Choroidal Nevus – Understanding the Eye Freckle Inside the Retina

A choroidal nevus is a common, benign growth of pigmented cells in the choroid layer of the eye, often described as an “eye freckle” inside the retina. While most choroidal nevi are harmless and never cause symptoms, they require regular monitoring because a small percentage can transform into melanoma. In this comprehensive guide from the Identify Skin Team, we explore the characteristics, diagnosis (including the choroidal nevus ICD-10 code), and distinctions from similar lesions like iris nevus and retinal nevus.

What Is a Choroidal Nevus?

A choroidal nevus is a cluster of melanocytes (pigment-producing cells) located in the choroid, the vascular layer between the retina and the sclera. It appears as a flat or slightly elevated, grayish to brown lesion on fundoscopic examination. Choroidal nevi are extremely common, occurring in up to 10% of the Caucasian population, and they are typically unilateral. Most are discovered incidentally during routine eye exams.

The term “nevus” (plural: nevi) refers to a benign proliferation of melanocytes, similar to a mole on the skin. When located in the eye, these nevi can be found in different parts: the choroid (choroidal nevus), the iris (iris nevus), or the retina (retinal nevus). Though they share a similar cellular origin, their clinical presentation and risk profiles differ.

Choroidal Nevus ICD-10 Code

For medical documentation and billing, the choroidal nevus ICD-10 code is D31.39. This code falls under “Benign neoplasm of unspecified part of choroid.” If the laterality is specified, codes D31.31 (right eye) and D31.32 (left eye) are used. Accurate coding is essential for tracking patient outcomes and ensuring appropriate follow-up. Clinicians should also document whether the lesion is suspicious or stable.

How Is a Choroidal Nevus Diagnosed?

Diagnosis is primarily clinical, using dilated fundus examination. Key features of a typical choroidal nevus include:

• Flat or slightly elevated lesion with well-defined margins
• Color ranging from slate gray to brown
• Size usually less than 5 mm in diameter and less than 1 mm in thickness
• No associated subretinal fluid or orange pigment (which would raise suspicion for melanoma)
• Drusen overlying the lesion are common and indicate chronicity

Imaging techniques such as optical coherence tomography (OCT) and fundus autofluorescence can help differentiate a benign nevus from a malignant melanoma. Ultrasound may be used to measure thickness and evaluate internal reflectivity.

Risks and Complications

While the vast majority of choroidal nevi are benign, there is a small risk of transformation into choroidal melanoma. Factors that increase risk include:

• Thickness greater than 2 mm
• Subretinal fluid
• Orange pigment (lipofuscin) on the lesion surface
• Symptoms such as flashes, floaters, or vision loss
• Growth documented on serial exams
• Ultrasound hollow (low internal reflectivity)

If any of these features are present, the lesion is considered “suspicious” and requires more frequent monitoring or referral to a ocular oncologist. The mnemonic “To Find Small Ocular Melanomas Using Helpful Hints” (TFSOMUHH) is often used: Thickness >2 mm, Fluid (subretinal), Symptoms, Orange pigment, Margin within 3 mm of disc, Ultrasound hollow, Halo absence, Halo presence (drusen) – actually drusen are protective. The absence of drusen and halo can be worrisome.

Distinguishing Choroidal Nevus from Iris Nevus and Retinal Nevus

The eye can have nevi in different layers, each with unique characteristics:

• Iris nevus: Located on the iris (the colored part of the eye). It appears as a pigmented spot that may be flat or slightly elevated. Iris nevi are generally harmless but should be monitored for growth, thickness, or distortion of the pupil. They are often visible to the patient or observer without special instruments.
• Retinal nevus: Actually, true retinal nevi are rare. Most “retinal nevi” are actually choroidal nevi that are visible through the transparent retina. However, there is a condition called congenital hypertrophy of the retinal pigment epithelium (CHRPE) that is often mistaken for a retinal nevus. CHRPE is a flat, well-defined, dark lesion with a distinct border, usually stable.
• Choroidal nevus: As discussed, it lies beneath the retina and is only visible on dilated fundus exam. It is the most common intraocular nevus.

While iris nevus and retinal nevus (or CHRPE) are usually benign, all pigmented ocular lesions warrant periodic evaluation by an ophthalmologist to rule out malignant transformation.

Management and Follow-Up

Most choroidal nevi require no treatment but need lifelong surveillance. The standard follow-up schedule is:

• Typical nevus: Annual dilated eye exam with fundus photography and OCT.
• Suspicious nevus: Every 3-6 months initially, then annually if stable. Referral to a specialist may be needed.
• Growing or symptomatic lesion: Immediate referral to an ocular oncologist for possible treatment, such as radiotherapy (plaque brachytherapy) if it becomes melanoma.

It is important for patients to be aware of their choroidal nevus and to report any visual changes promptly. There is no known way to prevent a choroidal nevus from forming, but protecting the eyes from ultraviolet light may reduce the risk of ocular melanoma in general.

Conclusion

A choroidal nevus is a common intraocular lesion that is usually benign but requires monitoring. Understanding its characteristics, the appropriate choroidal nevus ICD-10 code, and how it differs from an iris nevus or retinal nevus can help patients and clinicians manage these eye freckles effectively. The Identify Skin Team emphasizes regular eye exams and awareness of risk factors to detect any malignant changes early. If you have a pigmented lesion in your eye, ask your eye doctor for a comprehensive evaluation and a personalized follow-up plan.