Issue 1: Lesions in the fundus (March 2011)

Eye Condition Spotlight: Choroidal Naevi & Melanoma

Choroidal naevi are the most common type of benign intraocular lesions, occurring in around 10 per cent of the general population(2-4). They comprise a large number of spindle cell melanocytes, and around 90 per cent are posterior to the equator. Most develop during the teenage years, when ocular pigment content increases, and less commonly during adulthood. Some display detachment of the retinal pigment epithelium or choroidal neovascularisation, and lesions can be amelanotic(2).

Ultrasound of a choroidal naevi will show a flat or slightly elevated lesion with high internal reflectivity(2-4). OCT studies have further characterised a choroidal naevi as follows:

• Displaying a high rate of hyporeflectivity (pigmented naevi);
• Overlying retinal oedema;
• Subretinal fluid;
• Retinal thinning;
• Photoreceptor attenuation; and
• Occasional RPE detachment(7).

As a result, naevi can lead to visual disturbance.

Management of small naevi requires careful documentation to clearly establish any progression, an imaging service that CFEH specialises in. The initial assessment should include stereoscopic fundus examination and colour imagery. The follow-up assessment, four to six months later, will analyse any growth. If the naevi remains stable the patient should then be monitored with examinations every six to twelve months(4).

Table 1: Risk factors for small tumour progression(2-4,6,8,10)

Large naevi, or those containing suspicious features (Table 1), may warrant baseline fundus photography, combined with ultrasonography and OCT assessment. The patient should be reviewed again within three to four months, and then four to six months if no change, tapering to a 12 month cycle as the stability of the lesion is confirmed4. The growth potential of malignant tumours requires a short initial review, and such cases need a low threshold for referral to an ophthalmologist or CFEH for further assessment. The cumulative growth rate of untreated small choroidal melanomas from the Collaborative Ocular Melanoma Study (COMS) was 11 per cent after one year, 21 per cent after two years and 31per cent after five years(1).

When malignancy is suspected immediate referral to an ophthalmic oncologist is recommended. The greater the number of risk factors identified in the patient (Table 1), the higher the likelihood of malignancy(2).

Although the prevalence of naevi is around 10 per cent, the rate of conversion to melanoma is low and is estimated to be almost one in 9,000(9). With a population of approximately seven million in New South Wales, this means that of the estimated 700,000 cases of naevi, epidemiological data predicts that 79 will convert to melanomas per annum. A self audit of your clinical records will determine if the approximated 10 per cent naevi detection rate has been achieved. A long-term prediction of naevi-tomelanoma conversion rate can also be calculated.

Choroidal melanoma is the most common primary intraocular malignancy in adults (particularly in Caucasians) and accounts for 90 per cent of all uveal melanomas2. Two major cell types have been identified: spindle and epithelioid(2-4).

The COMS definition of melanoma for lesions less than 5mm in diameter (longest axis) and 1mm thickness, without associated risk factors, is a choroidal naevi (Table 2). However, distinguishing a benign naevus from a small melanoma remains challenging(3,5).

Table 2: COMS classification of tumour by size(3)

The risk factors identified in Table 1 should be carefully considered, and an ultrasound that shows low internal reflectivity and shifting of subretinal fluid, with positional changes of patient’s head, is also indicative of malignancy.

Tumours that fall within the COMS classification and smaller lesions with high risk factors should be referred to an ophthalmic oncologist for assessment. Treatment may include transpupillary thermotherapy, charged particle therapy, episcleral plaque brachytherapy or enucleation(2,3).