Purpose To explore the clinicopathologic features,pathogenesis and differential diagnosis of Malaco-plakia.Methods The clinical features,imaging manifestations,cytopathologic features,histopathologic features,im-munohistochemistry,special staining and molecular pathological manifestations of 17 patients with Malacoplakia were analysed and the relevant literature was reviewed.Results Seventeen patients with Malacoplakia were mostly female,of which 13 lesions were located in the bladder,1 in the prostate,1 in the colon,1 in the right external auditory canal,and 1 in the retroperitoneum.Cytologic morphology varied depending on the site of the lesion,with phagocytes and MG-like microsomal analogues seen in renal puncture cytology,and small numbers of squamous epithelial cells and uroepi-thelial cells(NHGUC)seen in urinary cytology specimens.Histologic morphology showed a large number of foamy his-tiocytes and small numbers of neutrophils and eosinophils against a background of chronic inflammation dominated by lymphocytes and plasma cells;the cytoplasm of the histiocytes was eosinophilic and granular,with blue calcified vesi-cles scattered throughout,some of which were in the form of target-ring or concentric-circle-like structures,which are known as Michaelis-Gutmann bodies(MG bodies).Special stains showed PAS and iron staining(+);immunohisto-chemistry showed diffuse histiocyte CD68(+),CD163(+),CK(AE1/AE3)(-);molecular pathology showed TB-DNA(-).Conclusion Malacoplakia is a chronic granulomatous disease that can be cured.Imaging often shows occupancy,which is easily misdiagnosed as a tumour clinically,and confirming the diagnosis mainly relies on patholog-ical diagnosis,differential diagnosis includes xanthogranulomatous cystitis,xanthogranulomatous pyelonephritis,colon cancer,granulosa cell tumour and Langerhans histiocytosis.

Purpose To explore the clinicopathologic features,pathogenesis and differential diagnosis of Malaco-plakia.Methods The clinical features,imaging manifestations,cytopathologic features,histopathologic features,im-munohistochemistry,special staining and molecular pathological manifestations of 17 patients with Malacoplakia were analysed and the relevant literature was reviewed.Results Seventeen patients with Malacoplakia were mostly female,of which 13 lesions were located in the bladder,1 in the prostate,1 in the colon,1 in the right external auditory canal,and 1 in the retroperitoneum.Cytologic morphology varied depending on the site of the lesion,with phagocytes and MG-like microsomal analogues seen in renal puncture cytology,and small numbers of squamous epithelial cells and uroepi-thelial cells(NHGUC)seen in urinary cytology specimens.Histologic morphology showed a large number of foamy his-tiocytes and small numbers of neutrophils and eosinophils against a background of chronic inflammation dominated by lymphocytes and plasma cells;the cytoplasm of the histiocytes was eosinophilic and granular,with blue calcified vesi-cles scattered throughout,some of which were in the form of target-ring or concentric-circle-like structures,which are known as Michaelis-Gutmann bodies(MG bodies).Special stains showed PAS and iron staining(+);immunohisto-chemistry showed diffuse histiocyte CD68(+),CD163(+),CK(AE1/AE3)(-);molecular pathology showed TB-DNA(-).Conclusion Malacoplakia is a chronic granulomatous disease that can be cured.Imaging often shows occupancy,which is easily misdiagnosed as a tumour clinically,and confirming the diagnosis mainly relies on patholog-ical diagnosis,differential diagnosis includes xanthogranulomatous cystitis,xanthogranulomatous pyelonephritis,colon cancer,granulosa cell tumour and Langerhans histiocytosis.