The Use of Carbon Dioxide Laser for the Ablation of Meibomian Gland Adenomas in Dogs
Twelve eyelid meibomian gland adenomas in dogs were surgically ablated using the carbon dioxide (CO2) laser. The laser site was not sutured. All procedures resulted in complete removal of the adenoma with no recurrences at 6 months. In addition, no dogs developed corneal disease secondary to the procedure, and the cosmetic appearance of the eyelid margins was good at the end of the 6-month study. Based on results of this study, CO2 laser ablation of canine meibomian gland adenomas is an effective alternative to standard surgical removal.
Introduction
Meibomian gland adenomas are the most frequent eyelid tumors encountered in older dogs and may result in altered eyelid function, discomfort, irritation, ocular discharge, and poor cosmetic appearance.1–4 These tumors often appear as an exophytic protuberance from the eyelid margin, but they may also develop deeply in the eyelid stroma with minimal eyelid distortion. Meibomian gland adenomas are composed of well-differentiated, sebaceous glandular tissue.3,5 Secondary inflammation associated with the tumors can contribute to the size of the mass.4 Most of the tumors have a benign behavior, and local invasion or spread is not documented.2 Early treatment is recommended to preserve normal eyelid function and prevent corneal irritation, especially when the tumor is exophytic with a rough surface. Early intervention also precludes the need for extensive reconstruction procedures and provides for a more functional and cosmetic lid margin.2,6 Surgical removal of these adenomas is commonly performed, and many surgical techniques have been reported. These techniques include full-thickness wedge resection; sliding skin graft (“H”-plasty); cryoablation; bridge flap blepharoplasty (bucket-handle); and cross-lid, semicircular, and rhomboid advancement flaps.2,7–14
A surgical technique using the carbon dioxide (CO2) laser for tumor ablation has also been reported.15 The coherent invisible light beam produced by this laser has a wavelength of 10,600 nm that is absorbed by water molecules in tissues. When the laser energy is transferred to the water molecules, tissue vaporization occurs, providing a means for the ablation of neoplasms.16 Any tissue containing water is affected by this laser energy, so the effects are not proportional to the amount of melanin within the target cells, as is the case with diode lasers. This important characteristic renders the CO2 laser a useful medical laser. Prior reports in animals have described its use for extraocular and adnexal procedures, such as the correction of entropion, removal of distichia, and the resection of bulbar and adnexal masses.17–19 Photokeratotomy using the CO2 laser has also been reported for the treatment of indolent ulcers in dogs, but a recent report concluded that corneal thickness and endothelial cell morphology were altered by the laser energy.17,20 The purpose of this study was to prospectively evaluate the efficacy of CO2 laser ablation of meibomian gland adenomas in dogs.
Materials and Methods
Dogs were presented to the Purdue University Veterinary Teaching Hospital for CO2 laser ablation of eyelid tumors. The dogs with tumors ≥3 mm in width were considered for inclusion in this study. Physical and ophthalmic examinations were performed on each dog, and complete blood counts and serum biochemical profiles were evaluated prior to surgery. Dogs that had no contraindications for general anesthesia underwent biopsy and CO2 laser ablation of their eyelid tumors. Prior to induction of anesthesia, a mixture of acepromazinea (0.02 mg/kg), hydromorphoneb (0.08 mg/kg), and atropinec (0.02 mg/kg) was administered intra-muscularly. Induction and maintenance of anesthesia were achieved with either a mixture of ketamined (5 mg/kg) and diazepame (0.25 mg/kg), or propofolf (6 mg/kg) intravenously. Local anesthesia was achieved by injecting the eyelid tissue with a mixture of nine parts lidocaine hydrochlorideg (2%) and one part sodium bicarbonateh (8.4%). Alkalinization of lidocaine shortens the shelf life of lidocaine, and for this reason the mixture should be prepared just prior to injection.21 Proparacaine hydrochloridei (0.5%) was also applied topically to anesthetize the conjunctiva. No medications were prescribed for postoperative analgesia.
