Use of a masseter fascia transposition flap for ventral orbital stabilization after partial inferior orbitectomy in a dog

Abstract

A 12-year-old neutered male pit bull crossbreed dog was presented because of a right caudal maxillary swelling. Computed tomographic imaging of the skull and revealed a right maxillary mass with lysis of the medial wall of the right orbit and rostral aspect of the zygomatic bone. A biopsy was done, and histopathology results were consistent with a mixed odontogenic tumor. The mass was resected with a caudal maxillectomy and partial inferior orbitectomy with 1-centimeter lateral margins. A transposition flap of the masseter fascia was performed to stabilize the globe. The cosmetic and functional outcomes were excellent during an in-person clinical examination 2 wk postoperatively and at a follow-up 1 y postoperatively (telephone communication with the owner).

Key clinical message:

The use of the masseter fascia as a transposition flap after a caudal maxillectomy and partial inferior orbitectomy proved successful for orbital stabilization in a dog.

Oral tumors are common in dogs and account for 6% of all canine neoplasia (1). The most common oral tumor types include malignant melanoma, squamous cell carcinoma, fibrosarcoma, osteosarcoma, acanthomatous ameloblastoma, and peripheral odontogenic fibroma (2). Surgery with wide surgical margins is the treatment of choice for most oral tumors (3). Caudally located tumors may require caudal maxillectomy and partial orbitectomy to ensure tumor-free margins (4). However, the latter procedure can result in a ventral defect of the orbit that may compromise orbital stability (5). Inappropriate stabilization of orbital contents may lead to complications such as enophthalmos, strabismus, traumatic uveitis, chronic epiphora, diplopia, optical nerve damage, or globe rupture (4,6).

Flaps are divided into 3 categories: free flaps, regional flaps, and local flaps (7). In the latter, adjacent tissue is transferred into the wound (7). Local flaps can be divided into 3 categories based on the type of primary movement required for transfer: advancement, rotation, and transposition (7). A rotational flap is a sliding flap in which a semicircle is created adjacent to the border of the defect and rotated to cover it (8). A transposition flap is a lifting flap in which a rectangular pedicle graft located 45 to 90° to the long axis of the defect is used to cover the wound (8).

In veterinary medicine, several techniques have been described for reconstruction of the ventral orbital rim. The temporalis fascia transposition flap (9), titaniummesh reconstruction (6), sling suture (10), orthopedic wire with polypropylene mesh (11), and 3D-printed polyprolactone/β-TCP scaffold (12) have been reported. Sivagurunathan et al (4) described the use of the masseter muscle as a rotational flap for obliteration of a small segmental defect at the level of zygomatic arch in a dog. However, when used as a rotational flap, this application lacks flexibility and is limited to small resections. The present report describes the use of the masseter fascia as a transposition flap to stabilize the globe after caudal maxillectomy and partial inferior orbitectomy in a dog.

CASE DESCRIPTION

A 12-year-old neutered male pit bull crossbreed dog weighing 41.3 kg was presented because of a right caudal maxillary swelling of 5 mo duration. The owner reported the dog appeared in pain when opening its mouth widely.

Upon physical examination, a solitary, 7 × 7 cm, firm, caudal maxillary mass was noticed extending to the level of the zygomatic arch. The right mandibular lymph node was moderately enlarged. Ophthalmic examination revealed mild enophthalmos. Hematologic and serum biochemical examinations were unremarkable.

