Iris Melanoma

From EyeWiki



Disease Entity

Iris melanoma is the most common primary neoplasm of the iris and account for approximately 5% of all uveal melanomas. The average age of involvement lies within the 5th decade. Although there is no gender predilection, iris melanomas occur more frequently in Caucasians with a light colored iris versus non-Caucasions. There is no consistent evidence linking iris melanoma with UV light or environmental exposure


Diagnosis

Most iris melanomas are asymptomatic and thus diagnosed at an ophthalmic routine examination. In addition to a circumscribed or diffuse iris mass, heterochromia, chronic uveitis, glaucoma, or spontaneous hyphema may occur.

Clinical diagnosis

Clinically, circumscribed (Fig. 1A) and diffuse (Fig. 2A) iris melanomas can be distinguished.

Iris melanomas are mainly located in the anterior border layer and most of them arise from nevi. They vary in size, shape, and clinical behavior. Due to the amount of pigment iris melanomas can appear whitish, tan, or dark brown. An irregular surface, prominent vessels and tumor growth are observed in more aggressive lesions. They can be accompanied by a sectoral cataract, corectopia or ectropion uveae. Heterochromia (with a darker iris) can be a sign of diffuse melanoma. Secondary glaucoma can develop due to direct infiltration of the chamber angle with resultant circumferential growth, pigment dispersion (melanomalytic glaucoma), or lens displacement. Photo-documentation and ultrasound examination (Fig. 3A, B) should be obtained as a baseline value and on follow-up visits to document changes in size and shape.

Modern imaging techniques comprise also anterior segment optical coherence tomography. Examinations should also include - besides a thorough slit-lamp exam with measurement of the intraocular pressure - transillumination, gonioscopy, and a detailed fundus exam with scleral depression. Fine needle aspiration biopsy (FNAB) may be useful to obtain an incisional or excisional biopsy for diagnostic purposes (in unclear cases). Screening for metastasis is also highly recommended once the tumor reveals a more aggressive clinical appearance and behavior.

Histologic diagnosis

Most iris melanomas are composed of spindle cells (Fig. 1B, C) and are, therefore, regarded as  low-grade tumors.

More aggressive iris melanomas (Fig. 2B) exhibit a varying amount of epitheloid cells. The amount of pigment also varies among lesions.
Figure 2B: Histopathologic examination reveals a heavily pigmented tumor composed of spindle B and epitheloid cells as well as melanomacrophages

Differential diagnosis

  • Iris freckle
  • Iris nevus
  • Iris melanocytoma
  • Iris nevus syndrome
  • Iris pigment epithelial cyst
  • Peripheral anterior synechiae
  • Iris foreign body
  • Lisch nodules
  • Fuch’s heterochromic iridocyclitis
  • Latanoprost therapy
  • Juvenile xanthogranuloma
  • Iris metastases
  • Leukemia
  • Ciliary body melanoma with anterior extension
  • Other iris tumors (e.g. leiomyoma, rhabdomyosaroma)

Management

Treatment

The treatment strategy of iris melanomas depends on the clinical impression and behavior. Small non-growing lesions may be just periodically observed (“watchful waiting”) and thoroughly documented. If the clinical behavior is more worrisome with a lesion exhibiting documented growth, surface nodularity, and prominent vascularity, different treatment options are available such as brachytherapy (as primary or secondary procedure), excisional biopsy (FNAB or iridectomy with anterior cyclectomy if needed), and enucleation. The latter procedure is reserved for a diffuse involvement of the iris and angle structures or the development of complications like glaucoma that are not amenable to non-invasive methods.

Follow up

Periodical follow-up is required in order to document the growth pattern of the mass or to evaluate the outcome after treatment.

Prognosis

Iris melanomas are more indolent and exhibit a lower metastasis rate then their ciliary body or choroidal counterparts. The rate of metastasis is approximately 3% at 5 years, 5% at 10 years, and 10% at 20 years.

Additional Resources

References

  1. Shields CL, Shields JA, Materin M, Gershenbaum E, Singh AD, Smith A. Iris melanoma: risk factors for metastasis in 169 consecutive patients. Ophthalmology. 2001;108(1):172-8.
  2. Spencer WH. Ophthalmic Pathology. An Atlas and Textbook (4th edition). Philadelphia: WB Saunders; 1996.
  3. Yanoff M, Sassani JW. Ocular Pathology (6th edition). Elsevier; 2009.