Ординатура / Офтальмология / Английские материалы / Small Animal Ophthalmology Secrets_Riis_2002

Figure 2. A melanoma on the upper lid. These are locally invasive but usually do not metastasize.

Figure 3. A squamous cell carcinoma of the lower lid. These can be a challenge (see Chapter 27).

conjunctiva. Other tumor types that have been reported include meibomian gland adenoma and adenocarcinoma, basal cell tumor, melanoma, mast cell tumor, and fibroma/fibrosarcoma (Figs. 4 and 5).

5. Are all mass lesions neoplastic?

Some conditions of the eyelid may be difficult to distinguish from neoplasms (e.g., granuloma, chalazion. and even some acute lesions such as marginal inflammatory conditions). Patient history can be helpful in the identification because most lid tumors tend to grow gradually rather than rapidly. A lesion that is bilateral and symmetric is unlikely to be neoplastic. Eyelid lesions that are associated with pruritus are less likely to be neoplastic (mast cell tumor may be the exception). If all lids are affected with nodules, consider immune-mediated blepharitis or sterile pyogranulomas as a possible etiology. The diagnosis is best made with histopathology of an area of affected lid margin.

6. How can I tell if a tumor is benign or malignant?

Histopathology is recommended for all lid tumors. Without it, you cannot be 100% sure whether you are dealing with a benign or malignant process. However, several characteristics point to malignant neoplasms and may prove useful tools during examination of the eyelids.

7.If the mass is not irritating to the cornea, why remove it?

As discussed earlier, although many lid tumors will be benign, it is not always possible to

differentiate their behavior based on examination only, and many benign lid tumors will still cause extensive local destruction of tissue if left untreated. For many patients requiring extensive reconstruction, early intervention may have prevented procedures that prove to be more uncomfortable for the patient and more costly to the client. Therefore, it is becoming widely accepted

Figure 4. Multiple conjunctival tumors which were diagnosed as melanosarcomas

Figure 5. A large lower lid papilloma.

that lid masses should be removed or treated prior to onset of clinical symptoms. At the earlier stage, it may be possible to retain both functional and cosmetic lid margin.

8.When is it appropriate to biopsy a mass before excision?

If the mass is extremely ulcerated and extending away from the lid margin, consider biopsy

prior to definitive surgery. The diagnosis may alter the treatment options. An example of this is a large squamous cell carcinoma that may be amenable to therapies other than surgery. If the lesion is less than one-third the length of the eyelid, it is more appropriate to perform an excisional biopsy or biopsy and cryotherapy.

9. How should the tissue be processed?

Tissue that is removed should be placed in an appropriate container with 10% formalin as fixative. If the mass is small, microcassettes can be used to better preserve the tissue and make it easier to process. This is very helpful when tissue specimens are small, and it avoids calls from the laboratory that tissue was misplaced! Even with a treatment modality other than surgical excision, submitting a sample for pathology is still recommended.

10. What are the anatomic considerations when choosing a treatment plan?

There are two main goals to consider when considering treatment alternatives. The first is to preserve mechanical lid function and normal glandular function. Maintaining the lid margin as a mucocutaneous junction is key. The second is the preservation of a cosmetic eyelid. The location of the mass also may be important with regard to the lacrimal puncta. The superior punctum is less important to normal lacrimal flow than the inferior punctum. The latter should be preserved if at all possible to prevent chronic epiphora.

11.What is the most common method of mass removal?

For lesions that constitute less than 25-30% of the lid length, a full-thickness, four-sided

(wedge) resection is the standard technique and provides a functional and cosmetic result by preserving the lid margin completely. The incision is closed in two layers. The subconjunctiva should be closed with an absorbable suture such as 6--0 Vicryl with knots buried. The skin can be closed with a number of suture patterns of 5--0 or 6--0 nonabsorbable suture; generally, an interrupted pattern provides the best results. In darkly pigmented patients, a colored suture such as Prolene is a good choice because it is easy to see. It is important that the lid margins are aligned correctly during this closure and that the suture ends and knots cannot contact the cornea to prevent irritation. An Elizabethan collar is suggested to prevent self-trauma, and suture removal is performed after 2 weeks.