Computed tomographic scans of the skull and thorax were obtained. The dog was premedicated with dexmedetomidine, induced with propofol, and maintained with inhalant isoflurane in oxygen. Pre- and post-IV administration of 60 mL (300 mg/mL) nonionic iodinated contrast material acquisitions revealed an extensive, multicystic, lobulated, partially mineralized mass measuring 7.3 × 6.4 × 7 cm, centered on the right maxilla. The mass was associated with regional bone lysis of the right maxillary bone, from the level of the right maxillary 3rd premolar tooth (107) to the right maxillary 2nd molar tooth (110); and with lysis of the rostral aspect of the right zygomatic bone. The mass invaded the ventrolateral aspect of the right nasal passage and maxillary recess at the level of the right maxillary 4th premolar tooth (108), extending caudally and invading the ventral aspect of the retrobulbar region, with lysis of the medial wall of the right orbit and rostral aspect of the zygomatic bone at this level. Protrusion of the mass was also noted into the oral cavity, secondary to described lysis of the ventral aspect of the maxillary bone at the level of the right maxillary 4th premolar tooth (108) and right maxillary 1st molar tooth (109) (Figure 1). The right mandibular lymph nodes were mildly enlarged and confirmed to be reactive on cytology. No evidence of lung metastasis was noticed. An intraoral incisional biopsy of the mass was done, and histopathology results were consistent with a mixed odontogenic tumor.

FIGURE 1.

Transverse (A), sagittal (B), and dorsal (C) postcontrast computed tomographic images of the dog’s head, displayed in the soft-tissue window, showing an extensive, multicystic, lobulated, partially mineralized mass centered on the right maxilla (arrows in A to C).

For surgery, the dog was premedicated with dexmedetomidine, induced with propofol, and maintained with inhalant isoflurane in oxygen. Intraoperative analgesia was provided with a constant-rate infusion of fentanyl, ketamine, and lidocaine. Ampicillin and sulbactam were administered IV at induction and every 90 min intraoperatively.

The dog was placed in left lateral recumbency and routine aseptic preparation of the right side of the head and neck was completed. The surgery began with a small cervical approach to the right common carotid artery to place a Rumel tourniquet for temporary ligation, as described by Goodman and Goodman (13). A combined dorsolateral and intraoral approach was then used, as described by Lascelles et al (5). A 1-centimeter margin around the lesion was taken and the mass was resected with the use of a sagittal saw. The cranial 2/3 of the zygomatic arch was resected. Following mass resection, the Rumel tourniquet was removed and no hemorrhage was noticed.

Gloves and instruments were changed. A flap of the fascia of the masseter muscle was applied to support the ventral part of the globe. The base of the flap was located just caudal to the ostectomy site. The length of the flap was determined by the length of the zygomatic arch removed and was slightly overestimated. Two parallel incisions directed toward the angle of the mandible were created. The fascia was then transected perpendicularly to connect the 2 parallel incisions at the ventral extent. A strip of fascia was thus created after dissection from the underlying muscle (Figure 2). The flap was ~1.5 cm wide and 5 cm long. The flap was then transposed and sutured to the levator nasolabialis muscle and subcutaneous tissue with 3 simple interrupted sutures (PDS 2-0) (Figure 3). The oral defect was closed in 2 layers with a labial mucosal flap from the adjacent lip, using polydioxanone (PDS 3-0). The subcutaneous tissue was closed in 2 layers (Monocryl 3-0; Ethicon) in a simple continuous pattern, and the skin was closed with simple interrupted sutures (Ethilon 3-0; Ethicon). The subcutaneous tissue at the level of the cervical incision was closed (Monocryl 3-0) in a simple continuous pattern, and the skin was closed with simple interrupted sutures (Ethilon 3-0).

FIGURE 2.

Schematic representation of the masseter fascia transposition flap procedure in a dog.

FIGURE 3.

Intraoperative images after caudal maxillectomy and zygomatectomy (A) and after masseter fascia transposition flap (B). The dog’s muzzle is to the right.

“*” Indicates the masseter muscle, “#” indicates the orbit, “<” indicates the zygomatic arch, yellow arrow indicates orientation of the flap (in A), and yellow lines indicate margins of the flap (in B).

The dog recovered uneventfully from anesthesia and was managed with a fentanyl constant-rate infusion for 24 h. Mild epistaxis was present but spontaneously resolved after 24 h. The dog was discharged 2 d postoperatively and prescribed carprofen (2.3 mg/kg, PO, q12h for 7 d), codeine (1.8 mg/kg, PO, q8h for 5 d), and gabapentin (10 mg/kg, PO, 8h for 7 d).

