Blue nevus masquerading as an amelanotic melanoma of the iris: A case report

BACKGROUND Blue nevi are benign lesions characterized by localized proliferation of melanocytes, seen as solitary blue-grey nodules due to light scattering.Amelanotic cellular blue nevus (ACBN) of the iris is an exceptionally rare benign melanocytic lesion that can closely mimic amelanotic uveal melanoma.CASE SUMMARY A 56-year-old male presented with progressive diminution of vision in his left eye for the past year.Corrected distance visual acuity was 4/60.Left eye revealed a vascularized mass at the base of the superior nasal quadrant of the iris, an organized hyphema of 2 mm, dyscoria, cataract and an intraocular pressure of 14 mmHg.The iris lesion was light pink with prominent blood vessels.Ultrasound biomicroscopy delineated a well-defined mass in the iris stroma till the adjacent iridocorneal angle, stopping short of the ciliary body.Contrast-enhanced magnetic resonance imaging confirmed a well-defined 4.1 mm × 3.3 mm × 3 mm lesion in the superonasal aspect of the left globe near the ciliary body, hyperintense on T1-weighted and hypointense on T2-weighted images, with subtle diffusion restriction and homogeneous post-contrast enhancement, suggestive of uveal melanoma.Aqueous cytology was inconclusive.However, excision biopsy of the lesion demonstrated an ACBN.CONCLUSION Current imaging modalities have limited ability to conclusively differentiate between benign and malignant iris lesions.On suspecting a more aggressive condition, the absence of evidence-based protocols often leads to overtreatment.In our case, contrast-enhanced magnetic resonance imaging suggested uveal melanoma, prompting surgical 4 / 25 excision and histopathological corroboration.The present case also contributes to understanding of the natural history of ACBN of the iris.