Canine retrobulbar lipoma excision through a ventral transpalpebral anterior orbitotomy

Abstract

A 5-year-old spayed female German shepherd dog was referred for diagnostic evaluation and treatment of progressive exophthalmos, conjunctival hyperemia, and protrusion of the third eyelid of the left eye. Computed tomography revealed a retrobulbar mass of the orbit, exhibiting radio attenuation consistent with adipose tissue and well-defined margins. No evidence of metastasis was detected on thoracic radiographs or abdominal ultrasound. Cytological evaluation of ultrasound-guided fine-needle aspirates was inconclusive. A ventral transpalpebral anterior orbitotomy approach facilitated excision of the abnormal retrobulbar tissue. Histopathology revealed mature adipose cells compatible with a lipoma. The patient regained normal appearance and function 3 months after surgery.

Key clinical message:

While rare, consider a lipoma as a differential diagnosis for a retrobulbar mass. The ventral transpalpebral orbitotomy has been described in only 3 cases in the veterinary literature, and this is the only known report of utilizing this approach for excision of a neoplastic condition.

Due to the confined space of the orbit, a retrobulbar mass can result in various clinical signs. In a retrospective study of 25 small animal cases published in 2001, the most commonly identified signs were exophthalmos (84% of cases), conjunctival hyperemia (40%), protrusion of the nictitating membrane (28%), exposure keratitis (20%), and fundic abnormalities (20%) such as retinal detachment, edema, and vascular changes (1). Etiologies for a retrobulbar mass include inflammatory causes (such as abscessation, cellulitis, trauma, and hematoma formation), immune-mediated conditions, orbital cyst-type lesions (such as sialoceles), vascular anomalies, emphysema, or neoplasia (2–10).

A lipoma is a benign tumor of mesenchymal origin arising from fat and is one of the more commonly diagnosed canine neoplasms. Lipomas could develop anywhere on the body within the subcutis (11) but could also develop in body cavities or deeper planes of fascia and muscle (4,11–13). These tumors can be asymptomatic but they can cause functional deficits when in specific locations, such as the orbit.

This report describes an orbital lipoma and highlights its rarity in anatomic location as well as the surgical approach. Surgical resection of an orbital lipoma in a dog was the focus of 1 previous case report (14). In that case, the lipoma was protruding from the dorsal conjunctival sac and accessible through a transconjunctival orbitotomy. In the present case, the retrobulbar space was accessed through the recently described ventral transpalpebral orbitotomy (15) and this is the first report of the excision of a benign neoplasm using this surgical approach.

Case description

A 5-year-old spayed female German shepherd dog was presented to the Atlantic Veterinary College (AVC) for evaluation of a 1-month progressive history of exophthalmos and protrusion of the third eyelid oculus sinister (OS). A full ophthalmic examination was performed by a Board-certified veterinary ophthalmologist prior to referral. The patient had a 1-year history of pannus and corneal dystrophy oculus uterque (OU); the pannus was managed with topical 1% prednisolone acetate (unknown brand) OU. Otherwise, the patient was considered to be in good systemic health. The patient was an active seeing eye guide dog and was dependent on vision for her work.

The patient was bright, alert, and responsive with all vital parameters within acceptable limits. Exophthalmos, conjunctival hyperemia, and protrusion of the third eyelid were observed OS (Figure 1A), and both eyes were assessed to have positive direct and consensual pupillary light reflexes and a positive bilateral menace response. No pain was evident upon local digital palpation or opening of the jaw, and no ocular or nasal discharge was noted. Retropulsion was decreased OS compared to oculus dexter (OD). A complete blood cell count and serum biochemistry were performed, with results within reference ranges.

Figure 1.

Progression of the patient’s exophthalmos on presentation (A), 12 h (B), 4 wk (C), and 6 mo (D) after surgery.

An ocular ultrasound was performed by a Board-certified veterinary radiologist with the patient under general anesthesia. A well-defined hypoechoic mass with multifocal areas of mixed echogenicity located posterior and slightly inferior to the left globe was identified. After preparation of the dorsal conjunctival fornix with 1:50 povidone-iodine solution, transconjunctival ultrasound-guided fine-needle aspirates were collected for cytological evaluation. Results were inconclusive as they were either primarily acellular or contaminated with a moderate amount of blood.

