Lateral canthal fibroma in a dog

Abstract

A 9-year-old castrated male pitbull dog was presented for evaluation of a subconjunctival swelling of 10 days duration. On ophthalmic examination, a subcutaneous mass was identified at the right lateral canthus. An excisional biopsy was performed, and histopathological analysis confirmed a diagnosis of a subcutaneous fibroma. Eleven months after surgical excision, the dog had no evidence of recurrence. Fibroma should be included in the differential diagnosis of rapidly enlarging eyelid masses.

Eyelid tumors in dogs are most commonly benign and minimally invasive (1–3). Epithelial tumors are 5 times more prevalent than mesenchymal tumors (1), with sebaceous adenomas being the most frequently reported (1,3). Squamous cell carcinoma, however, is the most common type of eyelid neoplasms in horses, cattle, and cats (4). Mesenchymal tumors arising from the eyelid subcutaneous tissues are fibromas, fibrosarcomas, mastocytomas, and lipomas (1).

Fibromas are rare, locally invasive, and gradually enlarging subcutaneous masses (1). They are benign tumors of fibrocytes with few fibroblasts and abundant collagenous stroma with a pattern of interwoven fascicles and collagen (5). They are rarely reported in humans and dogs, accounting for 0 to 4% of human ocular adnexal tumors (6) and 2.1% of canine eyelid tumors in a study of 202 cases (3).

To the authors’ knowledge, this is the first report of a lateral canthal fibroma in a dog.

Case description

A 9-year-old, castrated male, pitbull mixed-breed dog was presented at the Ophtalmo Vétérinaire Inc. veterinary clinic for evaluation of a subconjunctival swelling at the lateral canthus of the right eye. The lesion was rapidly growing and was noticed by the owner 10 d before presentation. No response to treatment was observed with twice daily application of tobramycin ointment (Tobrex, tobramycine 0.3% ointment; Alcon, Mississauga, Ontario) prescribed by the referring veterinarian.

An ocular examination completed by a Board-certified veterinary ophthalmologist included intraocular pressure evaluation with rebound tonometry (TonoVet tonometer; Tiolet, Helsinki, Finland) followed by slit-lamp biomicroscopy (Kowa, Tokyo, Japan) and indirect ophthalmoscopy (Heine Omega 500 LED Binocular Indirect Ophthalmoscope; Heine Optotechnik, Gilching, Germany) using a 20D double aspheric condensing lens (Volk 20D; Volk Optical, Mentor, Ohio, USA). A soft, 20 × 15 × 15 mm subdermal mass was located at the lateral canthus of the right eye, exposing the mildly hyperemic lateral palpebral conjunctiva (Figure 1). On the skin of the upper left eyelid, a small dark brown oval pedunculated mass of 12 × 6 × 6 mm was noted, 10 mm from the palpebral margin. Both eyes were normotensive with an intraocular pressure of 14 mmHg and 17 mmHg in the right and left eyes, respectively. Findings from the ocular examination were consistent with normal aging (i.e., nuclear sclerosis).

Figure 1.

Clinical appearance of a prominent lateral canthal fibroma in the right eye of a 9-year-old pitbull dog (arrows).

Because of its location, the subdermal mass was hypothesized to be subconjunctival, and was suspected to be a lacrimal cyst. Differential diagnosis included neoplasia, inflammatory granuloma, or abscess. After application of 1 drop of topical anesthetic solution (Alcaine, 0.5% proparacaine hydrochloride ophthalmic solution; Alcon, Mississauga, Ontario), the mass was aspirated using a 25G needle but did not yield fluid. Complete hematology and biochemistry performed by the referring veterinarian 3 d before presentation had revealed no abnormalities. Surgical excision of the mass was recommended and elected by the owner. Dexamethasone, polymyxin, and neomycin drops (Maxitrol, dexamethasone 0.1%, neomycin, polymyxin B solution; Alcon) were prescribed and administered to the right eye, q8h until the procedure, which was scheduled for 6 d later.

An excisional biopsy was conducted under general anesthesia with a 2.5× binocular loupe headset (Heine HR 2.5× High Resolution binocular loupes on a Professional L Headband; Heine Optotechnik). A 25-mm incision was made on the skin overlying the mass using a #15 scalpel blade, 5 mm from the lateral canthus of the right eye. Blunt dissection using Stevens tenotomy scissors isolated a mass that was firm and light pink in color. The mass was excised en bloc and placed in 10% neutral buffered formalin (Simport, Beloeil, Québec) and submitted for histopathologic evaluation (Biovet, Antech Diagnostics). The skin was sutured using 3-0 silk in a simple continuous pattern.

On the same occasion, the pedunculated mass localized on the skin of the upper eyelid of the left eye was cut at the base using Stevens tenotomy scissors. The mass was also placed in 10% neutral buffered formalin (Simport) and submitted for histopathologic evaluation (Biovet, Antech Diagnostics). The wound was closed with a single cruciate suture using 3-0 silk.

Postoperative treatment consisted of dexamethasone, neomycin and polymyxin B drops (Maxitrol, dexamethasone 0.1%, neomycin, and polymyxin solution; Alcon) in the right eye, q12h for 10 d, oral gabapentin (Teva, Toronto, Ontario), 10 mg/ kg body weight (BW), PO, q8 to 12 h for 3 d, oral meloxicam (Rheumocam; Merck & Co, Kirkland, Quebec), 0.1 mg/ kg BW, PO, q24h for 5 d, and oral cephalexin (Apo-cephalex; Apotek, Toronto, Ontario), 20 mg/kg BW, PO, q12h for 7 d. An Elizabethan collar was recommended for the entire duration of treatment and re-examination was recommended for 14 d later.

