Answer: Sloughed rete testis cells

Histology: In addition to the hydrocele sac, there are small detached clusters of “blue cells.” These clusters are composed of cells with a high nuclear cytoplasmic ratio, slight spindling of the nuclei and are associated with spermatozoa in the adjacent tissue. The nuclei are relatively bland with no mitotic figures or apoptotic bodies. A submitted stain for CD56 was positive.

Discussion: We have reported on cases of hydrocele and spermatocele resections containing detached small cellular “blue” clusters, raising questions of small cell carcinoma by contributors to our consult service. On routine stained sections, there were multiple clusters of detached hypercellular cells with focal streaming, high nuclear-to-cytoplasmic ratios, and hyperchromatic nuclei without prominent nuclei. There were no mitotic figures, apoptotic bodies, or necrosis. CD56 was typically positive, yet synaptophysin and chromogranin were negative in all cases of “blue cells.” The immunohistochemistry pattern was similar to that seen in normal rete testis. Ki-67 was negative or showed only rare positive cells in all of the cases of the “blue cells.” Clusters of blue cells suggestive of sloughed rete testis cells can mimic small cell carcinoma in hydrocele and spermatocele specimens based on their low power appearance and positive CD56 staining. Closer examination of the cells’ bland morphology, low expression of Ki-67, and lack of chromogranin and synaptophysin, along with recognition of this entity, can prevent a misdiagnosis of malignancy.

Reference(s):
– Human Pathology 2010; 41:88-93.