Computed tomography (CT) imaging (Aquilon TSX-101A; Toshiba Medical Systems Corporation, Tustin, California, USA) with 0.3-mm slices identified a hypoattenuating space-occupying retrobulbar mass of the left eye with similar Hounsfield units (–100 HU) to the surrounding retrobulbar fat OS and that of the right eye (Figure 2). Despite causing rostral, dorsal, and lateral displacement of the left globe, the mass appeared to have well-defined margins and normal-appearing surrounding anatomy, with no contrast enhancement. The mass caused ventral displacement of the ventral rectus muscle and dorsomedial displacement of the medial and dorsal rectus muscles, as well as dorsolateral displacement of the lateral rectus muscle and optic nerve. Further diagnostic imaging consisted of 3-view thoracic radiographs and an abdominal ultrasound, which did not reveal evidence of metastasis.

Figure 2.

Axial (A) and coronal (B) CT images in a soft tissue window, post-contrast administration. Note the well-demarcated fat-like hypo-attenuating lesion in the caudal aspect of the left orbit (asterisks).

Based on CT results, a working diagnosis of a primarily lipid-based tumor was made, with no evidence of local or distant spread of disease. Excisional biopsy of the retrobulbar mass was therefore elected. The patient was premedicated with hydromorphone (Hydromorphone; Sandoz, Boucherville, Quebec), 0.05 mg/kg body weight (BW), IM and dexmedetomidine (Dexdormitor; Zoetis, Kalamazoo, Michigan, USA), 9 μg/kg BW, IM. General anesthesia was induced with alfaxalone (Alfaxan; Abbott Laboratories, Saint Laurent, Quebec), 1 mg/kg BW, IV, and maintained with isoflurane inhalant throughout the procedure. The patient was placed in sternal recumbency, and the surgery site was aseptically prepared with 1:50 povidone-iodine solution. Cefazolin (Fresenius Kabi Canada, Toronto, Ontario) was administered at 22 mg/kg BW, IV, every 90 min of surgery. Two stay sutures of 4-0 PDS (Ethicon; Johnson & Johnson, Bridgewater, New Jersey, USA) were placed on both the temporal and nasal aspects of the lower eyelid allowing the skin below the eyelid margin to remain taught. A 4-cm incision was then made approximately 1.5 cm below the inferior palpebral lid margin above the ventral orbital rim with a #15 surgical blade, providing a ventral transpalpebral anterior orbitotomy approach. Access to the ventral orbit was achieved through a combination of blunt dissection using Metzenbaum scissors, undermining of connective tissue and extending the skin incision 0.5 cm temporally. Two additional stay sutures were placed on both the dorsal and ventral aspects of the incision allowing for visualization of the rostral aspect of the mass, which was located below the ventral margin of the third eyelid. Care was taken to ensure the third eyelid and gland of the third eyelid were left intact; the approach was ventral to both of these structures, yet dorsal to the ventral orbital floor. A Lone Star Ring retractor (Jorgenson Laboratories, Loveland, Colorado, USA) was placed in the incision site to provide even, circumferential retraction of the incision (Figure 3). Care was taken to avoid excessive traction on the mass due to the proximity of the globe and the optic nerve. A 1 cm wide malleable retractor was also used when needed to apply gentle dorsolateral retraction on the globe. Due to the fatty nature of the mass, en bloc removal proved challenging, with the mass fragmenting easily when manipulated; a variety of surgical instruments were used. En bloc removal was successful with the use of a bladder spoon in conjunction with Adson tissue forceps. As the mass easily separated with minimal manipulation after removal, several pieces were submitted for histopathology. After excision of the mass, absorbable gelatin sponge (Surgifoam Ethicon, Somerville, New Jersey, USA) was placed behind the globe to minimize dead space and prevent enophthalmos after surgery, as a significant amount of the orbital fat pad was removed along with the mass. The third eyelid was replaced into anatomical position and sutured with 4-0 Monocryl (Ethicon), due to disruption of the ventral attachments of the third eyelid gland during blunt and sharp dissection. The deep subcutaneous tissue was closed with 4-0 Monocryl in a simple continuous pattern, and the dermis was apposed with 5-0 Monocryl in an intradermal pattern.

Figure 3.

Intra-operative image of the ventral transpalpebral orbitotomy with exposure of the retrobulbar mass (arrow). A Lone Star Ring retractor and stay sutures are utilized to increase visualization.

