Saturday, December 11, 2010

271. 4th surgery to remove cheek tumour in an old dog

Report is written by a 4th year vet student from Murdoch Univ doing internship at Toa Payoh Vets. I welcome different perspectives from interns.


Surgery Report for XXX (11 Y/O mixed breed male dog)
PRE-OP
History:
XXX was presented with a malignant tumour on the Right cheek. Tumour was persistent, with ill-defined margins and had a rough 7cm circumference. It also had a history of dermatitis with multi-focal exudative pustules and papules located primarily on the proximal fore and hindlimbs, with severe scaly and crusted regions of epidermis on the caudal elbow and knee joints. XXX was otherwise eating normally.

Physical Exam (PRE-OP):
On physical examination, XXX displayed an obdunted attitude. Heart, respiratory rate and temperature were within normal limits at 102 bpm, 30bpm and 39.2degrees Celsius respectively. Peripheral perfusion seemed normal with mucous membranes being moist and pink and CRT < 2 secs. Breath was malodorous (possibility of bacterial / fungal overgrowth inside the mouth).

Treatment Plan:
Palliative and curative.
To surgically excise the malignant cheek tumour via electrocautery and check for observable metastasis to regional lymph nodes under general anaesthesia.

OPERATION
Surgical and Anaesthetic details:
XXX was not sedated prior to anaesthetic induction as there was sufficient restraint to hold him down.
Catheterization was performed via a 22G needle into his left cephalic vein for easy intravenous (IV) access before anaesthetic induction with Diazepam (0.4ml) and Ketamine (0.4ml) totaling 0.8ml IV. Roy was deemed sufficiently induced after 10minutes and surgery proceeded. Surgical site was prepped with chlorhexidine and alcohol and a transverse incision across the tumour was made via electrocautery.
The epidermis above the tumour site was undermined to relieve skin tension and provide easier excision of the tumour itself. Roy was also given an IV drip of 5% dextrose wit 0.45% NaCl to compensate for electrolyte losses and to prevent dehydration and hypovolaemia.
Care was taken not to sever the facial nerve although part of it might have been as the tumour margins were large and irregular and the base of the tumour was located deep within the facial cavity, thus requiring aggressive surgical therapy. Upon tumour excision, tumour was found to have metastasized to the bone as well as the upper gingiva. As the effects of the induction drugs weared off, gaseous anaesthesia for maintenance was administered. 5% isoflurane was administered initially and slowly decreased over the course of the surgery up to 0.2% during the muscle, subcutaneous and skin closure at the excision site. 0.1% zoletil was also administered IV during the course of the surgery as Roy was still deemed too light. After 40 minutes, tumour was partially resected and wound closure commenced so as to decrease anaesthetic risk and toxicity. Muscle, subcutaneous and skin closure was performed using 2-0 synthetic polysorb, absorbable suture for all layers. Muscle and subcutaneous layers were closed using a simple interrupted pattern while the skin layer was closed using a mattress suture pattern.

POST-OPERATION
Surgical site was washed and swiped clean with sterile saline to reduce risk of sepsis and 1ml of Tolfenamic Acid (Tolfedine) was administered IV as post-op analgesia. XXX was then placed back in his cage and equipped with an E-collar while he continued to receive the remainder of the 5% dextrose and 0.45% NaCl at maintenance rates followed by another 500ml of Hartmann’s after, also at maintenance flow rates to prevent dehydration, hypovolaemia and to maintain electrolyte balance. Blood sample was taken for CBC and biochemistry while a tumour sample was also submitted to QuestLabs for histopathology.

DRUGS USED AND PRECAUTIONS
Ketamine:
- Mode of action: Acts at the N-methyl-D-Aspartic (NMDA) receptors and blocks central sensitization. It is useful for patients with chronic pains and patients that fail to respond to conventional analgesic therapy. Can also be used (mostly in combination with other drugs such as Xylazine and Diazepam) for sedation and anaesthetic induction.
- Precautions: AVOID the use of ketamine in patients with traumatic head injury as it increases cerebral blood flow and may increase intra-cranial pressure.
Diazepam:
- Mode of action: Diazepam is a benzodiazepine that binds to a specific subunit on the gamma-aminobutyric acid (GABA) receptor at a site distinct from the binding site of the endogenous GABA molecule. Therefore it works as an allosteric modulator of GABA, enhancing its effects and provides good anxiolytic, anti-convulsant, hypnotic and amnestic properties. Used especially in the management of seizure cases.
- Precautions: IV administration of diazepam should be performed slowly, particularly when injected into the smaller veins such as the cephalic vein because of the potential of thrombophlebitis and cardiotoxicity due to the propylene glycol base.
Diazepam may cause weakness, drowsiness and loss of motor coordination. In rare cases, it may result in paradoxical excitement, unexpected aggression or unusual behavourial changes.
Zoletil
- Mode of action: Combination of 2 drugs, tiletamine and zolazepam. Tiletamine’s mode of action is similar to that of ketamine as it is a NMDA receptor antagonist and blocks central sensitization as well. Zolazepam’s mode of action is similar to diazepam as it is a pyrazolodiazepinone derivative that is structurally similar to the benzodiazepine drugs.
- Precautions: Contraindicated in animals with CNS signs, hyperthyroidism, cardiac disease, pancreatic or renal disease, pregnancy, glaucoma or penetrating eye injuries.

REFLECTIONS
As tumour was incompletely resected, the chance of recurrence is very high. Prognosis of this dog is very poor as well as it is old and there has already been evident local metastasis to bone and gingival. Distant metastasis has not been diagnosed but is possible, which will further decrease its prognosis for survival.
In my opinion, if cost is not an issue for the client, I would recommend palliative treatment with NSAIDs such as acetaminophen, aspirin, meloxicam as well as prophylactic broad spectrum antibiotics such as Trimethoprim Sulphate (TMS) or Amoxicillin Clavulanate (Amoxy-clav) along with neoplasia excision again when the tumour grows again to a clinically significant size.
As the surgery had to be aggressive, part of the facial nerve might have been severed in the process which might have resulted in the post-op excessive salivation, drooping of the lip and ear on the ipsilateral side of the lesion. Dog should also be examined for signs of nystagmus, head tilt, asymmetrical pupil size dropping of food and ataxia to further confirm the suspicion of facial nerve paresis or paralysis. Part of the sublingual and mandibular salivary glands and/or their ducts might have also been severed in the process, resulting in excessive salivation. Due to traumatic injury to the glands and/or ducts, in my opinion, I would expect the dog to develop a sialocele which would then require further surgical intervention. Diagosis of this could be confirmed with fine needle aspirate should a SOFT, palpable mass develop near the mouth region. Needle aspirate can also help differentiate a sialocele from a neoplastic process.
On a separate note, the dermatological processes should also be looked into if the client is willing. Punch biopsies should be done on the pustules and papules, centered in the middle of the biopsy specimen. Punch biopsies should also be obtained from the scaly and crusted areas AS WELL AS from the normal skin. This is to allow comparisons of the epidermis and stratum corneum of the 2 sites by the pathologist. This is done to diagnose the nature of the skin lesions and to determine an appropriate treatment plan for XXX with systemic treatment such as injectable or oral cephalosporins, enrofloxacin etc. Adjunctive therapy could include topical treatments such as Chlorhexidine gluconate (Pyohex Dermcare) shampoos as well as benzoyl peroxide (Pyoben Virbac)


Done by:
Name of student

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