Neoplasia Ocular
Neoplasia Ocular
Neoplasia Ocular
20
OCULAR NEOPLASIA
Steven John Dugan, DVM, MS
General surveys of equine tumors have shown that the skin, eyes,
and genitalia are most frequently affected by neoplastic conditions. 1, 49
Sarcoid, squamous cell carcinoma (SCC), papilloma, melanoma, nerve
sheath tumors, and lipoma, in descending order of prevalence, are the
most common neoplasms of equidae. 29 , 48, 60 Sarcoids are most common
on the forehead, eyelids, and face;29, 60 sec most commonly involves
the ocular region. 29 , 48, 60 Retrospective studies of tumors affecting the
equine eye, adnexa, and orbit have revealed that sec is most common,
representing 48% to 75% of the tumors. Sarcoid ranks second among
tumors of the equine ocular region (8%-38%). Papilloma, melanoma,
and nerve sheath tumors, combined, represent 7% to 9% of equine
ocular neoplasms; although less frequent, these tumors are the only
other commonly reported neoplasms of the equine ocular regionS, 36
(Dugan SJ, Severin GA, Roberts SM, et aI, unpublished data, 1988).
Thus, literature regarding equine ocular oncology is limited in scope.
As a result, this article briefly reviews general diagnostic modalities
and treatment alternatives available for ocular/periocular neoplasia.
Clinical aspects (prevalence, risk factors, differential diagnosis, treat-
ment, prognosis, and prevention) of specific tumor types affecting the
eyelids, nictitating membrane, cornea, bulbar conjunctiva and/or sclera,
intraocular structures, and orbit also are reviewed.
The age, breed, gender, haircoat and skin color, geographic loca-
tion, husbandry practices, duration of the ocular problem, season in
Diagnostic Work-up
Imaging Techniques
B-scan, two-dimensional ultrasonography is a useful, noninvasive
diagnostic technique that can be used to delineate the extent of intra-
ocular as well as retrobulbar masses. If extensive corneal or lenticular
disease precludes examination of the intraocular structures, the globe
can be examined effectively by ultrasonography. Ultrasonography is
the best method (with the exception of computed tomography and
magnetic resonance imaging) for defining the characteristics (e.g., solid
mass versus cellulitis) of retrobulbar disease. 13
Thoracic radiography should be performed if metastatic disease is
suspected. Conventional skull radiography for diagnostic evaluation of
the equine orbit requires general anesthesia and multiple radiographic
projections or views. Insertion of Flieringa's rings within the conjunc-
tival sacs assists interpretation. The complicated facial anatomy may
conceal identifiable radiologic signs of orbital disease despite adequate
radiographic technique. A special procedure that uses a radiopaque
dye to outline the nasolacrimal system, dacryocystorhinography, can
be used to identify the anatomic location of an obstruction.
TREATMENT
Methods of tumor treatment are determined by the nature of the
primary disease, its biologic behavior, the size and anatomic location
of the lesion, and the presence or absence of distant metastases. In
addition, the skills of the clinician, equipment available, and financial
restrictions imposed by clients may favorably or unfavorably influence
612 DUGAN
Complete Excision
Cryotherapy
Maximum cellular destruction results from a rapid freeze and slow
thaw cycle. Tumors are destroyed as intercellular ice crystals form,
causing dehydration of cells and their constituent organelles. Overall,
the best cryogen is liquid nitrogen. Liquid nitrogen may be applied as
a spray or with a probe tip. Ideally, two or three freeze-thaw cycles
are performed and a thermocouple is used to monitor tissue tempera-
0 0
ture. The tumor's temperature should be decreased to -20 to -30
C. Deep tumor margins should be monitored with thermocouples
because the depth of a freeze is difficult to judge based on the surface
ice ball size. Temporary vascular occlusion by means of clamps (e.g.,
Chalazion clamp) or direct pressure on tumor tissue facilitates freezing.