Multiple sections of the mass were submitted for histopathology, the largest of which measured approximately 3 cm × 1 cm and accounted for approximately half of the total mass. All sections of tissue were histologically similar lobules of mature adipocytes supported by collagenous stroma. The adipocytes were of a uniform population of polygonal cells with distinct cell margins, abundant clear cytoplasm and a single large delineated cytoplasmic vacuole that displaced the small bland ovoid nucleus to the periphery of the cell, extending to the margins of the excised tissue. No mitotic figures were identified. Based on gross and histological findings, the mass consisted of mature adipose tissue, compatible with that of a lipoma.

Following recovery from general anesthesia, marked periorbital and conjunctival swelling, as well as moderate exophthalmos OS were present (Figure 1B). Fluorescein stain was retained OS and negative OD, indicating a superficial, axial corneal ulcer OS. The 1% prednisolone acetate used for the management of pannus OU by the referring veterinary ophthalmologist was temporarily discontinued and tobramycin 0.3% topical ophthalmic solution (Tobramycin; Sandoz Canada) was administered OS q8h for 7 d. Post-surgical analgesia was provided with meloxicam (Metacam; Boehringer Ingelheim, St. Joseph, Missouri, USA), 0.1 mg/kg BW, PO, q24h for 5 d and gabapentin (Apotex, Toronto, Ontario), 11 mg/kg BW, PO, q12h to q8h for 5 d. Fluorescein stain performed 7 days after surgery was negative OU; tobramycin 0.3% ophthalmic was discontinued, and treatment for pannus with prednisolone acetate 0.1% ophthalmic solution OU was resumed.

The 4-week postoperative recheck revealed mild exophthalmos OS (Figure 1C), and the third eyelid was prolapsed, covering approximately 25% of the cornea. The Surgifoam which was placed within the retrobulbar space during surgery, was expected to slowly resorb over 4 to 6 wk, as per the manufacturer’s information. It was anticipated that the globe and third eyelid would return to a normal anatomic position over that period. Twelve weeks after surgery, the owner reported by telephone that the patient’s exophthalmos had resolved and there were no apparent visual deficits. The patient had a normal appearance 6 mo after surgery (Figure 1D).

Discussion

In a large retrospective study of humans, lipomas comprised less than 1% of total orbital lesions evaluated (16), making this condition rare among humans as well as among animals. The case presented here describes the unusual anatomic location for a lipoma, with only 1 other case report in the veterinary literature (14). Benign tumors represent only 10% to 25% of reported retrobulbar neoplasia (1) with other possibilities including meningioma, fibroma, and fibrous histiocytoma.

In this case, the patient had non-painful progression of unilateral exophthalmos over an approximately 4-week period, consistent with the progress of an orbital neoplastic condition (1,2,17). It should be noted that presence or lack of pain should not be a definitive factor in developing a complete differential diagnoses list, as swelling and pain can be present with tumor necrosis (2).

Differential diagnoses for a lipomatous orbital mass include an infiltrative lipoma, liposarcoma, and prolapsed orbital fat (18). Prolapsed orbital fat represents 2% of orbital lesions in humans (16), and has been reported in several veterinary patients (18,19). A significant difference between the orbital fat prolapse and a retrobulbar lipoma is the resulting mass effect. Patients with orbital fat prolapse develop enophthalmos, while those with a retrobulbar lipoma develop exophthalmos. Rare reports of orbital hibernomas, neoplasm of brown fat, have also been published recently and contribute to the list of differentials for a benign orbital mass (20,21).

Ventral transpalpebral anterior orbitotomy was chosen as the surgical approach in this case for several reasons. Firstly, based on the working diagnosis, a wide margin for excision was not indicated, so exenteration and orbitectomy were considered radical. Furthermore, the ventral transpalpebral orbitotomy decreased the likelihood of globe and optic nerve manipulation; osteotomies were avoided, and the approach facilitated adequate exposure to the ventromedial orbit and the retrobulbar space without extensive disruption of orbital tissues. Normal palpebral fissure anatomy was also maintained. This approach was first described in the veterinary literature in 3 canine cases by McDonald et al (15) for a retrobulbar abscess, a mucoceole, and necrotizing sialadenitis. One patient in that case series had blindness as a long-term complication due to an undetermined etiology, and another patient had a superficial corneal ulceration which resolved uneventfully, similar to the present case. McDonald et al (15) hypothesized that blindness as a postoperative complication was localized to a preganglionic lesion with possible etiologies including optic nerve compression, postoperative inflammation associated with the optic nerve, or surgical manipulation. In that case, optic nerve compression seemed most likely based on the significant mass effect of the mucoceole, and did not appear to be attributable to surgery (15).