12.What instrumentation do you need for this type of surgery? A basic set of ophthalmic instruments are ideal for lid surgeries.

•Mosquito hemostats X 2

•Castroviejo needle holder

•Steven's tenotomy scissors

•Tissue forceps or Bishop Harmon forceps

•Magnification (either head loop or glasses)

•Optional: Jaeger lid plate, chalazion clamp

13.How do I choose a reconstructive technique if I need one?

In human reconstructive techniques, planning involves consideration of relaxed skin tension

lines (RSTL) and lines of maximum extensibility (LME). In veterinary ophthalmology, attention is paid to skin biomechanics, but there is another factor to consider: the direction of hair growth. Particularly when using flap techniques, it is important to plan with attention to normal hair direction. For inferior lid defects, the primary techniques that have been described include H-plasty

and several rotational flaps. For superior lid defects, there is an increased likelihood of corneal irritation from lid margin, and, therefore, marginal reconstruction becomes more important. Many of the flap techniques that have been described originate in the human literature and have been modified for veterinary ophthalmology. The Table lists some common techniques and areas of lid in which they may be helpful.

14. What other surgical modalities are available for eyelid neoplasms?

For many years, the only other surgical modality used in the treatment of eyelid neoplasia was cryosurgery, which is the use of a freezing agent, typically liquid nitrogen or nitrous oxide, to ablate both normal and abnormal tissue. Recently, however, more and more clinicians are using laser technology to treat lid conditions including neoplasia. The carbon dioxide laser has increased in availability and is now used on a routine basis. The carbon dioxide laser provides not only sharp dissection capability but also generalized ablative function.

15.How does cryosurgery work?

The freezing of tissue causes events at a cellular level that occur in three phases: immedi-

ate, delayed, and late. During the immediate phase, cells are destroyed because of dehydration with concentration of toxic solutes, formation of both intracellular and extracellular ice crystals, denaturation of proteins, and direct thermal shock. In the delayed phase, cellular destruction occurs because of vascular stasis resulting in thrombosis, ischemia, and cell death. Finally, in the late phase, there may be an immunologic, response to freezing with formation of antibodies to the altered tumor cells. Normal cells tend to show increased resistance to the above effects, and, therefore, there is a sparing effect of normal tissue. Isolation of the local blood supply will increase the effectiveness of this technique particularly in highly vascular tissues such as the eyelid.

16.How is cryosurgery performed?

The most common cryogen used in veterinary medicine is liquid nitrogen which has a tem-

perature of -195.8°C. The most common delivery device is a hand-held unit such as the Cryogun (Brymill Corporation), but others are also available. There are a variety of probes available. Both spray and solid probe tips can be used, although spray tips will often result in more rapid freezing of tissue. If solid tips are used, the size should be approximately the size of the lesion to ensure a rapid freeze. In general, the goal is to freeze the tissue to -80°C or below for a duration of I minute or more to induce cryonecrosis. A rapid freeze and slow thaw are optimal. If possible, the lesion should be debulked (often tissue for biopsy is removed during this process). The lesion should be treated for two to three freeze/thaw cycles. Thermocouples are ideal to measure tissue temperature. One can also use the size of the ice ball to gauge the depth of freeze. The visual advancing of the ice ball only represents oac, and therefore only 75% of the visible ice ball is likely to be at optimal temperature. In general, an area of 5-10 mm of normal tissue would be desirable for most malignancies. Remember that the ice ball formation is three dimensional and the depth of freeze should be monitored closely in order to prevent freezing the tissue too much or too little. Probe freezing is less lethal but easier for persons inexperienced with these techniques. The probe can be applied directly to the tumor for contact freezing. If the lesion is circu-

Figure 7. A close-up of a hand piece containing sensors for temperature. The monitor in the background shows temperature in celsius and cylinder pressure.

cell carcinoma. Cisplatin, carboplatin, and 5-fluorouracil (5Pu) have been used mostly in feline patients, but the technique may also be applicable to canine patients with varying success. In addition, some anecdotal reports exist of using intralesional injection of distilled water as a treatment modality of mast cell tumor.

