Uric Acid Crystal Deposition Within a Ganglion Cyst: A Case Report.

Ganglion cysts are soft tissue swellings occurring most commonly in the hand or wrist. They are typically filled with gelatinous material rich in hyaluronic acid and mucopolysaccharides. Although benign, variations in cyst content can provide important insight into underlying metabolic or microenvironmental processes. To date, uric acid crystal deposition within a ganglion cyst has not been reported. This case describes a 73-year-old woman with a history of breast cancer, treated with exemestane, who presented with a painful mass on the dorsum of the left midfoot. Physical examination revealed a fluctuant, soft tissue lesion without overlying erythema. Aspiration yielded yellow-tinged gelatinous fluid, which on histopathologic examination was consistent with a ganglion cyst. Under polarized light, needle-shaped crystals suggestive of monosodium urate were identified. The patient's serum uric acid was at the upper limit of normal, and she reported arthralgias associated with exemestane therapy, but she had no clinical history of gout. This case represents an unusual presentation of a ganglion cyst containing uric acid crystals in the absence of gout or significant hyperuricemia. We propose that the mucopolysaccharide-rich microenvironment of the cyst may promote crystal precipitation independent of systemic metabolic disease. Exemestane-related tissue changes may also play a role, though further investigation is warranted. Recognition of this finding underscores the value of histopathologic evaluation in atypical cyst presentations and suggests potential links between local biochemical environments and crystal formation that merit future study.