SOFT TISSUE SURGERY

4.1 Patagium

The patagial membranes of bats and gliders are prone to injury, particularly when entangled in barbed wire fences, and in the case of bats, entanglement in fruit netting and electrocution (Johnson and Hemsley 2008; Olsson and Woods 2008; Chapter 42).

In gliders, patagial injuries that interfere with function (large marginal tears, large holes or when avulsed from the fore- or hindlimb attachments) may be surgically repaired with absorbable subcuticular sutures. They are more likely to chew out exposed skin sutures. The dorsal and ventral membrane skin must be sutured separately in two layers. Wound contracture is common, may necessitate additional resection and may render the glider non-releasable (Johnson and Hemsley 2008).

Special considerations for the repair of bat wing mem­brane injuries include:

• Chlorhexidine solution is less irritating to the sensitive wing membrane than iodine or alcohol preparations (Heard 2003).

• Repair is complicated by wound contraction, dehis­cence and easily damaged vasculature (Olsson and Woods 2008).

• Following entanglement or electrocution, it may take up to 1 wk for devitalised wing membrane to become apparent. Delay debridement until the full extent of the injury is evident, when tissue is dry (see Chapter 42).

• Circular defects with intact margins usually heal une­ventfully if less than 3-4 cm (R Booth pers. comm.). Larger defects often contract to become smaller over time and may not impede flight. Very large defects that impede flight are an indication for euthanasia (S Frith pers. comm.).

• If devitalisation of tissue is advanced and scabbed over, allowing the tissue to repair without treatment is often successful.

• Wing wounds have been managed successfully with Tegaderm™ Film dressing. It is well tolerated by bats and preferably placed on the outside of the wing where they groom less (S Frith pers.

• Bats will often fastidiously lick and chew at wounds that have been dressed, sutured or topically medicated. Elizabethan collars have been used successfully to manage this (Olsson and Woods 2008).

4.2 Ophthalmic surgery

4.2.1 Tarsorrhaphy

Tarsorrhaphy is useful for treatment of corneal ulceration as it replaces the need for frequent restraint while apply­ing topical medication. Tarsorrhaphy has been success­fully used to treat corneal ulceration in a tammar wallaby (N. eugenii) with an atrophied nictitans (Lecu et al. 2008).

4.2.2 Cataract surgery

Cataract surgery in Australian mammals has primarily been performed in macropods. Cataracts are most com­monly seen in PY (either free-ranging or hand-reared), the aetiology of which remains poorly understood (Vogelnest and Portas 2008). Cataract surgery in macropods is technically straightforward: neuromus­cular relaxants are not required, pupils dilate well with 1% tropicamide and lenses can often be removed by phacoemulsification. However, intra- and postoperative complications are common and include retinal detach­ment and/or glaucoma, resulting in irreparable blind­ness and possibly pain necessitating globe evisceration, enucleation or euthanasia (Stanley 2002; K Caruso pers. comm.).

In PY, surgical removal of the lens often reveals extensive opacification of the vitreous, potentially a poor prognosis for return to normal vision. Historically, because of this complication, cataract surgery in macro­pod PY was not recommended (Stanley 2002). However, routine cataract surgery is now being performed in hand-reared eastern grey kangaroo (Macropus gigan- teus) PY or juveniles. The addition of a posterior capsu- lorhexis, extensive vitrectomy and 4-6 mg triamcinolone placed into the posterior chamber has reduced the inci­dence of retinal detachment and secondary glaucoma, with ~60% of cases returning to normal vision (K Caruso pers.

Cataracts are often seen in pinnipeds in zoos and oceanariums (Barnes et al. 2008; Colitz et al. 2010; see Chapter 45). Most cataracts progress to cause visual impairment, and are at risk of anterior luxation with associated pain, and luxation-induced corneal fibrosis and oedema. Early lensectomy may be indicated to pre­vent this. Lensectomy, with appropriate perioperative and postoperative medical management, results in pain relief and improved vision in pinnipeds with lens luxation and cataracts (Colitz et al. 2010). Intracapsular or extracapsular lens extraction techniques were favoured by Colitz et al. (2010), as the round, relatively rigid lens of pinnipeds can make phacoemulsification difficult. However, phacofragmentation and phacoemul­sification have been successfully used to remove pin­niped cataracts in younger animals (Barnes and Smith 2004; Esson et al. 2015). Intravenous atracurium or other non-depolarising medications are used to achieve a motionless eye with a central gaze during surgery (C Colitz pers. comm.). Overall, surgical removal of the lenses has proven successful. The best results have been in eyes that did not have chronic anterior lens luxations and did not have medial strabismus.

