Under the Skin: A Review of Sea Urchin Granulomas and Delayed Dermal Reactions to Echinoid Spines

Sea urchin injuries are common in coastal and tropical environments, often resulting in immediate pain and mechanical trauma. In a subset of patients, retained spine fragments trigger delayed granulomatous reactions that present diagnostic and therapeutic challenges. These "sea urchin granulomas" encompass a histopathologic spectrum including foreign body, sarcoidal, suppurative, and necrobiotic subtypes. This review synthesizes clinical, immunologic, diagnostic, and therapeutic insights from 36 peer-reviewed studies describing over 120 cases. Granulomas typically emerge weeks to months after injury, complicating recognition and frequently mimicking other dermatoses. Histologic evaluation often reveals sarcoidal and foreign body patterns, with immunohistochemistry highlighting T-cell-mediated responses. Diagnosis requires a combination of detailed exposure history, imaging (eg, ultrasound, magnetic resonance imaging), and biopsy to identify retained spines or rule out infectious or neoplastic mimics. Management strategies range from surgical excision and intralesional corticosteroids to novel approaches such as erbium-doped yttrium aluminum garnet laser ablation. Despite the morbidity associated with delayed or missed diagnosis, sea urchin granulomas remain underrecognized in dermatology practice. Increased awareness and standardized diagnostic workups are critical for improving outcomes. Dermatologists, particularly in coastal regions, should maintain a high index of suspicion for chronic nodular lesions arising after marine exposure.