The Role of Fine‐Needle Aspiration in Conjunction With Ancillary Immunophenotyping for Accurate Recognition of a Case of Splenosis in Perirectal Soft Tissue

Splenosis is the implantation of splenic tissue into other organs following splenectomy or traumatic spleen injury. It typically manifests in the peritoneal cavity but can appear in other locations. Splenic nodules are often incidentally discovered during imaging, with nuclear scintigraphy being the gold standard for recognition. We report a case of splenosis found incidentally upon computed tomography for evaluation of chronic anemia in the anterior perirectal space of a 74-year-old man who had previously undergone splenectomy. Despite advances in imaging techniques, tissue examination is necessary to confirm suspected splenosis and exclude neoplastic processes, and image-guided fine-needle aspiration biopsy is a valuable tool to this end. Our case was diagnosed by endoscopic ultrasound-guided fine-needle aspiration biopsy with ancillary immunohistochemistry and flow cytometry. Cytomorphological features alone may not be sufficient to recognize splenosis; ancillary immunostaining can highlight littoral cells lining the red pulp sinuses, with characteristic positive expression of CD8, WT1, ERG, and CD68, helping clinch the diagnosis.