A small amount of tissue was removed with a no. 15 blade for histopathological examination. The remaining tumor tissue was ablated using the laser. Three animals were excluded from the study, because their biopsy results indicated histopathological diagnoses other than meibomian gland adenoma. These masses, however, were also ablated with the CO2 laser at the time of the biopsy, and they included two benign melanomas and a squamous papilloma. A fourth dog, diagnosed with a meibomian gland adenoma, failed to return for any of the recheck examinations and was also dropped from the study. This prospective clinical study was approved by the Purdue Animal Care and Use Committee.
Laser Procedure
Each procedure followed the Purdue University Laser Safety Committee’s protocol.j The tumors were prepared for aseptic surgery with diluted Betadine (5%), and the hair was clipped from the eyelid as needed. The affected eye and periocular region were moistened with saline and covered with wet gauze sponges to protect the adjacent tissue from the effects of the laser. A 0.8-mm, ceramic tip was used to ablate the tumors, and the CO2 laser unitk was set at continuous super-pulse mode and 7 watts of power, which provided a power density of 1393 watts/cm2 and was chosen to obtain sufficient energy delivery for vaporization of the tissue with minimal scar formation at the laser site.22 This power density was in the lower range for producing an incisional and vaporization tissue effect.22 After laser ablation of the surface of the mass, a moistened cotton-tipped applicator was used to remove the inspissated sebaceous material from the neoplastic gland and to cleanse the site. Manual removal of glandular material allowed for less laser energy use. Laser energy was used to ablate all grossly abnormal tissue and was continued until clean margins were observed following cleaning with cotton-tipped applicators. Total ablation was achieved for all 12 tumors. Contracture of the laser site was achieved by defocusing the laser beam to decrease the power density. A similar tissue effect caused by decreased power density may be achieved by decreasing the wattage on the laser unit.
Postoperative Follow-up
All dogs were evaluated immediately after laser ablation and at 7 days, 21 days, and 6 months postsurgery. These reevaluation times provided adequate time for healing and follow-up. Slit-lamp biomicroscopy was used to evaluate the eyelids and cornea at each reevaluation. Fluorescein staining of the cornea was performed at days 7 and 21 postoperatively. Photographs and measurements of the laser site were taken before and after ablation. The width and the thickness of the laser defect were measured and documented in the record. Owners were instructed to apply a combination antibiotic ointment (neomycin, polymyxin B, and bacitracin ophthalmic ointmentl) q 8 hours to the surgical site for 1 week. An Elizabethan collar was not used to prevent self-trauma for any of the dogs after surgery.
Assessment of clinical parameters at the follow-up evaluations included the size of the laser defect, size of the eyelid margin defect, discomfort, conjunctival hyperemia, eyelid hyperemia, cosmetic appearance, and mass recurrence. A grading system was established for these parameters and included scores of none (0), mild (1), moderate (2), and severe (3). Cosmetic appearance was scored as excellent (0), very good (1), good (2), and poor (3). Recurrence of the mass was also noted. An ophthalmic caliperm was used to measure the width of the mass or the width of the laser-induced defect (parallel to the eyelid margin) following ablation, and the thickness of the mass or the lasered site (perpendicular to the eyelid margin) after ablation. This prospective clinical study was not a blinded study, and no control groups were used.
Results
A total of 12 dogs (12 masses) were included in this study following biopsy confirmation of a meibomian gland adenoma. Labrador retrievers (n=3), mixed-breed dogs (n=3), a rottweiler, greyhound, dachshund, Pembroke Welsh corgi, Shetland sheepdog, and golden retriever were included in this study. The dogs ranged in age from 8.0 to 12.0 years (average 9.4 years). Seven castrated males, four spayed females, and one intact female were included in the study. Ten of the masses were located on the lower eyelid, and two were on the upper eyelid. Duration of the eyelid masses ranged from 1 month to 4 years (average 11.3 months). The mean size of the 12 masses was 5.5 × 5.5 mm, with the largest mass being 9.2 × 6 mm (width × thickness) [Figures 1A–1D]. Eight masses involved the entire thickness of the eyelid, and the mean width of these masses was 5.8 mm. Figures 2A–2D and 3A–3D from case nos. 7 and 12, respectively, show an example of a full-thickness eyelid tumor in the former figure and a partial-thickness eyelid mass in the latter. Postoperative results can also be seen in both figures.
