Pulse - January 2025 - 12

DIMENSIONS IN SURGERY + CRITICAL CARE
ANIMAL SPECIALTY & EMERGENCY CENTER
Surgical Management of a
Thyroglossal Duct Cystadenoma
in a Geriatric Dog:
A Novel Congenital Anomaly
Dillon Scott, DVM, Surgery Intern
A
13-year-old
spayed
female terrier-mix presented
to the VCA Animal
Specialty and Emergency
Center (ASEC) for evaluation
of a 3-month history of
progressive coughing identified
during routine oncologic
surveillance through the
ASEC Medical Oncology Service
following treatment for
malignant melanoma.
The patient's medical history included
mammary ductular
adenocarcinoma,
small cell gastrointestinal lymphoma, tracheal
and mainstem bronchial collapse,
degenerative mitral valve disease with tricuspid
regurgitation (ACVIM Stage B2)1,
hepatomegaly, and progressive elevation
in alkaline phosphatase (ALP). Previous
oncologic treatment included Oncept
Canine Melanoma Vaccine administration
and chemotherapy with cyclophosphamide
(55 mg PO, 8 treatments) and 5-fluorouracil
(150 mg/m², 8 treatments).
Five months prior to presentation,
orthogonal screening chest radiographs
revealed a newly identified soft tissue
opacity within the mediastinum associated
with a decreased right cranial lung
lobe volume. It was elected to monitor this
change with conservative management of
the cough using hydrocodone syrup as
prescribed by the referring veterinarian.
Upon presentation, the patient exhibited
stable vital signs but had an intermittent
dry hacking cough, concerning for progressive
mitral valve disease versus historic
mainstem bronchial and tracheal collapse.
12
Physical examination revealed a grade 3/6
left apical systolic heart murmur, a 2 x 4
cm mass of the right 5th mammary gland
and an 8 mm pigmented dermal mass
located on the cranial ventral neck at midline.
An in-house complete blood count
and biochemistry (Abaxis) showed a historic
elevated ALP at 609 U/L (reference
range: 20-150 U/L) and glucose at 121
mg/dL (reference range: 60-110 mg/dL).
Differential diagnoses included structural
or functional cholestasis and hyperadrenocorticism.
An echocardiogram was
recommended due to the persistent and
worsening cough, which revealed static
heart disease and the presence of a large
cranial mediastinal mass likely not associated
with the heart. Orthogonal thoracic
radiographs were recommended and confirmed
a large progressive homogeneous
soft tissue opacity occupying the right
cranial thorax, prompting the recommendation
for advanced thoracic imaging. The
patient was discharged with hydrocodone
(2.5-5mg PO q8-12hr) and maropitant
(12mg PO q24h) to manage the cough,
and an outpatient contrast-enhanced
computed tomography (CT) scan was
scheduled two weeks after the initial
presentation. A CT scan was performed
under general anesthesia; premedication
included maropitant (1 mg/kg IV) and
butorphanol (0.2 mg/kg IV) followed
by co-induction using propofol (3 mg/kg
IV) and midazolam (0.3 mg/kg IV) to
effect, with isoflurane maintenance and
positive pressure ventilation. A singlephase,
iodinated contrast scan was also
performed using Omnipaque (400mg/kg
IV). The CT scan revealed a well-defined
4.8 cm x 2.7 cm poorly contrast-enhancing
soft-tissue attenuating mass within the
right cranial mediastinum consistent with
radiographs. No evidence of metastasis or
adjacent tissue involvement was appreciated.
An ultrasound-guided fine-needle
aspiration was performed immediately
following the CT scan to further characterize
the mass as neoplastic vs benign
before additional recommendations were
made. Cytology demonstrated a cystic
epithelial tumor with abundant degenerating
fluid and mixed inflammation likely
less concerning for overt malignant neoplasia.
Over the following three weeks,
the patient's cough worsened and became
resistant to treatment with hydrocodone
and maropitant. Following discussions
with the owner about the diagnostic findings
and the patient's declining quality
of life, likely attributed to the worsening
cough, the decision was made to proceed
with an elective exploratory thoracotomy.
The patient was placed under general
anesthesia, which included a fentanyl
constant rate infusion (5 µg/kg/hr), followed
by co-induction with propofol (3
mg/kg IV) and midazolam (0.3 mg/kg
IV) to effect, and isoflurane maintenance.
Maropitant (1mg/kg IV) and ampicillin/
sulbactam (30 mg/kg IV) were administered
at induction. The patient was placed
in dorsal recumbency, and the ventral thorax
was clipped and aseptically prepared.
A standard median sternotomy was performed,
and the pleura and mediastinal
attachments were dissected using monopolar
electrocautery, Ligasure® and sharp
dissection, revealing an approximately 5
x 3 cm light pink mass with an associated
cystic structure containing approximately
10ml of dark brown non-viscous fluid.
JANUARY 2025
PULSE
Pulse - January 2025

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