4.2.3 Corneal surgery

Corneal ulceration and chronic keratopathy are not uncommon in pinnipeds and cetaceans in zoos and oceanariums (Blyde and Vogelnest 2008; Barnes et al.

4.2.4 Conjunctival ablation

Conjunctival ablation may be indicated in koalas with chronic chlamydial conjunctivitis where the proliferative conjunctiva obscures vision. The third eyelid is grasped with forceps and exposed conjunctival tissue is trimmed. For palpebral conjunctivae, the eyelid is rolled outward, lifted away from the globe and excess tissue is trimmed (Blanshard and Bodley 2008).

4.2.5 Enucleation

Enucleation is an option for painful non-healing eyes. Standard domestic species techniques are applicable. A koala with anterior chamber collapse, buphthalmos and keratitis underwent transpalpebral enucleation and a haemostatic sponge was placed within the orbit before skin closure (Liddle et al. 2014). Enucleation has been performed in many other Australian mammals in man­aged care, including a long-nosed fur seal (Arctocephalus forsteri) with traumatic eye injury from a smalltooth cookiecutter shark (Isistius brasiliensis) bite (L Vogelnest pers. comm.) and a red kangaroo with panophthalmitis associated with a retrobulbar abscess (M Campbell­Ward pers. comm.).

4.3 Abdominal surgery

4.3.1. Laparotomy and laparoscopy

In male marsupials, access to the entire abdomen is rela­tively straight forward; however, in females, access to the caudal abdomen is complicated by the presence of the pouch, PY or engorged mammae within the pouch. If the pouch is empty an incision can be made within the pouch to access the caudal abdomen. If a PY is present, but no longer permanently attached to a teat, it can be removed before surgery; however, consideration may need to be given to hand-rearing, as replacing it in the pouch postoperatively may impede wound healing and/ or cause discomfort for the dam.

Abdominal surgery in pinnipeds is complicated by their abdominal wall anatomy (Table 10.1) and potential for poor postoperative healing in an aquatic environment. Dry-docking and limiting activity for several days postop- eratively may be indicated in some cases (Barnes et al. 2008). However, early access to water may also reduce post­operative anxiety, pain and discomfort from abrasion of the incision site (Higgins and Hendrickson 2013; L Vogel- nest pers.

In cetaceans, surgical access to the abdomen is limited, large surgical wound healing is poor and cetaceans must be maintained in water (Blyde and Vogelnest 2008; Hig­gins and Hendrickson 2013). Accordingly, abdominal surgery is best performed using keyhole laparoscopic techniques in which the small incisions increase the like­lihood of watertight closure (McBain 2001; Higgins and Hendrickson 2013). Liver and enteric biopsies can be obtained, often with ultrasound guidance. Rosenberg et al. (2017) describe an emergency exploratory laparotomy in a white-sided dolphin (Lagenorhynchus obliquidens) with severe enteritis and peritonitis. The abdomen was accessed through an 18 cm left ventrolateral flank inci­sion through skin, blubber muscle and peritoneum. Clo­sure included three suture layers in the abdominal wall muscle and one tension-relieving layer through skin and blubber. Although the animal died 3 d postoperatively from sepsis, this attempt demonstrates that large surgical procedures are possible in cetaceans.