Immediately following ablation, the surgical site was typically dry, although there was a small amount of hemorrhage in two cases. The eyelid swelling was associated with the injection of local anesthetic, and it did not increase after the surgical procedure. The laser defect was measured in 12 dogs, and the mean size was 4 × 4 mm (width by thickness) [Table 1]. Contracture of the tissue was responsible for the decrease in lesion size between the initial tumor size and the postoperative defect. The mean width of the postoperative defect recorded from the eight dogs with full-thickness eyelid involvement was 4.8 mm. Figures 4A, 4B illustrate the appearance of case no. 9, which had a full-thickness laser defect. Other clinical parameters were not recorded until day 7 postoperatively.
Day 7 Following Laser Ablation
All 12 dogs were evaluated 1 week following laser treatment, but measurements were only recorded in 11 dogs. One dog was uncooperative, and an exact measurement could not be obtained. The width of the eyelid margin defect ranged from 1.5 to 4.0 mm (mean 2.7±0.7 mm). The mean scores for discomfort, conjunctival hyperemia, eyelid hyperemia, and cosmetic appearance were 0.2, 1.5, 1, and 2, respectively [Table 2]. Only one dog (case no. 8) had signs of discomfort, which started on the fifth postoperative day after he rubbed his head in the snow. The conjunctiva of this dog was moderately hyperemic, and a small, red, raised mass was noted next to the laser site. A small biopsy was taken of the red lesion, and the diagnosis was inflammation, without evidence of neoplasia. This dog remained on topical triple antibiotic ointment and was sent home with an Elizabethan collar. Upon reevaluation 14 days later, discomfort and eyelid hyperemia were much improved, and the eyelid defect had decreased from 3 mm (7 days after laser procedure) to 2 mm.
Day 21 Following Laser Ablation
Ten dogs were evaluated 21 days after the laser procedure. One dog was lost to follow-up, and one returned >21 days and was not included in the 21-day data. Four dogs still had a gap or defect in the eyelid margin at the laser site, with a width of 0.5 to 2.0 mm (mean 1.2±0.7 mm) [Table 1]. The remaining six dogs had granulation tissue at the site and defects that ranged in width from 1.0 to 3.0 mm (mean 1.9±0.5 mm). The eyelid margin was irregular in these latter dogs. The scores for conjunctival hyperemia ranged from 0 to 2 (mean 0.5); scores for eyelid hyperemia were 0 to 2 (mean 0.5); and cosmetic appearance scores were 1 to 2 (mean 1.36) [Table 2]. None of the dogs showed signs of discomfort and/or corneal irritation. One dog had a small, firm, pink, and raised mass of 1.5 × 1.0 mm in the previously lasered area. Recurrence was suspected, but a biopsy revealed focal epithelial hyperplasia and acanthosis without recurrence of the tumor. A second CO2 laser ablation procedure was performed, and reevaluation 1 week later revealed no discomfort (score=0) and only mild conjunctival and eyelid hyperemia (score 1 for each). This dog died of unrelated causes 1 week after the second procedure and was lost to follow-up.
Six Months Following Laser Ablation
Eleven dogs were evaluated 6 months after laser ablation. All dogs had an eyelid scar or eyelid margin irregularity with a mean width of 1±0.5 mm. The scores measuring conjunctival hyperemia were 0 to 1 (mean 0.2); scores for eyelid hyperemia were 0.0; and scores for cosmetic appearance were 1 to 2 (mean 1.36) [Table 2]. No discomfort was noted at the last reevaluation. Most of the laser sites were difficult to visualize with the naked eye, and all owners were pleased with the cosmetic results.
