Pediatric Solitary Epithelioid Histiocytoma of the Face.

Background: Solitary epithelioid histiocytoma, also known as reticulohistiocytoma, is a rare benign histiocytic proliferation with an unreported incidence that commonly presents as a superficial nodule involving the trunk and extremities of adults. Pathology shows dermal histiocytic infiltration composed of large, eosinophilic histiocytes with "glassy" cytoplasm and oncocytic macrophages. When presenting as part of a systemic disorder, it is called multicentric reticulohistiocytosis, a rare and more aggressive condition characterized by multiple skin and mucosal lesions and arthritis.

Clinical Case: A 5-year-old African American male patient presented to the pediatric plastic surgery clinic with a lesion of his lower lip 3 months after its initial appearance. Ultrasound identified a hypoechoic heterogenous nodule with increased vascularity. The lesion was excised in the operating room. Pathology revealed a highly cellular nodular proliferation of large epithelioid histiocytes with abundant glassy, lightly eosinophilic cytoplasm and mildly pleomorphic, generally eccentric, round-to-elongated nuclei. The large epithelioid cells were strongly and consistently positive for CD163 and CD68. The diagnosis was determined to be a benign histiocytic proliferation most consistent with solitary epithelioid histiocytoma. At 2-week and 2-month follow-up, the area was healing well and there was no evidence of recurrence.

Conclusion: This is an unusual presentation of a rare but benign histiocytic proliferation on the face of a young child. When pediatric patients are referred to a plastic surgery clinic for excisional biopsy of facial lesions, it is important to be aware of the broad range of differential diagnoses, including histiocytic proliferations, to treat the patient appropriately.