title: Unilocular retroperitoneal cyst of mesothelial origin presenting as a renal mass.
abstract: We report the first 2 cases, to our knowledge, of retroperitoneal cysts with features of mesothelial differentiation that clinically mimic renal masses. The first lesion occurred in a 71-year-old man who presented with flank pain. Ultrasound and magnetic resonance imaging studies showed a unilocular cystic structure arising from the upper pole of the left kidney. The second lesion was in a 44-year-old woman who presented with left flank pain. Imaging studies revealed an 8-cm hemorrhagic cyst at the lower pole of the left kidney. Histologic examination of the nephrectomy specimens in each case revealed a unilocular cyst with intracystic and pericystic hemorrhage. In each case, the cyst was lined by a single layer of cells with ample eosinophilic cytoplasm and benign nuclear features without mucinous or müllerian differentiation. Histochemical staining showed Alcian blue positivity on the cell surface, which was sensitive to hyaluronidase digestion. Intracytoplasmic mucin, however, was not detected. Immunostaining showed that the cyst lining cells were positive for keratin, vimentin, HBME-1, WT1, and thrombomodulin but negative for carcinoembryonic antigen, B72.3, Leu-M1, and BerEP4. The first case was positive for calretinin, whereas the second was negative. These findings support the mesothelial nature of the cysts.
authors.affiliation: Department of Pathology, Baylor College of Medicine, and The Methodist Hospital, Houston, Tex 77030, USA.
authors.forename: V C
authors.initials: VC
authors.lastname: Smith
authors.forename: R A
authors.initials: RA
authors.lastname: Edwards
authors.forename: J L
authors.initials: JL
authors.lastname: Jorgensen
authors.forename: R A
authors.initials: RA
authors.lastname: Goldfarb
authors.forename: D
authors.initials: D
authors.lastname: Kadmon
authors.forename: P
authors.initials: P
authors.lastname: Cagle
authors.forename: L D
authors.initials: LD
authors.lastname: Truong
mesh_terms: D000328:Adult; D000368:Aged; D000954:Antigens, Surface / Q000378:metabolism; D003560:Cysts / Q000378:metabolism / Q000473:pathology* / Q000601:surgery; D003937:Diagnosis, Differential; D005260:Female; D006470:Hemorrhage / Q000209:etiology; D006801:Humans; D007150:Immunohistochemistry; D007680:Kidney Neoplasms / Q000378:metabolism / Q000473:pathology / Q000601:surgery; D008297:Male; D018301:Neoplasms, Mesothelial / Q000378:metabolism / Q000473:pathology* / Q000601:surgery; D009392:Nephrectomy; D010146:Pain / Q000209:etiology; D012186:Retroperitoneal Neoplasms / Q000378:metabolism / Q000473:pathology* / Q000601:surgery
chemical_list: D000954:Antigens, Surface