Use imaging to distinguish nevus from melanoma

NEW ORLEANS – Ocular melanoma can lead to death, but optometrists can make an early diagnosis by using ultrasound, autofluorescence, fundus photography and optical coherence tomography.

Carol Shields, MD, co-director of the oncology service at Wills Eye Hospital in Philadelphia, explained how to distinguish choroidal nevus from ocular melanoma during the plenary session here at the American Academy of Optometry Meeting. Primary Care Optometry News partially sponsored the session.

Carol Shields

“You need to know which nevus is going to turn into melanoma,” Shields began. “Sometimes it’s simple, and sometimes it’s very challenging.”

Choroidal nevus occurs in about 5% of all patients in the posterior segment, but can be found in up to 20% if you extrapolate to the entire fundus, she said.

Prevalence increases with age. Eight percent of people older than 80 years have a nevus, which is probably one patient per day in your practice, she said.

Most patients have no symptoms, Shields continued. Seventy-four percent of nevi are pigmented, 9% have some subretinal fluid, and 6% have overlying orange pigment.

“These factors predict the growth of nevus into melanoma,” she said.

Shields shared some more statistics: choroidal nevus and its features change over time; they can affect vision, especially if subfoveal; and they can enlarge and still remain a nevus.

“You can assure your patients that less than 1% turn into melanoma,” she said.

She continued: Tumors are thicker in older patients, there is usually more than 1 nevus per eye in older patients, and most older patients have underlying drusen. Twenty-six percent of cases show at least three lines of subfoveal vision loss over 20 years, and many of these patients develop retinal pigment epithelium atrophy and cystoid macular edema.

The risk for transformation of nevus to melanoma is 1 in 269,000 in patients between 15 and 19 years old, but 1 in 3,000 in patients 70 to 74 years old.

“If we presume every melanoma originates from a nevus, 1 in 8,845 nevi might turn into a melanoma,” she said. “But between 50 and 80 years old, they’re at high risk for transformation.”

Shields shared a mnemonic to help clinicians remember risk factors for transformation: “To find small ocular melanoma using helpful hints daily.”

thickness greater than 2 mm

fluid (subretinal)

symptoms

orange pigment present

margin within 3 mm of the optic disc

ultrasound hollow

halo absent

drusen absent

“Those 2 mm or less prove to be nevus, and those 3 mm or more prove to be melanoma,” Shields said. “For those 2 mm to 3 mm, use risk factors to make the determination.”

Shields discussed various imaging technologies that can be helpful in differentiating nevi from melanomas.

“Ultrasound is good for measuring thickness,” she said. “OCT for fluid. Take a history for symptoms and use autofluorescence for pigment and ophthalmoscopy for disc, halo and drusen.”

Fundus photography can determine exact margins relative to vessels, Shields said. Ultrasound shows if it is an echodense mass. OCT EDI (enhanced depth imaging) is ideal for younger patients, small nevi and those closer to the equator.

“Shaggy photoreceptors show the detachment is fresh,” she said, “and indicate small melanomas.”

When using autofluorescence, melanoma shows a prominent orange pigment on the surface, Shields said.

“You would never miss this,” she added. “It’s the brightest hyper autofluorescence.”

She cautioned clinicians to beware of imposters.

“Diffuse melanoma can look like nevus,” she said. “OCT can pick up choroidal tumors and subretinal fluid. Choroidal melanocytosis is an imposter.

Congenital hypertrophy of the retinal pigment epithelium is also an imposter.

“I don’t think anyone would miss this,” Shields said. “It does not lead to melanoma.”

Other imposters include combined hamartoma retinal pigment epithelium and subretinal hemorrhage, especially in older patients. – by Nancy Hemphill, ELS, FAAO

Disclosure: No products were mentioned that would require financial disclosure.