Bilateral extensive adult-onset limbal xanthogranuloma invading the deep corneal stroma: a case report and literature review.

Background: Adult-onset xanthogranuloma (AOXG) is a rare, benign form of non-Langerhans cell histiocytosis. Ocular manifestations commonly involve the orbit, uveal tract, or adnexal tissues; however, concurrent bilateral involvement accompanied by extensive infiltration of the corneoscleral limbus remains exceptionally rare and poses substantial diagnostic and therapeutic challenges. Case presentation: A 48-years-old male presented with a 20-years history of progressively enlarging bilateral, yellow-white corneoscleral lesions associated with severe visual impairment (right eye best-corrected visual acuity: 0.02). The patient subsequently underwent right eye corneal lesion excision combined with lamellar keratoplasty (LKP). Histopathological and immunohistochemical evaluation demonstrated a dense subepithelial infiltration of lipid-laden histiocytes and characteristic Touton giant cells, with immunoreactivity for CD68 and negative staining for S-100 and CD1a. Owing to the highly unusual bilateral presentation, a thorough systemic evaluation was initiated to exclude potentially lethal systemic histiocytoses, particularly Erdheim-Chester disease (ECD). Whole-body imaging revealed no evidence of visceral involvement or osteosclerotic lesions. Furthermore, molecular analysis confirmed a wild-type BRAF gene, while serum immunoelectrophoresis demonstrated no evidence of monoclonal gammopathy. Based on these comprehensive findings, a definitive diagnosis of AOXG was established. Following treatment, the patient demonstrated excellent anatomical resolution without evidence of recurrence and accompanied by a modest visual improvement to a BCVA of 0.1 throughout the 18-months follow-up period. Conclusion: Bilateral extensive limbal AOXG is a rare entity that can easily be misdiagnosed as corneal degeneration, squamous cell carcinoma, or sclerocornea. Persistent chronic inflammation alongside hyperlipidemia may have contributed to the disease's etiology. Regarding lesions exhibiting deep stromal invasion, integrating LKP with intralesional corticosteroid administration may be a useful therapeutic approach in selected vision-threatening cases.