Answer: Reaction to hip prosthesis

Histology: The sinuses of the lymph node are expanded by a population of cells with abundant lightly eosinophilic cytoplasm. The nuclei of these cells appear bland without prominent nucleoli. Within the cytoplasm of the cells there are small black particles some of which appear to be dust-like others appear to be larger. There is no evidence of emperipolesis. Nuclei appear round without nuclear grooves. Nuclei lack prominent nucleoli typical of malignant melanoma. Although at first appearance the black dust-like material could be interpreted as dirt on the slide, all of the material is centered over the cytoplasm of the histocytic cells and not present anywhere else on the slides.

Discussion: The typical scenario where one sees reaction to a hip prosthesis is in pelvic lymph nodes removed at the time of radical prostatectomy in the patient with a hip replacement. The foreign material represents migration of cobalt-chromium and titanium micro particles from the articular prosthesis which can give rise to lymphadenopathy with histiocytosis. In the pelvic lymph nodes, a major pitfall is not to diagnose especially on frozen section metastatic adenocarcinoma of the prostate. The current case is unusual in that it occurs within an inguinal lymph node which is not typically sampled in patients with hip prosthesis. However, because of the history of melanoma of the scrotum the inguinal lymph nodes were sampled revealing the same process which in this case could be misinterpreted as metastatic malignant melanoma. The foamy cells are reactive to various histiocytic markers and are negative for S-100 protein in contrast to malignant melanoma.

Reference(s):
– Am J Surg Pathol 18;83-90, 1994.