TUMORS INVOLVING THE UVEAL TRACT

Several important tumors that may be first identified during ophthalmoscopic examination are discussed below.

Nevus

Nevi (Figures 7-7 and 7-8) are usually flat lesions with or without pigment lying in the stroma of the tissue. On the anterior surface of the iris, they may be noted as iris "freckles." Posteriorly in the choroid, one may see flat pigmented areas. Large choroidal nevi are difficult to differentiate from malignant melanomas. Their flat appearance and especially their lack of growth on repeat serial examinations are important in the differential diagnosis from malignant melanoma.

Because of the difficulties in differentiation from malignant melanomas, fundus photographs or careful line drawings should be made of all suspicious lesions. The elevation or thickness of these lesions can best be measured and documented by ultrasonography. Observations should be made periodically for changes.

Ocular & Oculodermal Melanocytosis

Hyperpigmentation of tissue due to an abundance of large, pigmented uveal melanocytes and episcleral melanocytes occurs in both ocular and oculodermal melanocytosis. Melanocytes located deep in the dermis give the skin around the eye a bluish or slate-gray color in oculodermal melanocytosis. Eyes with melanosis-particularly ocular melanosis, which is most common in Caucasians-have a slightly increased risk of developing uveal and orbital melano-mas.

Hemangioma of the Choroid

Choroidal hemangiomas occur as isolated localized tumors or as diffuse hamartomas associated with Sturge-Weber syndrome. Ultrasonography can help distinguish these orange-colored tumors from amelanotic choroidal melanomas. Visual loss is the result of secondary retinal detachment, degenerative changes in the retinal pigment epithelium or sensory retina, and secondary glaucoma.

Occasionally, choroidal hemangiomas can be treated with photocoagulation to limit the extent and degree of associated serous detachment of the retina. Those that fail to respond to photocoagulation-and especially the more diffuse tumors-may require radiotherapy. Enucleation may be necessary for tumors associated with intractable, painful glaucoma.

Medulloepitheliomas of the Ciliary Body

Benign and malignant medulloepitheliomas are rare tumors that may arise from the ciliary body epithelium, which is the anterior extension of the retina (see Chapter 10), and are therefore not truly tumors of the uveal tract. Those with one or more heteroplastic elements, such as hyaline cartilage, brain tissue, or rhabdomyoblasts, are called teratoid medulloepitheliomas. Those that arise soon after birth may infiltrate the area around the lens and produce a white pupillary reflex similar to that seen in eyes with retinoblastoma.

Malignant Melanoma

It has been estimated that intraocular malignant melanoma occurs in 0.02-0.06% of the total eye patient population in the USA. It is seen only in the uveal tract and is the most common intraocular malignant tumor in the white population. It is almost always unilateral. Eighty-five percent appear in the choroid (Figure 7-9), 9% in the ciliary body, and 6% in the iris.

This tumor may be seen in its early stages only accidentally during routine ophthalmoscopic examination or because of blurring due to macular invasion. Blood-borne metastases may occur at any time. Glaucoma may be a late manifestation.

Histologically, these tumors are composed of spindle-shaped cells, with or without prominent nucleoli, and large epithelioid tumor cells. Tumors composed of the former have a good prognosis; tumors with the latter a poorer prognosis.

Intraocular malignant melanomas may extend into adjacent intraocular tissues or outside the eye through the scleral canals or by intravascular invasion.

Clinical manifestations are usually absent unless the macula is involved. In the later stages, growth of the tumor may lead to retinal detachment with loss of visual field. A tumor located in the iris may change the color of the iris or deform the pupil. Pain does not occur in the absence of glaucoma or inflammation.

The first step in diagnosis is to suspect the lesion. Most intraocular malignant melanomas can be seen ophthalmoscopically. Always suspect the presence of a tumor in eyes with nonrhegmatogenous retinal detachment. A significant incidence of intraocular melanomas has been found in blind, painful eyes; ultrasonography will help detect these.

Enucleation of an eye with a choroidal melanoma has been the traditional treatment. Recently, other forms of therapy, particularly local resection or radiotherapy with charged particles such as helium ions and protons or with plaques of radioactive isotopes sutured to the sclera, have been used for eyes with all but the largest tumors. Very small melanomas (< 10 mm in diameter) have an excellent prognosis and are often impossible to differentiate from benign nevi; therefore, most authorities advocate not treating these tumors until unequivocal growth can be documented (usually with serial photographs or ultrasound measurements). In patients with metastatic disease, the median survival time is less than 1 year, the value of chemotherapy is limited, and treatment to the affected eye is for symptomatic relief only.

Small melanomas of the iris that have not invaded the iris root can be safely observed until growth is documented; then they can be removed by iridectomy. Lesions that invade the iris root and ciliary body can be treated with iridocyclectomy unless the tumor has extended around the trabecular meshwork and Schlemm's canal to form a ring melanoma with secondary glaucoma. Iris melanomas have an excellent prognosis; the mortality rate is less than 1%. Many pigmented iris tumors are actually large nevi rather than malignant melanomas. Iris cysts, traumatic foreign bodies, and inflammatory nodules can also mimic melanomas.

Choroidal Metastases

Because of its rich blood supply, the choroid is an important site for blood-borne metastases. In females, carcinoma of the breast is much the most common source. In males, lung, genitourinary, and gastrointestinal malignancies are the usual primaries. Metastasis to the choroid usually becomes apparent within 2 years after diagnosis of the primary malignancy, but occasionally it does not become manifest until many years later. Occasionally-especially for lung carcinomas-the appearance of a choroidal metastasis may precede the diagnosis of the primary neoplasm.

The usual presenting symptoms of choroidal metastasis are decreased vision and photopsia. The tumor appears as a pale, non-pigmented elevation of the choroid, often associated with serous retinal detachment. There may be multiple lesions involving one or both eyes, in which case the diagnosis is relatively easily made. A solitary metastasis may be mistaken for an amelanotic choroidal malignant melanoma. Ultrasonography and fine-needle biopsy may aid in differentiation.

Chemotherapy for concurrent metastatic disease is usually effective against the choroidal component. In the absence of other metastases, local radiotherapy is the treatment of choice.

10.1036/1535-8860.ch7

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