19.Are there any other treatment modalities available?

Yes. Radiation therapy, brachytherapy, and radiofrequency hyperthermia are all acceptable

treatment modalities, although their use has declined in recent years, most likely because of earlier diagnosis and treatment of eyelid neoplasms. Radiation therapy, in particular, can cause severe ocular damage; its use should be considered carefully, and it is indicated only in the event of aggressive neoplasms that are difficult to treat with other modalities (e.g., fibrosarcoma). Photodynamic therapy is a relatively new technique where a photosensitizing chemical is administered systemically and preferentially retained by the tumor. The site is then irradiated with wavelengths absorbed by the chemical. This technique can be used only in superficial tumors and is still in early stages of clinical use.

20.Should enucleation ever be considered when treating eyelid neoplasia?

The goal of any treatment should be to preserve the function and cosmesis of the eye when-

ever possible. However, if a tumor is malignant and too large in size to allow for sparing of ocular function. then enucleation should be considered in an attempt to prevent systemic disease. Such a decision should not be made without a diagnosis of the mass and possibly evaluation by a specialist, particularly if the patient is monocular. The most common tumor requiring enucleation that this author has seen is eyelid fibrosarcoma because often radiation therapy will be required.

BIBLIOGRAPHY

I. Gelatt KN: Veterinary Ophthalmology, 3rd ed. Philadelphia, Lippincott Williams & Wilkins, 1998, pp 558-567.

2.Hamilton HL. Whitley RD. McLaughlin SA. et al: Basic blepharoplasty techniques. Comp Cont Educ Pract Vet 21:946-952. 1999.

3.Roberts SM, Severin GA. Lavach JD: Prevalence and treatment of palpebral neoplasms in the dog: 200 cases (1975-1983). J Am Vet Med Assoc 189:1355-1359, 1986.

4.Ruslander D, Kaser-Hotz B, Sardines JC: Cutaneous squamous cell carcinoma in cats. Comp Cont Educ PractVet 19:1119-1129, 1997.

8. What is panophthalmitis?

Uveal tract inflammation coupled with scleral and corneal inflammation is termed panophthalmitis, It is difficult to maintain a normal-appearing globe with inflammation of this severity and distribution, Preserving vision is hopeless (Fig, 4).

Figure 4. Chronic panophthlamitis in a dog, Note the severe neovascularization of the cornea and the periocular inflammation,

9.What are the major clinical signs of uveitis?

Anterior uveitis typically causes a painful eye with conjunctival and episcleral hyperemia.

miosis, aqueous flare and cell accumulation, corneal edema, iris swelling and hyperemia, and reduced intraocular pressure (hypotony). Vision is impaired but rarely lost with simple anterior uveitis. Vision loss indicates more extensive ocular tissue damage and usually occurs with increased severity or duration of inflammation. An ophthalmoscope is required for assessment of posterior uveitis. Ophthalmoscopic signs include loss of the normal tapetal color, retinal detachment, subretinal transudation or exudation, and loss of retinal pigment epithelial cell and choroidal pigmentation. Posterior uveitis almost always also involves the retina (chorioretinitis) and may cause blindness.

10. Can the clinical signs be used as an indication of chronicity, severity, or prognosis?

The spectrum and magnitude of signs depend on the severity of insult. The Table differentiates acute versus chronic anterior uveitis based on clinical signs. If trauma, vasculitis, or bleeding disorders are underlying causes of uveitis, hyphema and anterior chamber fibrin clots are common. Septic or neoplastic disorders also can induce the above changes and are often bilateral with varying degrees of hypopyon (white blood cells within the aqueous humor) or keratic precipitates (white blood cells and fibrin adherent to the corneal endothelial surface). Posterior uveitis warrants a guarded prognosis for vision. Acute signs include retinal edema, retinal hemorrhage, loss of normal tapetal color, subretinal fluid accumulation, and decreased vision. Chronic signs consist of hyperreflective areas in the tapetal fundus (caused by retinal atrophy and thinning), abrupt color changes of the tapetum, and pigment proliferation or loss (Figs. 5-7).