Occult amelanotic ciliary body melanoma with retinal invasion detected by ultrasound biomicroscopy after nondiagnostic conventional imaging: a case report

Amelanotic ciliary body melanoma is a rare and diagnostically challenging intraocular malignancy that may masquerade as anterior segment inflammation and remain undetected on conventional imaging. A 72-year-old woman presented with unilateral ocular redness, pain, and progressive visual loss despite treatment for presumed uveitis. Examination revealed iris neovascularization, focal iris elevation, localized angle obstruction, and an intraocular pressure of 29 mmHg. Scanning laser ophthalmoscopy, anterior segment optical coherence tomography, B-scan ultrasonography, and orbital magnetic resonance imaging showed no definite intraocular mass. Ultrasound biomicroscopy (UBM) identified an irregular ciliary body lesion measuring 6.03 mm in basal diameter and 1.32 mm in thickness. Local excision confirmed amelanotic melanoma composed predominantly of small round-to-oval cells, with a Ki-67 index of approximately 30%. Postoperative hyphema and refractory ocular hypertension necessitated enucleation. Final pathological examination showed residual melanoma with predominantly epithelioid morphology involving the ciliary body and adjacent choroid, with retinal invasion and a Ki-67 index of approximately 60%. SOX10 and PRAME were positive in both specimens, whereas S100, Melan-A, and HMB45 expression was discordant. No orbital recurrence or distant metastasis was detected during 12 months of follow-up. UBM enabled detection of an otherwise occult amelanotic ciliary body melanoma. The histopathological confirmation of retinal invasion, together with marked pathological discordance between sequential specimens, highlights the importance of clinicopathological correlation and the need to consider intratumoral heterogeneity in ciliary body melanoma.