Histopathology confirmed a completely excised mixed odontogenic tumor.

Two weeks postoperatively, the dog was presented to the referral hospital for reexamination and suture removal. The incisions were well healed, with symmetric globe positioning and no epiphora on examination (Figure 4). At a 1-year follow-up via telephone, the owner reported that the dog was doing “great.” No ocular asymmetry was noted and no local recurrence was observed.

FIGURE 4.

Photograph of the dog at 2 wk postoperatively.

DISCUSSION

This case report describes the successful use of the masseter fascia as a transposition flap rather than a rotation flap for orbital stabilization following partial inferior orbitectomy in a dog.

The masseter fascia flap has several advantages. The first is the location. It is easily available as it is located directly at the level of the ostectomy. This is also a short and straightforward procedure requiring no specialized equipment. There is the possibility of irradiating relatively quickly after the surgery, since no bone healing is required. The use of prosthetic implants increases the cost and the risk of morbidities such as infection or chronic inflammation (10). As an autologous grafting technique, the masseter fascia flap potentially decreases these risks. Another advantage of the fascia compared to the muscle flap of the masseter is that it may be less likely to atrophy as it includes only fascia with no muscle. However, in a previous case report in which the muscle flap was used, the flap was minimally atrophied due to careful preservation of the deep and superficial vascular supply (4). Sivagurunathan et al (4) reported new bone formation 8 mo postoperatively because the masseter muscle flap created scaffolding for osteogenesis. This observation was not verified in the dog we report and it would have been interesting to obtain a follow-up CT scan.

One disadvantage is the possibility of neoplastic infiltration of this muscle and the need for partial resection, and thus, unavailability for reconstruction (4). If this flap is used when surgical margins are not clean, there is also a risk of tumor seeding.

The length of the flap is limited by the height of the masseter muscle. Comparatively, the temporalis muscle fascia flap described by Dent et al (9) could be longer. However, the temporal fascia flap requires extensive caudodorsal extension of the initial surgical incision and further dissection. For the flap width, a width equal to the diameter of the zygomatic arch at the site of resection was chosen.

The surgeon must remember when designing a transposition flap that rotation of the flap will decrease its effective length. For example, it has been reported that a flap rotation of 90° reduces the flap length by 15% (14). This must be taken into consideration because the height of the masseter muscle is the flap-length limitation. It is therefore relatively easy to judge whether the flap can be used.

As described by Dent et al (9), the rostral anchorage of the flap can be challenging. Sufficient tissue must be present to allow the flap to be sutured to the levator nasolabialis muscle. A rostral hole drilled on the remaining maxillary bone, as in the study of Logothetou et al (10), would have been a way to increase the anchorage of the flap.

Damage to the nasolacrimal duct can occur during caudal maxillectomy, as reported by Sivagurunatha et al (4). Postoperative lacrimation had not been noted in the current case up to 1 y postoperatively. A sialocele secondary to caudal maxillectomy has been described 10 mo postoperatively in a dog (15). This complication had not been noticed in the current case up to the point of the 1-year follow-up. Parotid duct dilation secondary to stenosis has also been reported 2 to 3 y following surgery (16,17). The owners in this case were informed of these delayed complications related to the parotid duct, despite their rarity.

A combined intraoral and dorsolateral approach is recommended for tumors of the mid to caudal maxilla that either arise or extend dorsolaterally (5). The combined approach is generally used for larger tumors. Excessive surgical hemorrhage is more common with maxillectomies done via a combined approach (83%) than with maxillectomies done via an intraoral approach only (54%) (18). To minimize hemorrhage during the resection of the mass in the present case, a Rumel tourniquet was placed at the level of common carotid artery, as described by Goodman and Goodman (13). Another option would have been ligation of the maxillary artery (19).

In conclusion, this case report describes a modification of the masseter fascia flap as a transposition flap to stabilize the globe after caudal maxillectomy and partial orbitectomy in a dog. The cosmetic results related to orbital symmetry and functional outcome were excellent. CVJ