A freeze margin of normal tissue 5 to 10 mm around the malignancy is
desirable. Following cryosurgery, the acute tissue reaction is profound
and includes swelling, transudation, exudation, and necrosis. Transient
skin depigmentation (vitiligo) and permanent whitening of the hair
(poliosis) occurs. When eyelids are frozen, some contracture occurs;
excessive or repeated treatment therefore may cause blepharophimo-
sis. 35 The advantages of cryotherapy are: It is a simple, rapid, and
inexpensive procedure; it is excellent for suspicious, premalignant
lesions; and it may be repeated.
Hyperthermia
Malignant cells are more sensitive to noncoagulating temperatures
than normal tissue. A tumor's response to heat is governed by its mass
OCULAR NEOPLASIA 613
Strontium 90 ~ Irradiation
Strontium 90 (90Sr) ~ irradiation is primarily used as adjunctive
treatment for corneal and limbal SCC. The irradiation dose fall-off is
rapid, so tissue penetration is not greater than 1 to 2 mm. The usual
dosage is 45 to 100 Gray (4500 to 10,000 rads).35 A sealed probe
containing 90Sr is used by holding the device in direct contact with the
target tissue until the calculated radiation dose is delivered. Retreatment
is possible, but the total accumulated dose should not exceed 200 to
250 Gray. Doses approaching 200 Gray or more cause permanent
radiation damage to normal tissue.
Chemotherapy
An intralesional matrix chemotherapeutic modality for treatment
of SCC in horses has been described. 38 The drug delivery system for
sustained release of 5-fluorouracil and cisplatin is still in the develop-
mental stages. The goal is to obtain high intratumoral drug concentra-
tions for extended periods by the passive association of chemothera-
peutic agents with a high molecular weight matrix. 38 This delivery
system and the antineoplastic drugs incorporated in it are not approved
for use in horses. Proper client informed consent should be obtained
and treated horses prevented from entering the food chain. Parenteral
administration of antineoplastic drugs may be feasible in certain situa-
tions, but the precautions just stated are also applicable.
Immunotherapy
Interstitial Radiotherapy
Sarcoid
Sarcoid is the most common equine tumor, but if only ocular and
periocular tumors are considered, see is the most common. In contrast
to equine ocular and periocular SCC, sarcoid usually affects younger
horses (7 years of age or less) and does not have a predilection for any
breed, gender, or hair coat color. 18, 27 The cause of equine sarcoid
remains uncertain, but two viruses, bovine papilloma virus66 and a
C-type retrovirus,7 have been implicated.
Sarcoids are biologically benign, fibroblastic tumors of the skin
affecting horses, donkeys, and mules. Single or multiple lesions may
develop and grow in a locally aggressive fashion. 39 Sarcoids in the
periocular region are reportedly less aggressive than those appearing
in other locations. 47 Nonetheless, sarcoid affecting an eyelid may stub-
bornly resist treatment and cause marked clinical disease.
Sarcoids have considerable variation in their clinical appearance.
Three morphologic types have been described: (1) Verrucous or wart-
like sarcoid is characterized by a dry, cauliflower-like, hairless lesion,
usually less than 6 em in diameter. (2) Fibroblastic sarcoid often
resembles granulation tissue and may be greater than 20 em in diameter.
And (3) mixed sarcoid is a combination of the first two types. 50
Differential diagnoses should include SCC, fibroma, fibrosarcoma, pap-
OCULAR NEOPLASIA 617
Papilloma
Figure 2. A, This large sarcoid had been injected twice with BCG. Minimal change in the
tumor volume was noted. B, After the third injection, a 75% reduction in volume occurred.
Following the fourth BCG injection, tumor resolution was complete. (Courtesy of S. M.
Roberts.)
618 DUGAN
Melanoma
Cutaneous Habronemiasis
INTRAOCULAR TUMORS
Melanoma
Medulloepithelioma
ORBITAL TUMORS
SUMMARY
Except for two neoplasms, notably see and sarcoid, ocular and
periocular tumors are uncommon in horses. The practitioner must
accurately determine the type of tumor by histopathology so appropri-
ate treatment and a legitimate prognosis can be offered. The first
attempt at treatment has the greatest chance to result in a cure; an
aggressive treatment regimen therefore should be selected from the
start.
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