How to differentiate between choroidal nevus and choroidal melanoma

A 64-year-old woman was referred for consultation regarding a pigmented fundus lesion. She was asymptomatic and enjoyed good vision and systemic health. She took no medications, had no history of ocular trauma or surgeries, and did not admit to a family history of ocular or systemic disorders.

Visual acuity was correctable to 20/20 in each eye. The anterior segments and intraocular pressures were within age-appropriate norms. The significant view of the ocular fundus is shown in Figures 1 to 4.

Discussion

Choroidal nevus (CN) is a frequently encountered pigmented lesion. CN is characterized as having a slate-gray coloration, flat consistency, and somewhat distinct borders.

The most common differential diagnoses include congenital hypertrophy of the retinal pigment epithelium (CHRPE) and small malignant melanoma. (See more on CHRPE in “Diagnosing CHRPE Lesions Can Be a Challenge for ODs” in the June 2017 issue of Optometry Times®.) Distinct differences from CN include jet black color and presence when viewed with red-free light.

Small choroidal melanomas have been described as having certain characteristics by the mnemonic TFSOM (To Find Small Ocular Melanoma).1 Multimodal imaging shows these features, including thickness less than 2 mm, subretinal fluid, vision loss via Snellen acuity, orange pigment, melanoma hollowness on ultrasound/ margin (< 3 mm from optic nerve head), and diameter less than 5 mm.1,2

One simple clinical observation for differentiating CHRPE from CN is based on anatomy. Melanin absorbs red-free light of 540 nm.3 Therefore, structures deep in the retinal pigment epithelium are rendered invisible, or their visibility is significantly attenuated using such a filter. Often neglected in clinical observations and documentation by color fundus photography is that the red-free filter attenuates resolution.3 For this reason, illumination must be increased to preserve the clinician’s ability to view choroidal nevi.

Another potential differential diagnosis of CN is categorized as suspicious nevus. Although this has been somewhat obviated by the TFSOM paradigm, it remains an intermediate classification between CN, which is benign and unlikely to transform to malignant melanoma.^4,5

Conclusion

With the availability of multimodal imaging techniques beyond color fundus photography such as optical coherence tomography and ultrasound, identification and management of pigmented fundus lesions can be made clinically.

References

1. Shields CL, Dalvin LA, Ancona-Lezama D, et al. Choroidal nevus imaging features in 3806 cases and risk factors for transformation into melanoma in 2355 cases: the 2020 Taylor R. Smith and Victor T. Curtin lecture. Retina. 2019;39(10):1840- 1851. doi:10.1097/iae.0000000000002440

2. Shields CL, Kels JG, Shields JA. Melanoma of the eye: revealing hidden secrets, one at a time. Clin Dermatol. 2015;33(2):183-196. doi:10.1016/j.clindermatol.2014.10.010

3. Bennett TJ. Monochromatic fundus photography. Ophthalmic Photographers’ Society. Accessed May 10, 2021. https://www. opsweb.org/page/monochromatic

4. Chien JL, Sioufi K, Surakiatchanukul T, Shields JA, Shields CL. Choroidal nevus: a review of prevalence, features, genetics, risks, and outcomes. Curr Opin Ophthalmol. 2017;28(3):228- 237. doi:10.1097/ICU.0000000000000361

5. Shields CL, Furuta M, Berman EL, et al. Choroidal nevus transformation into melanoma: analysis of 2514 consecutive cases. Arch Ophthalmol. 2009;127(8):981-987. doi:10.1001/ archophthalmol.2009.151