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Choroidal Nevus and Malignant Melanoma of the Choroid

URGENT — Retina

Symptoms

  • Usually asymptomatic; often an incidental finding during a dilated exam.
  • Photopsias (flashes) if associated subretinal fluid is present.
  • Decreased visual acuity if the lesion is subfoveal or causes complications.
  • Floaters or visual field defects (rare).

Clinical Findings

Choroidal nevus

  • Most common intraocular tumor (present in 5–10% of adults).
  • Appearance: Flat or minimally elevated (<2 mm thick); pigmented or amelanotic; oval or round.
  • Overlying drusen: A benign marker of chronicity and stability.

Choroidal melanoma

  • Most common primary intraocular malignancy in adults.
  • Shape: Dome-shaped pigmented mass; may rupture Bruch membrane to form a pathognomonic mushroom or collar-button configuration.
  • Surface features: Orange lipofuscin (hyperautofluorescent) and surrounding subretinal fluid indicating activity.

Ultrasound signatures

  • B-scan: Acoustic hollowness (low-to-medium internal reflectivity), choroidal excavation (scooped dip beneath tumor), and orbital shadowing.
  • A-scan: Initial high spike followed by a descending angle with low-medium internal reflectivity.

Imaging (OCT & faf)

  • OCT (EDI): Highly sensitive for detecting small amounts of subretinal fluid (a critical risk factor) and overlying retinal changes.
  • FAF: Orange pigment (lipofuscin) appears hyperautofluorescent; drusen over nevi appear relatively hypoautofluorescent.

Risk assessment (tfsom-uhhd mnemonic)

  • T — Thickness >2 mm (measured by B-scan).
  • F — subretinal Fluid (detected by OCT).
  • S — Symptoms (vision loss, flashes, or floaters).
  • O — Orange pigment (lipofuscin; hyperAF).
  • M — Margin within 3 mm of the optic disc.
  • U — Ultrasound hollowness (low internal reflectivity).
  • H — Halo absent (presence of a halo suggests benignity).
  • D — Drusen absent (presence of drusen suggests benignity).
  • Growth risk (5-year): 0 factors ≈ 3%; 3 factors ≈ 25%; ≥5 factors ≈ >50%.

Metastatic biology

  • Hematogenous spread occurs primarily to the liver (>90% of cases).
  • Prognostication (GEP): Class 1A (best, ~2% risk), Class 1B (intermediate), Class 2 (highest risk, ~50% at 5 years).

Etiology

General

  • Choroidal nevus: Benign melanocytic proliferation.
  • Choroidal melanoma: Primary intraocular malignancy often arising from a pre-existing nevus.

Transformation risk

  • Risk factors for malignancy: Thickness >2 mm, subretinal fluid, symptoms, orange pigment, margin near disc, and absence of drusen/halo.

Patient risk factors

  • Fair skin, light irides, and oculodermal melanocytosis (nevus of Ota; 1/400 lifetime risk).
  • Dysplastic-nevus syndrome and germline BAP1 mutations.

Genetic markers

  • Monosomy 3, 8q gain, and BAP1 loss correlate with high metastatic risk.

Red Flags

  • Any "tfsom-uhhd" risk factors: Presence of two or more warrants urgent oncology referral.
  • Rapid growth or new internal vascularization.
  • Hepatomegaly or abnormal LFTs at diagnosis: Suggests existing metastatic disease.
  • Class 2 gene expression profile or monosomy 3: Indicates 50% metastatic risk at 5 years.

Investigations

Clinical exam

  • Dilated fundus examination with 20D lens; detailed clinical drawing.
  • Baseline color fundus photography to track diameter and growth.

Multimodal imaging

  • B-scan and A-scan ultrasound: To determine thickness and acoustic reflectivity.
  • EDI-OCT: To detect subtle subretinal fluid and retinal disruption.
  • Fundus Autofluorescence (FAF): To identify orange pigment (lipofuscin).

Systemic & biopsy

  • Fine-needle aspiration: For cytogenetics/GEP prognostication (selected cases).
  • Metastatic workup: LFTs, LDH, and liver MRI (preferred) or ultrasound every 6–12 months.

Treatment

Nevus management

  • Serial observation with multimodal imaging to confirm stability.

Melanoma treatment

  • Plaque brachytherapy (I-125 or Ru-106): First-line for globe preservation in most small-to-medium tumors.
  • Proton-beam or stereotactic radiotherapy: Used for juxtapapillary lesions.
  • Enucleation: Reserved for large tumors or eyes with no visual potential.
  • Exenteration: Indicated only for cases with orbital extension.

Adjuvant therapy

  • Intravitreal anti-VEGF: Every 4 months for 2 years post-radiation to minimize radiation retinopathy.

Metastatic surveillance

  • Lifelong monitoring of the liver (LFTs, LDH, MRI) every 6–12 months.

Clinical Pearl

The "tfsom-dim" (or uhhd) mnemonic flags a nevus at risk: thickness, fluid, symptoms, orange pigment, margin near disc, diameter, and absent drusen/halo. Two or more features warrant oncology referral.

Differential Diagnosis

  • Congenital hypertrophy of the RPE (CHRPE)
  • Choroidal hemangioma
  • Choroidal metastasis
  • Choroidal osteoma
  • Amelanotic choroidal melanoma

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