At re-examination 15 d after surgery, the wounds had healed and minimal residual swelling and mild erythema associated with suture placement were present on the larger wound. At follow-up with the owner by telephone 11 mo after surgery, the dog had no evidence of recurrence.

Both masses were submitted for histopathologic examination. Histologically, the cutaneous mass from the left eye was well-delineated and located in the superficial dermis. The mass was densely cellular and composed of sheets and bundles of interwoven cells supported by a thin fibrovascular stroma. Cells were oval to spindle-shaped with moderately abundant and variably pigmented cytoplasm. Their single nuclei were oval with finely granular chromatin and a single small nucleolus was present. Anisocytosis and anisokaryosis were mild and mitoses were rare. The epidermis had a slight acanthosis and complete margins were included. The mass was diagnosed as a cutaneous melanocytoma with complete excision.

The subcutaneous mass in the right eye was not covered by a dermal surface but was well-delineated and non-encapsulated. The mass was composed of abundant interwoven bundles of collagen with few fibroblasts (Figure 2). Several nests of adipocytes were present. No mitosis was observed, and complete margins were included. The mass was diagnosed as a subcutaneous fibroma with complete excision.

Figure 2.

Photomicrograph of the fibroma (hematoxylin & eosin stain, 200×). Note the few fibroblasts and the abundant interwoven bundles of collagen.

Eyelid tumors are frequently reported in dogs, especially in older animals (2,3,7). Sebaceous tumors, melanomas and papillomas are the most common (2,3,8). According to a study of 119 cases by Wang et al (9), the upper lateral eyelid was more frequently affected.

Fibromas are rarely reported in domestic animals. In both cats and dogs, they are mostly diagnosed in older animals. They appear to be most frequently encountered on the limbs and groin. Boston terriers, Doberman pinschers, boxers, golden retrievers, and fox terriers may be predisposed. The etiology of fibroma formation in animals, as in humans, is unknown, but tumors arise from cutaneous and subcutaneous fibroblasts. These tumors have various shapes and consistencies, and most have a diameter of 1 to 5 cm (10).

Eyelid fibromas are rare, especially in the lateral and medial canthal areas, based on the paucity of reports in the veterinary literature. An ossifying fibroma was diagnosed at the medial canthus of a llama. In this case, the tumor had originated from a tooth (11). A case of canthal fibroma has been reported in humans, although it involved the medial canthus. Contrary to the case described here, this medial canthal mass had been slowly growing over 10 y. Surgical excision was curative (6).

Fibromas, fibropapillomas, and fibrosarcomas are reported in green sea turtles. They are mostly cutaneous but may also occur on the conjunctiva or eyelids. Their etiology is unknown, but the cutaneous forms may be linked to herpesvirus or damage caused by the eggs of a spirorchid trematode. These tumors have typical herpesvirus eosinophilic, intranuclear inclusions. Herpesvirus cutaneous fibroma have also been reported in African elephants and European green lizards (12). Similar inclusions were not observed in the subcutaneous fibroma described in this case report, making a viral etiology unlikely. In horses, cutaneous tumors with a fibroblastic origin known as sarcoids are commonly reported and often involve the eyelids. These tumors most likely have a viral etiology (13). An orbital fibroma has also been reported in the horse (14).

To the authors’ knowledge, this is the first report of a lateral canthal fibroma in a dog. In this case report, the mass was not bothering the dog, but was rapidly enlarging, only noticed by the owner 10 d before presentation. Therefore, a malignant tumor was suspected, and surgical resection was recommended and elected. Various surgical techniques are described to address eyelid neoplasms, ranging from simple excision to various blepharoplasty techniques and adjunctive therapies (15). In this case, the mass appeared to be well-circumscribed and did not involve the eyelid margin. Therefore, a simple excision was performed. Incomplete excision, recurrence, wound dehiscence, or infection are potential complications. In this case, there were no complications associated with the surgical procedure and the excision was curative.

Surprisingly, histopathologic examination revealed a benign process, and complete margins were included. The mass was well-circumscribed, not encapsulated and quite large, which are features of a subcutaneous fibroma. The mass also presented the typical arrangement of interwoven bundles of collagen with few spindle-shaped fibroblasts typical of fibromas (10). No inflammatory cells or mitoses were observed. In contrast to the orbital fibroma reported in a horse, no osseous metaplasia was present (14). The origin of the case presented here is unknown, but could be related to the age of the dog or a previous trauma.

Prior to surgery, since a malignant mass was suspected, thoracic radiographs and a fine-needle aspiration of the draining lymph nodes could have been performed to detect potential metastases. Also, a fine-needle aspiration of the mass could have been helpful in determining the nature of the mass. However, due to financial constraints of the owner and to the short interval between the onset and removal of the mass, the owner elected immediate surgery. Ultrasonography or computed tomography of the head would have been helpful at localizing the origin of the mass.

The dog in this case report had no evidence of recurrence 11 mo after surgery. Fibroma should be included in the differential diagnosis of a rapidly enlarging eyelid mass. Surgical excision appeared to be curative.