History

A 14-year-old 6.62-kg spayed female Bichon Frise was presented to the veterinary clinic due to a conjunctival mass in the right eye (OD) noted by the owner 1 month earlier. The patient had been otherwise healthy without relevant behavioral and physical changes. A 2.5 X 1.5 X 1.5-cm soft mass was located in the conjunctiva of the lower lateral eyelid in OD (Figure 1). Medical management with Neo-Poly-Dex ophthalmic suspension 5 mL (neomycin, 3.5 mg; polymyxin B sulfate, 10,000 units; and dexamethasone, 0.1%; 1 drop, q 12 h for 14 days) was started. The patient returned 3 months later for a follow-up examination.

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Physical examination of a 14-year-old 6.62-kg spayed female Bichon Frise with a conjunctival mass in the right eye (OD) noted by the owner 1 month earlier. A—A 2.5 X 1.5 X 1.5-cm soft mass was in the conjunctiva of the lower lateral eyelid in OD (black arrowhead). B—The patient returned 3 months later for a follow-up, and the OD conjunctival mass was bigger and measured 4 X 3.5 X 1.5 cm, involving the lower conjunctiva and extending dorsally and ventrally, occluding the eye (black arrowhead). C—The OD was visible postoperatively, and after topical application of Proparacaine HCl 0.15%, a centrally located 0.1-cm-diameter nonulcerative keratitis was noted (white arrowhead), slightly dorsolateral to a 0.2 X 0.3-cm corneal opacity and surrounded by diffuse corneal edema and neovascularization. D—At the follow-up 6 weeks after the surgical removal, there was a swelling of the dorsolateral conjunctiva of OD (white arrowhead), with no overt mass palpated.

Citation: Journal of the American Veterinary Medical Association 262, 12; 10.2460/javma.24.06.0389

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Clinical and Gross Findings

On follow-up physical examination, the OD conjunctival mass was bigger and measured 4 X 3.5 X 1.5 cm, involving the lower conjunctiva and extending both dorsally and ventrally, occluding the eye (Figure 1). The patient underwent surgical intervention to remove the mass after sedation and anesthesia with butorphanol (Torbugesic; 0.5 mg/kg, IV) and dexmedetomidine (Dexdomitor; 0.5 mg/mL solution, IV). After the procedure, the patient recovered with atipamezole (Antisedan; 5 mg/mL solution, IV). A large portion of a tan, friable, lobulated tissue was removed with blunt dissection. The OD was visible postoperatively, and after topical application of proparacaine HCl 0.15%, a centrally located 0.1-cm-diameter nonulcerative keratitis (with fluorescein dye) was noted, slightly dorsolateral to a 0.2 X 0.3-cm corneal opacity and surrounded by diffuse corneal edema and neovascularization. The tissue sample from the mass was collected, fixed in neutral-buffered 10% formalin, and routinely processed for histologic examination. Postoperative medical management included carprofen (2 mg/kg, PO, q 12 h for 14 days), amoxicillin (10 mg/kg, PO, q 12 h for 14 days), doxycycline (5 mg/kg, PO, q 12 h for 14 days), and Neo-Poly-Dex ophthalmic suspension 5 mL (neomycin, 3.5 mg; polymyxin B sulfate, 10,000 units; and dexamethasone, 0.1%; 1 drop, q 12 h for 14 days). At the follow-up 6 weeks after the surgical removal, there was a swelling of the dorsolateral conjunctiva of OD with no overt mass palpated. The next revision was scheduled for in a month.

Histopathologic Findings

Histopathologic specimens were submitted to a commercial laboratory (Antech Diagnostics; Mars Petcare Science & Diagnostics) for evaluation. The tissue submitted consisted of a multinodular mass composed of lobules of round to polygonal cells arranged in sheets separated by collagenous trabeculae (Figure 2). The neoplastic cells had distinct cell borders, round eccentric nuclei, finely stippled chromatin, prominent central nucleoli, and abundant eosinophilic granular cytoplasm. Anisocytosis and anisokaryosis were mild. The mitotic count was 1 in 10 standardized hpf (400X; 2.37 mm²). There were frequent small pools of lightly basophilic mucinous material separating cells. No ducts were present within the lobules. Multifocal hemorrhagic foci and aggregates of hemosiderin-laden macrophages were dispersed throughout the neoplasm.