4.3.2 Gastrointestinal surgery

a. Oesophageal diverticula

Oesophageal diverticula have been surgically corrected in parma wallabies (N. parma). A ventral midline cervical incision exposed the diverticulum. The dilated oesopha­geal tissue was excised and the oesophagus sutured in two simple interrupted layers (Okeson et al. 2009).

b. Mesenteric volvulus

Mesentric volvulus occurs with some frequency in macropods (Chapter 31). It is often acute and diagnosed postmortem. If diagnosed antemortem, emergency surgi­cal correction may be attempted, but prognosis is poor and recurrence and postoperative complications are common. Varying degrees of rotation (typically 180°) and discolouration of tissue can occur. The volvulus must be de-rotated and the intestines and involved organs assessed for vascular compromise. Gastropexy can be performed to prevent recurrence. Mesenteric volvulus and gastric dilatation-volvulus have been surgically cor-

Fig. 10.2. Lateral radiograph of brush-tailed rock-wallaby (Petrogalepenicillata) with mesenteric volvulus. Note the cranially displaced small intestines (arrow). Image: Taronga Wildlife Hospital

Fig. 10.3. Pharyngostomy tube placement in a northern nail-tailed wallaby (Onychogalea unguifera). An 18F feeding tube was placed, extending to the caudal oesophagus (verified radiographically). The tube was secured in place using a purse string, Chinese finger trap suture and single skin suture to the lateral neck. Photo: Larry Vogelnest

rected in several macropods, including a red kangaroo that was euthanased 3 mo later because of anaemia (Knafo et al. 2014), a western grey kangaroo (M. fuligino- sus) that had recurrent volvulus and was euthanased (J Weller pers. comm.) and a brush-tailed rock-wallaby (Petrogalepenicillata) that died during surgery (Fig. 10.2).

Gastrointestinal torsions and intussusception in koalas have been surgically corrected with limited suc­cess. Mesenteric root torsions ranging from 360 to 1260° have been reported in koalas with colic and/or acute abdominal distension. Torsions were associated with a gas-distended caecum or congested small intestines. Tor­sions were de-rotated and tissues appeared viable. One koala required resection and anastomosis of devitalised jejunum 2 wk later and died postoperatively. Another required surgical repair of recurrent colic and was later euthanased because of cryptococcosis with no evidence of recurrent torsion. The third showed no recurrence of clinical signs 14 m after surgery (Joyce-Zuniga et al. 2014).

c. Resection and anastomosis

In koalas, resection and anastomosis can be performed on traumatised small intestine or colon. The caecal wall is very fragile and must be handled with extreme care. Par­tial-thickness caecal tears can be gently oversewn. Resec­tion and anastomosis of the caecum may be performed with double-layer closure, but lumen space is typically reduced (up to 50% reduction is usually tolerated). Inflammation and ileus in the remaining caecum is often a problem (A Gillett pers. comm.). Healthy margins and meticulous surgical technique are important to minimise the risk of wound breakdown.

d. Gastrointestinal foreign bodies

Gastrointestinal foreign bodies occur occasionally in hand-reared macropods, secondary to trichophagia or ingestion of non-food items (Portas pers. comm.). The sur­gical approach for corrective gastrotomy or enterotomy will depend on the location of the obstruction. Surgical management of an intestinal trichophytobezoar in a red­necked wallaby has been described (Minor et al. 2023).

e. Placement of feeding tubes

Pharyngostomy and oesophagostomy tubes have been used successfully in marsupials. Standard techniques for domestic animals are used (Fig. 10.3).

Gastrostomy tubes have been used in several koalas that were unable to eat because of jaw or pharyngeal inju­ries or anorexia secondary to other diseases. Pharyngos- tomy tubes block easily with blended leaves and have been associated with reflux and regurgitation. Gastric feeding tubes may be more suitable for feeding large vol­umes of blended eucalyptus leaves. The stomach is accessed through a ventral midline incision. A small inci­sion is made in the left dorsolateral aspect of the stomach

wall and the cuffed end of a sterile size 6-8 endotracheal tube is passed into the stomach. A purse string suture is used to close the stomach around the tube and the cuff is inflated. The remainder of the tube is passed through the left lateral side of the abdominal body wall, a gastropexy performed and the tube secured to the skin with a finger trap suture (A Gillett unpublished).

An alternative to open surgical gastrotomy in koalas is placement of a feeding tube via percutaneous endoscopic gastrostomy (PEG), using a technique adapted from those described for domestic small animals (C Singleton unpublished).

These techniques have been used in a small number of koalas with mixed results. Complications include the tube pulling out, cuff deflation, tube blockage, surgical site infection, leakage of stomach contents, ileus, dysbiosis and typhlocolitis (A Gillett and C Singleton pers. comm.).