Discussion
The results of the study reported here demonstrated that the CO2 laser was an effective tool for the removal of meibomian gland adenomas, and functional and cosmetic outcomes were achieved. No significant complications were encountered throughout the study, and all owners were pleased with the results. The ease of the procedure, the short hospitalization time, the lack of suture material placement and subsequent removal, and the minimal aftercare associated with this procedure are the major advantages. Perfect eyelid margin apposition and excellent suturing technique are important in other surgical procedures to retain optimal functional and cosmetic results.23 The cosmetic appearance of the wedge resection relies on the quality of wound closure and may vary with surgeon experience. The CO2 laser method is sutureless and, therefore, avoids any secondary problems from sutures, including corneal ulcers. Also, suture removal in some dogs may require heavy sedation or short generalized anesthesia.
For the purpose of this study, the laser procedures were performed under short generalized anesthesia, with adjunctive local anesthesia to decrease the local laser stimulus and also to create similar conditions to this procedure performed without general anesthesia. The authors have also performed this laser technique on cooperative animals using only local anesthesia, and light sedation if needed. Most other surgical techniques to remove eyelid tumors require general anesthesia, with the exception of cryoablation, which can be performed under the same conditions as the CO2 laser procedure. When the procedure is done on a conscious dog, the help of a veterinary assistant is required for adequate restraint. Judicious selection of dogs is required, as there are increased risks of lasering the surrounding tissues by mistake in uncooperative, moving animals. The noise from the vacuum system appears to be the most disturbing factor for the awake dog. Turning on the vacuum prior to laser ablation may habituate the dog to the sound.
To reduce the risk of inadvertent laser damage to the cornea, the normal eyelid may be used as a natural shield to cover the cornea. A small amount of water-based geln may also be applied to the cornea for further protection, as such products absorb some of the laser energy. Petroleum-based ointments should not be applied to the cornea prior to surgery because of the risk of flash fire from igniting the petroleum with the laser energy. Wavelength-specific laser corneal shieldso are also commercially available and can be positioned over the cornea for further protection. Safety concerns accompany all laser procedures, and surgeons must precisely follow predetermined safety protocols to protect both animals and medical staff.24
The average age of dogs in this study was 9.4 years, which agreed with a previous report on eyelid masses.2 In that study by Roberts et al., more upper eyelid masses (83.3%) were treated than lower eyelid masses (16.7%). In addition, they found that the upper eyelid was involved in 52.7% of affected dogs.2 Another report by Krehbiel and Landham on 202 canine eyelid neoplasms indicated that 39.7% of the sebaceous adenomas involved the upper eyelid, 29.3% involved the lower eyelid, 5.1% were found at one of the canthi, and the location was unspecified in 25.9%.25
Other surgical techniques for the removal of eyelid masses, such as the full-thickness wedge resections, bridge-flap blepharoplasty, “H” plasty, semicircular flap, cross lid flap, rhomboid flap, and cryotherapy have been reported.7,9–12,26–29 The main factors governing technique selection are the size of the mass to be removed, its location, and whether malignancy is suspected. Wedge resections are the most popular procedure, owing to their simplicity and no need for specialized instruments. In a retrospective study of 200 cases of palpebral neoplasms in dogs, 31.8% underwent full-thickness wedge resection (three- or four-sided), 60.1% had cryosurgery, and the remaining animals were treated with more extensive surgeries, radiofrequency, or immunotherapy.2 The cosmetic appearance outcome in that report was considered to be most acceptable following cryosurgery; however, the assessment of postsurgical cosmetic appearance was difficult to assess retrospectively.2 All the dogs in the present study had a small scar at the tumor site when evaluated with magnification. Seven of the cases had no visible scar (as evaluated without magnification) and minimal eyelid irregularity at 6 months. Some of the scars needed manipulation of the eyelid to be seen, as they were located on the conjunctival side of the eyelid.