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Photomicrographs of the lobulated friable conjunctival OD mass removed from the 14-year-old 6.62-kg spayed female Bichon Frise in Figure 1. A—The tissue submitted included a multilobular mass composed of lobules of round to polygonal cells arranged in sheets separated by collagenous trabeculae. H&E stain; bar = 200 μm. B—The neoplastic cells have distinct cell borders, round eccentric nuclei, finely stippled chromatin, prominent central nucleoli, and abundant eosinophilic granular cytoplasm. H&E stain; bar = 60 μm.

Citation: Journal of the American Veterinary Medical Association 262, 12; 10.2460/javma.24.06.0389

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Morphologic Diagnosis and Case Summary

Morphologic diagnosis and case summary: canine lobular orbital adenoma.

Comments

Lobular orbital adenoma is a distinct clinical entity recognized in dogs composed of well-differentiated glandular tissue lacking ducts.¹ The histologic origin of this neoplasm has not been confirmed, although it is speculated that the neoplastic cells arise from lacrimal glands or zygomatic salivary glands.^1–3 Neoplastic cells are arranged in solid aggregates or acini within the lobules and have abundant granular cytoplasm with periodic acid–Schiff–stained granules and small, round nuclei.¹ Anisokaryosis and anisocytosis are mild, and mitotic figures are absent to low.² Publications detailing the immunohistochemical characterization are lacking.² Grossly, this neoplasm appears as friable and multinodular or solid subconjunctival, palpebral, or retrobulbar masses, with other ocular signs including third eyelid protrusion, periocular swelling, exophthalmos, strabismus, and resistance to retropulsion.^1–3 The neoplasm can be unilateral or bilateral and often involve the orbit.¹ Lobular orbital adenomas occur in middle-aged and older dogs and have been reported in numerous breeds.^1,3

Despite the benign histologic features, the prognosis of the lobular orbital adenoma is guarded since recurrence is common.^2,3 In a retrospective study,¹ the recurrence rate after surgical excision was 76.9% (10/13) and recurrence was reported to occur between 90 to 665 days after surgery, with an average time of 395 days. Exenteration was performed in only 3 patients for this study, resulting in a lack of recurrence in 2 cases.¹ Most of the patients in the study were eventually euthanized for causes unrelated to the neoplasm.¹ The histopathology report documented an incomplete excision in the case report herein. Since the tissue was very friable, only the larger fragments of the excised mass were submitted for histologic evaluation. At the follow-up 6 weeks after the surgical removal, there was a swelling of the dorsolateral conjunctiva of OD, with no overt mass palpated. The nonulcerative keratitis and corneal opacity resolved. Thus, the Neo-Poly-Dex topical treatment was discontinued. It was planned that the patient would be periodically monitored for evidence of recurrence, given that the average time to recurrence is over a year.¹ The next revision was scheduled for in a month. However, due to the high recurrence rate of this neoplasm, enucleation and exenteration of the OD may be required to decrease the risk of recurrence.^2,3 Metastases or osseous destruction and invasion have not been described in this neoplasm.¹

To improve preventative measures and treatment of lobular orbital adenomas, possible underlying causes have been analyzed. However, papillomavirus DNA was not retrieved after PCR evaluation of 37 canine orbital adenoma samples (1 fresh tissue sample and 36 formalin-fixed paraffin-embedded tissues).³ Papillomavirus DNA was not identified from conjunctival tissue samples from 10 dogs used as controls.³ Further metagenomic analysis of DNA viruses with targeted sequence capture was performed on 31 formalin-fixed paraffin-embedded tissues from lobular orbital adenomas and 10 fresh samples from canine conjunctiva and identified canine parvovirus in 6.4% of the neoplasms and 20% of the normal conjunctival tissue.⁴ However, despite these findings, an association between lobular orbital adenomas and DNA virus is unlikely and the etiology of this neoplasm remains unknown.⁴

Disclosures

Drs. Labelle and Negrão Watanabe are employed by Antech Diagnostics, Mars Petcare Science & Diagnostics. The author(s) declare that no financial support was received for the research, authorship, and/or publication of this article. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

No AI-assisted technologies were used in the generation of this manuscript.

Funding

The authors have nothing to disclose.

ORCID

D. Barrantes Murillo https://orcid.org/0000-0002-0744-3774