CHAPTER 17

Melanocytic Tumors

Introduction

Intraocular melanocytic tumors arise from the uveal melanocytes in the iris, ciliary body, and choroid. In contrast to melanocytic tumors of the skin and mucosal membranes, which develop in ectodermal tissue and usually spread through the lymphatics, uveal melanocytic tumors arise in mesodermal tissue and typically disseminate hematogenously, if there is metastatic spread.

There are 2 groups of melanocytic tumors of the uvea: the benign nevi and the melanomas. Pigmented intraocular tumors that originate in the pigmented epithelium of the iris, ciliary body, and retina constitute another group of melanocytic tumors. These rare tumors are discussed separately at the end of this chapter. See also Chapter 12.

Iris Nevus

An iris nevus generally appears as a darkly pigmented lesion of the iris stroma with minimal distortion of the iris architecture (Fig 17-1). The true prevalence of iris nevi remains uncertain because many of these lesions produce no symptoms and are recognized incidentally during routine ophthalmic examination. Iris nevi may present in 2 forms:

circumscribed iris nevus: typically nodular, involving a discrete portion of the iris diffuse iris nevus: may involve an entire sector or, rarely, the entire iris

In some cases, the lesion causes slight ectropion iridis and sectoral cataract. The incidence of iris nevi may be higher in the eyes of patients with neurofibromatosis.

Figure 17-1 Iris nevus, clinical appearance. The lesion is only slightly raised from the iris surface, and lesion color is homogeneous brown.

Iris nevi are best evaluated by slit-lamp biomicroscopy coupled with gonioscopic evaluation of the angle structures. Specific attention should be given to lesions involving the angle structures to rule out a previously unrecognized ciliary body tumor. The most important possibility in the differential diagnosis of iris nevi is iris melanoma. When iris melanoma is included within the differential diagnosis, close observation with scheduled serial follow-up examinations is indicated. Clinical evaluation of suspicious iris nevi should include slit-lamp photography and high-frequency ultrasound biomicroscopy. Iris nevi usually require no treatment once they are diagnosed, but, when suspected, they should be followed closely and photographed to evaluate for growth.

Nevus of the Ciliary Body or Choroid

Nevi of the ciliary body are occasionally incidental findings in histopathologic examination of globes that are enucleated for other reasons. Choroidal nevi may occur in up to 10% of the population. In most cases, they have no clinical symptoms and are recognized on routine ophthalmic examination. The typical choroidal nevus appears ophthalmoscopically as a flat or minimally elevated, pigmented (gray-brown) choroidal lesion with indistinct margins (Fig 17-2). Some nevi are amelanotic and may be less apparent. Choroidal nevi may be associated with overlying RPE disturbance, drusen, serous detachment, choroidal neovascular membranes, and orange pigment; and

they may produce visual field defects. On fluorescein angiography, choroidal nevi may either hypofluoresce or hyperfluoresce, depending on the associated findings. Ocular and oculodermal melanocytosis may predispose to uveal malignancy, with an estimated lifetime risk of 1 in 400 in the white population. Choroidal nevi are distinguished from choroidal melanomas by clinical evaluation and ancillary testing. No single clinical factor is pathognomonic for benign versus malignant choroidal melanocytic lesions. The differential diagnosis for pigmented lesions in the ocular fundus most commonly includes the following:

choroidal nevus choroidal melanoma

atypical disciform scar associated with age-related macular degeneration (AMD) suprachoroidal hemorrhage

RPE hyperplasia

congenital hypertrophy of the retinal pigment epithelium (CHRPE) choroidal hemangioma with RPE hyperpigmentation melanocytoma

metastatic carcinoma with RPE hyperpigmentation choroidal osteoma