A ventral transpalpebral anterior orbitotomy facilitates exposure of the ventral orbital floor and is appropriate for lesions in a similar location described in this report, as well as those described in the 2016 McDonald et al (15) case series. Until now, this surgical approach has not been reported in the treatment of a neoplastic condition. This approach may not be appropriate for disease processes that are more extensive or infiltrative, or which require adequate access to the lateral or dorsal orbital regions. None of the reported cases to date, including the present case, utilizing this surgical approach has had a recurrence of orbital disease within their follow-up time frames (2 y for the retrobulbar abscess and mucoceole cases, and 2 mo for the necrotizing sialadenitis case) (15).

In the only other reported orbital lipoma in the veterinary literature, a trans-conjunctival approach was performed (14) which may have resulted in less orbital exposure than the transpalpebral approach described here. Avoiding the third eyelid and the associated lacrimal gland may be possible in both approaches; however, less manipulation of the third eyelid was expected with the transpalpebral approach. Additionally, leaving the lid margin architecture intact is of significant benefit, as alterations to the lid margins can interfere with tear film distribution and therefore corneal health (22). As this patient already had a progressive corneal disease (pannus), decreasing the likelihood of additional corneal irritation was a priority. With the transpalpebral approach there was no need for conjunctival suture, which was used in the transconjunctival approach. Conjunctival suture can result in additional corneal irritation depending upon its placement. Minimal hemorrhage was encountered in the case using the transconjunctival orbitotomy (14) and this may be a benefit as compared to the transpalpebral approach.

McDonald et al (15) reported that exophthalmos and soft tissue orbital swelling resolved within 2 wk of surgery in all 3 cases. In the case presented here, exophthalmos did not resolve until 4 wk after surgery. Considerations for the longer duration of postoperative exophthalmos and soft tissue orbital swelling include the use of Surgifoam (Ethicon) in the retrobulbar space and a difference in postoperative anti-inflammatory medication. McDonald et al (15) administered oral prednisone after surgery (with initial doses ranging from 1.0 to 2.2 mg/kg BW per day) for anti-inflammatory purposes; whereas in our case, a non-steroidal anti-inflammatory drug (NSAID) was used to manage postoperative inflammation. Non-steroidal anti-inflammatory drugs are known to be less potent than corticosteroids with regard to their anti-inflammatory properties (23). Our decision to manage postoperative pain and inflammation with an NSAID was to avoid potential decreased wound healing time and to avoid side effects commonly associated with steroid administration. Meloxicam was a good option in this case as it has been shown efficacious for postoperative soft tissue analgesia and inflammation (24–27).

While the primary indication for Surgifoam, a porcine gelatin absorbable sponge frequently used in both human and veterinary surgery, is for hemostatic purposes, intra-operative hemorrhage in this case was controlled with electro-cautery and direct pressure. The Surgifoam that was inserted into the retrobulbar space was used to prevent postoperative enophthalmos, which likely contributed to moderate exophthalmos OS for several weeks after surgery; this exophthalmos was no more severe than what was present before surgery. The sponges are expected to be compressed and resorbed over 4 to 6 wk. In our case, it was expected that a near-normal appearance to the patient’s orbit and globe would be achieved within that time frame. Porcine-derived hemostatic sponges have been determined to be safe for use in veterinary patients as persistent postoperative complications and hypersensitivity reactions, while reported in humans, do not appear to occur with any significant frequency in veterinary patients (28).

In the case herein, transient expansion of the Surgifoam was expected to potentially result in exophthalmos rather than impacting the retrobulbar tissues such as the optic nerve. This may be due to the anatomy of the canine orbit and the incomplete bony enclosure, allowing some degree of outward soft tissue expansion. However, this should still be recognized as a potential risk for using a hemostatic sponge in the retrobulbar area. Some degree of retraction of the orbital soft tissues was also expected in the later postoperative period due to fibrosis, which increased the concern for postoperative enophthalmos and supported our decision to leave the Surgifoam in the retrobulbar space at the time of surgery. This was in contrast to the report by Alander et al (29) to not leave Surgifoam in a confined space.

This case is the second report of an orbital lipoma in the veterinary literature, and the first report of a ventral transpalpebral orbitotomy for surgical treatment of a neoplastic process. This surgical approach should be considered in cases of focal, non-invasive retrobulbar disease and for acquiring incisional or narrow margin excisional biopsy which increases the likelihood of a definitive diagnosis. Fortunately, exenteration of the orbit and removal of a visual eye was avoided in this case owing to a thorough pre-operative diagnostic evaluation and application of this surgical approach. CVJ