Cryosurgery using nitrous oxide or liquid nitrogen appears to cause more discomfort, swelling, epiphora, tissue sloughing, adnexal damage, and subsequent depigmentation than does CO2 laser ablation.12,30 The swelling and chemosis that occurs following CO2 laser ablation was caused by the local injection of lidocaine and was present before applying laser energy to the eyelid. These clinical changes resolved within 12 to 48 hours as the drug was reabsorbed. Local injection of lidocaine in the palpebrae can be a difficult procedure on an awake patient. The pain associated with the injection can be minimized with alkalinization of the lidocaine by sodium bicarbonate.21,31,32
Two of the 12 dogs in this study had very small, raised masses at the surgical site during either the 7- or 21-day recheck, but neither mass was a recurrence of the tumor. Self-induced trauma was most likely the cause of inflammation seen in the first dog (case no. 8), and focal epithelial hyperplasia and acanthosis from unknown causes were found in the second dog (case no. 6). The changes seen in the second dog frequently arise secondary to an inflammatory process, and they may have occurred from the postoperative surgical inflammation associated with the procedure.
Conclusion
In this study, the CO2 laser was an effective technique for the removal of meibomian gland adenomas in dogs. Results demonstrated good cosmetic appearances, even without suturing to close the laser site. No functional alteration of eyelids and no secondary corneal diseases were noted throughout the study. The side effects such as discomfort, conjunctival hyperemia, and eyelid hyperemia were minimal, and the final cosmetic appearances were good to very good. All owners were pleased with the procedure and the final outcomes of this clinical study. The ease of the procedure, the short hospitalization time, and the minimal discomfort and aftercare (including not using an Elizabethan collar following the procedure) were also significant advantages. Because of the possible concern associated with the removal of eyelid margin, further study is necessary to assess the maximal amount of lid margin that can be removed with this technique.
Acepromazine Maleate Injection; Phoenix Pharmaceutical, St. Joseph, MO 64503
Hydromorphone Hydrochloride; Baxter, Deerfield, IL 30015
Atropine Sulfate Injection; Phoenix Pharmaceutical, St. Joseph, MO 64503
VetaKet; Lloyd, Shenadoah, IA 51601
Diazepam; Abbott Laboratories, North Chicago, IL 60064
PropoFlo; Abbott Laboratories, North Chicago, IL 60064
Lidocaine Hydrochloride Injectable; Phoenix Pharmaceutical, St. Joseph, MO 64503
Sodium Bicarbonate 8.4%; American Regent Laboratories, Shirley, NY 11967
Proparacaine Hydrochloride Ophthalmic Solution USP 0.5%; Bausch & Lomb, Tampa, FL 33637
Purdue University Safety Laser Protocol
Accu Vet Novapulse; Luminis, Santa Clara, CA 95054
Neomycin and Polymyxin B Sulfate and Bacitracin Zinc Ophthalmic Ointment USP; Fougera, Melville, NY 11747
Jameson Caliper; Storz, St. Louis, MO 63122
K-Y Lubrication Jelly; Johnson & Johnson, Arlington, TX 76004
COX II; Oculo-Plastic, Montreal, Quebec, H3L 1Y9 Canada
Citation: Journal of the American Animal Hospital Association 41, 4; 10.5326/0410227
Citation: Journal of the American Animal Hospital Association 41, 4; 10.5326/0410227
Citation: Journal of the American Animal Hospital Association 41, 4; 10.5326/0410227
Citation: Journal of the American Animal Hospital Association 41, 4; 10.5326/0410227
Meibomian gland adenoma on the lower eyelid of a 12-year-old dachshund (case no. 1). Preoperative photos (A, B); laser defect following CO2 laser ablation (C); and 6 months after laser ablation (D).
Meibomian gland adenoma on the lower eyelid of an 8-year-old Shetland sheepdog (case no. 7).Preoperative photo (A); laser defect following CO2 laser ablation (B); and 6 months after laser ablation (C, D).
Meibomian gland adenoma on the upper eyelid of an 8-year-old rottweiler (case no. 12). The mass is extending deep into the palpebral conjunctiva (A). Laser defect following ablation, with chemosis from the injection of local anesthetic (B). Three weeks (C) and 6 months after laser ablation (D).
Meibomian gland adenoma on the upper eyelid of an 8-year-old Labrador retriever (case no. 9) prior to (A) and immediately after (B) CO2 laser ablation.