4.3.3 Cystotomy

Cystotomy is performed using a similar technique to that in dogs and cats. Indications include removal of stones and, in koalas with cystitis, post-treatment removal of inflammatory debris (A Gillett pers. comm.)

4.4 Excisional procedures

Neoplastic masses and fungal or parasitic granulomas are common indications for excisional procedures. Standard surgical techniques generally apply. Surgical excision or debulking of fibrous, proliferative and infiltrative masses associated with sparganosis in short-beaked echidnas may be attempted if not too advanced (Middleton 2008).

For large, neoplastic mammary masses in marsupials with shallow pouches, partial or complete pouch ablation may be required to ensure complete excision with wide margins (Figs 10.4 and 10.5). For total pouch ablation an elliptical incision is made just peripheral to the pouch lips from the cranial to the caudal extremities of the pouch. The entire pouch is bluntly dissected away from the body wall, inclusive of the mammae, ligating vessels as needed. Dead space must be closed to avoid postoperative seroma. The incision is closed in the midline (L Vogelnest pers. comm.).

Surgical treatment of haemangiosarcoma and mam­mary carcinoma has been successfully performed in sugar gliders (Petaurus breviceps). A sugar glider was diagnosed with dermal haemangiosarcoma on the margin of the patagium. Surgical excision was performed using radio­surgery to incise both layers of the patagium and excise the tumour with adequate tissue margin. The glider

Fig. 10.4. (a) Bilateral complex carcinoma and papillary cystadenomas of the mammary glands in a Tasmanian devil (Sarcophilus harrisii). (b) After total pouch ablation 4 wk postoperatively. Photos: Larry Vogelnest

Fig. 10.5. (a) Adenomyoepithelioma in an eastern ring-tailed possum (Pseudocheirusperegrinus). (b) Excision with partial pouch ablation. One month later a contralateral mammary nodule was noted to be present and growing and the remaining portion of the pouch was ablated. Photos: Larry Vogelnest

remained clear of recurrence at the 1-yr postoperative examination (Rivas et al. 2014). In a female sugar glider, an anaplastic mammary carcinoma was removed from the

right mammary gland. The skin was incised using radio­surgery and the vascular mass was removed, requiring ~50% pouch resection. Postoperative radiation of the sur­gical site was performed to prevent recurrence. The glider was euthanased 10 d later because of self-mutilation but the surgical site appeared to be healing (Keller et al. 2014).

Nasal masses in koalas include cryptococcal granulo­mas, polyps, adenocarcinoma and osteochondromatosis (see Chapters 18, 25 and 32). The surgical approach to a nasal mass in the koala will vary according to its location. Consideration should be given to the thin nasal septum, confined space and simple conchae of the nasal cavities. Bercier et al. (2012) describe the surgical excision of a tumour of spindle-cell proliferation (spindle-cell tumour or nasal polyp) in the nasal passage conchae that was deviating the nasal septum. Wynne et al. (2012) describe surgical removal and medical treatment of a cryptococcal granuloma extending from the caudal nasal cavity to the ethmoid turbinates and ventrally to the nasopharynx.

4.5 Tracheostomy

Emergency temporary tracheostomies have been per­formed in two juvenile eastern grey kangaroos to relieve traumatic upper airway obstruction and acute respiratory distress (Fig. 10.6). A ventral midline skin incision was made in the cervical region distal to the traumatised area and the sternohyoid muscles were separated. A transverse tracheotomy (one-third of the tracheal circumference) was made through an annular ligament and an endotra­cheal tube was inserted into the trachea, immediately alleviating the obstructive dyspnoea. The tube was secured to the adjacent sternohyoid muscles with a Chi­nese finger trap suture and the skin was closed on either side of the tube. The tubes were well tolerated by the kan­garoos and maintained their patency. One kangaroo was euthanased 4 d postoperatively because of persistent laryngeal dysfunction. The other had the tube removed after 5 d; a light dressing was applied to the neck for 48 hr and the wound healed by second intention; this animal made a full recovery (M Campbell-Ward pers. comm.).

5.