. An ovoid skin incision was made around the base of the
mass, preserving grossly normal medial and lateral skin.
Figure 4. The mass originated from an irregular pedicle about 3 cm in
length starting from the deep fascia between the extensor carpi radialis
and digital extensor muscle bellies.
CAse Study
Surgical Debulking of a Large
Peripheral Nerve Sheath Tumor
Ashley A. Magee, DVM, DACVS
Lizzy, a 13-year-old spayed, female
retriever mix, presented to DoveLewis’
surgery department for evaluation and
possible removal of a large tumor on
the right forelimb. She was diagnosed
with a peripheral nerve sheath tumor
approximately 18 months prior via incisional
biopsy. The histopathology report
characterized the malignant neoplasm
as relatively low grade. No treatment was
elected at that time. From diagnosis to
presentation to DoveLewis, the mass
grew considerably and the skin had
become irritated and thin, and Lizzy had
begun to lick at the mass. A consultation
with an oncologist had been pursued
and surgical debulking recommended
since amputation was not considered
an option by Lizzy’s owners due to good
function of the limb, age, and lifestyle
considerations (she lives on a houseboat).
On examination, Lizzy was bright and
alert with a normal physical examination
other than a 10 x 14 cm irregular, ovoid,
soft tissue mass associated with the right
antebrachium (figure 1). The central 5 cm
of skin was erythematous, partially ulcerated,
and painful to palpation. No lameness
was noted. Recent CB, serum chemistry,
urinalysis and three view thoracic radiographs
were within normal limits.
After discussing their options and the
potential complications (failure to heal,
rapid regrowth of the mass, neurovascular
complications and anesthetic risks) of
debulking surgery, the clients decided to
go forward with the procedure. Lizzy was
admitted to the hospital for surgery. An
intravenous catheter was placed and she
was started on 5 ml/kg isotonic fluids
presurgically. Standard premedication
with hydromorphone 0.1 mg/kg and midazolam
0.2 mg/kg was given IV, along
with a perioperative dose of cefazolin IV
at 30 mg/kg. Preoxygenation was started
and pulse oximetry and electrocardiographic
monitoring begun prior to induction.
Lizzy was induced with propofol 5 mg/kg IV
to effect, intubated and placed on isoflurane
in oxygen for maintenance. Fluids were
increased to 10 ml/kg/hr. Lizzy was placed
in dorsal recumbency and a hanging limb
prep performed (figure 2). A brachial plexus
block was performed in standard fashion
using 2 mg/kg lidocaine and 0.5 mg/kg
bupivicaine for supplemental analgesia. The
patient was moved into the OR for surgery.
An ovoid skin incision was made around
the base of the mass, preserving grossly
normal medial and lateral skin (figure 3).
Hemorrhage was controlled with electrocautery
and ligation where appropriate. Sharp
Figure 2. Lizzy was placed in dorsal
recumbency and a hanging limb prep
performed.
dissection was used to free the mass from
underlying subcutis and fascia, ligating
larger vessels with 3-0 polyglyconate. The
mass originated from an irregular pedicle
about 3 cm in length starting from the deep
fascia between the extensor carpi radialis
and digital extensor muscle bellies (figure 4).
The pedicle and mass with attached fascia
and skin were removed en bloc and residual
grossly abnormal tissue removed. The area
was lavaged with a liter of warm saline then
gloves and instruments changed. The large
size and weight of the mass had effectively
stretched the surrounding skin to the point
that tension free longitudinal closure could
be performed with undermining alone. The
subcuticular layers were closed using 3-0
Maxon in a simple interrupted pattern. Skin
was closed with 2-0 polypropylene in a
simple continuous pattern. The limb was
placed in a soft padded bandage. The clients
declined submission of the mass for evaluation
of the tumor margins.
Lizzy recovered quickly and uneventfully from
surgery and was discharged to her owners
later that evening with oral pain medications
(tramadol and gabapentin). She was
rechecked at 48 hours, one week, and two
weeks post-operatively. The surgical wound
healed normally and Lizzy did not experience
any complications. Follow-up seven months
post-operatively revealed Lizzy had no gross
evidence of tumor regrowth and was otherwise
normal (figure 5).
Peripheral nerve sheath tumors are masses
arising from nervous tissue; the specific cell
origin is often not identifiable. They have variable
histologic characteristics of malignancy,
but often cause considerable local invasion
and have a low rate of distant metastasis. The
thoracic limbs are more commonly affected
in dogs. If associated proximally with a nerve
root, lameness is characteristic, but when
located more peripherally on the limb, lameness
may not be part of the clinical problem.
When associated with the spinal column,
lameness, muscle atrophy, and significant
neurologic dysfunction are often present.
When associated with a major motor nerve
such as the radial nerve, limb weakness or
dysfunction may be present before or after
resection of the mass.
Treatment consists of resection of the tumor
with wide margins. Amputation is often
required to obtain adequate margins and
due to resection of motor nerves to the limb
along with the tumor, making the limb nonfunctional.
In Lizzy’s case, amputation was
not considered a good option by her owners.
Because the mass was causing no neurologic
dysfunction, was located distally on the limb
below the major nerve trunks, and no metastasis
was detected on presurgical screening,
debulking was considered reasonable to
obtain significant palliation of the disease.
Residual neurovascular dysfunction was
discussed as a potential complication of the
surgery, along with wound healing complications
and aggressive return of the tumor.
These complications and the potential need
for later amputation or euthanasia should
complications be severe, should be discussed
with clients prior to performing palliative
debulking of a peripheral limb tumor.
Lizzy’s procedure was successful for several
reasons. At surgery, no direct association
with a major nerve trunk was found and
forelimb musculature was not invaded, leaving
these structures intact and preserving
her limb function. Similarly, the cephalic
vein and radial and median vasculature was
preserved, allowing for retained circulation to
the surgical site and optimal environment for
healing. The ability to obtain primary closure
of the wound was of
significant benefit;
the skin stretching
effect of the mass
provided grossly
normal skin for closure.
Skin stretching
techniques such
as presuturing for
several days prior to
surgery or creation of
a transposition flap
from brachial skin at
surgery are relatively
simple techniques
that could be
employed to help
create a tension-free
wound closure when
adequate skin is not
available.
In summary, tumor debulking can be
rewarding in select cases and patients
can have a satisfactory tumor-free interval
when more aggressive surgical methods
are not appropriate or desired by the client.
Tumor type, location and patient specifics
should be evaluated together to determine
the likelihood for success, and clients
should be well educated in the risks and
potential pitfalls of the procedure.
We would like to thank Lizzy’s owners
for allowing us to share her story, and the
Veterinary Cancer Referral Center and
Laurelhurst Veterinary Hospital for referral
of this patient. •
Figure 5. Lizzy, seven months post-op.
Suggested Reading:
Kent, M and Northrup, N. Nerve sheath
tumors. In Tobias, KM, Johnston, SA, eds.
Veterinary Surgery: Small Animal Vol 1 pp
547-548. Saunders, 2012
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10 VetWrap Volume 7 Issue 2 Spring 2013
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