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Iris Nevus vs Melanoma

By Dr. Liji Thomas, MD

Iris tumors are not very common. They may be classified as solid or cystic tumors. Among the solid tumors, iris nevi and melanomas fall into the melanocytic tumor category. This also includes iris freckle, melanocytoma, and Lisch nodules.

Iris Nevus

An iris nevus appears as a pigmented or unpigmented spot on the iris, typically about 3 mm in diameter at the base. It penetrates deeper into the iris stroma than a freckle would, and produces ectropion or corectopia. The mean age at presentation is 51 years, and the incidence is higher in females.

Signs of Malignant Transformation

An iris nevus which is suspicious for malignancy may show signs of frank malignancy in 4 of every 100 patients within 10 years, which increases to 11% by 20 years. Signs which indicate the risk of malignant transformation of an iris nevus include:

  • Age below 40 years
  • The presence of hyphema, or blood in the anterior chamber (3%)
  • Diffuse pattern of growth extending all around the rim of the iris, leading to the formation of a ring melanoma
  • Feathery outline
  • The presence of ectropion (45%) or corectopia (24%)
  • The location of the tumor on the inferior half of the iris
  • Involvement of the angle of the anterior chamber, or the iridocorneal angle, by tumor cells growing into the root of the iris into the anterior chamber
  • Tumor seeding on to the iris stroma
  • Tumor growth into the lens, producing subluxation of the lens, astigmatism, or opacity of the lens, either sectoral or diffuse
  • Secondary glaucoma due to tumor infiltration into the trabeculae, or anterior displacement of the iris
  • Breakdown of the communication between the ciliary epithelium and the iris, with resulting decrease in the production of aqueous humor in the anterior chamber, and a low intraocular pressure

Iris Melanoma

An iris melanoma is a malignant tumor which can show local extension and metastasis, and can lead to death. This tumor occurs most often in middle age. Approximately half of them are located in the inferior quadrant, and the mean base diameter was 6.2 mm. The average thickness of an iris melanoma is 2.3 mm, and the great majority (90%) are completely or partially pigmented. Their appearance, thus, ranges from off-white to dark brown. Secondary glaucoma is present in more than a third of such cases. Most of the malignancy-specific features increase in incidence with age.

Features of metastasis include extraocular involvement by anterior growth, and increased intraocular pressure.

Diagnosis and Treatment

It is notoriously difficult to distinguish between a nevus and an early melanoma. Thus, small circumscribed lesions may be followed up over time to check for progressive growth, which is the hallmark of a melanoma.

The use of ultrasonography will delineate the size of the lesion, its thickness, position and extent. It can help distinguish some features of the melanoma, such as a low internal reflectivity, solid pattern and increased vascular pulsations. On the other hand, a well-defined melanoma which extends over less than 3-4 clock hours without iridocorneal extension or extraocular spread can be resected. More than half of anterior (iris) melanomas belong to this category. Large tumors which show evidence of seeding are treated by plaque radiotherapy. Elevated intraocular pressure, which cannot be brought under treatment, is an indication for enucleation of the eye.

Reviewed by Susha Cheriyedath, MSc

References

Further Reading

Last Updated: Aug 31, 2016

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