Answer: Malakoplakia

Histology: The needle core normal architecture is totally effaced. Some areas show nonspecific fibrosis with lymphocytes and plasma cells. Other areas show cells with rounded bland nuclei and abundant eosinophilic cytoplasm admixed with both chronic inflammation and scattered neutrophils. Within the cells with abundant cytoplasm are small bluish round structures, some of which have a targetoid appearance.

Discussion: Malakoplakia may affect multiple organs including the prostate, although the bladder is most commonly involved. The lesion is characterized by large histiocytes, known as von Hansemann cells, and small basophilic extracytoplasmic or intracytoplasmic calculopherules, called Michaelis-Gutmann bodies. Bacteria or bacterial fragments form a nidus for the calcium phosphate crystals that laminate the Michaelis-Gutmann bodies. A defect in intraphagosomal digestion, which accounts for the unusual immune response, gives rise to malakoplakia. Patients may be debilitated, immunosuppressed, or have other chronic diseases. Management of malakoplakia is primarily based on controlling the urinary tract infections, which stabilizes the disease. Adding bethanechol, a cholinergic agent thought to increase intracellular cyclic guanosine monophosphate levels considered to be the defect causing macrophage dysfunction, may also be useful. Surgery may be necessary as the disease progresses, despite antimicrobial treatment. Iron and calcium stains can highlight Michaelis-Gutmann bodies, although they are usually quite evident on routine hematoxylin and eosin stained sections. Malakoplakia may clinically mimic prostate cancer, resulting in prostatic induration and a hypoechoic lesion seen on transrectal ultrasound. In rare cases with limited sampling, the large epithelioid histiocytes of malakoplakia may histologically mimic high grade prostatic adenocarcinoma. In addition to the unique findings of Michaelis-Gutmann bodies in malakoplakia, adenocarcinoma of the prostate rarely has admixed inflammatory cells. If one is considering diagnosing Gleason score 5+5=10 with inflammation, one should consider performing keratin and CD68 stains to differentiation between epithelial and histiocytic cells.