title: Undifferentiated pleomorphic sarcoma of the liver presenting as a unilocular cyst.
abstract: BACKGROUND
  A malignant fibrous histiocytoma, recently referred to as an undifferentiated pleomorphic sarcoma (UPS), is very rare in the liver, and only 34 cases of primary hepatic malignant fibrous histiocytoma have been reported in the English literature.
  
  
  METHODS
  We report a rare case of a hepatic UPS presenting as a unilocular cystic lesion with respect to histopathologic features, the newly revised diagnostic criteria, and the differential diagnosis.
  
  
  RESULTS
  A 60-year-old man presented for evaluation of epigastric pain of 7 months duration. Abdominal computed tomography revealed a hypodense, unilocular cystic mass in the right lobe of the liver, measuring 14.0X11.1 cm. A right lobectomy was performed. Grossly, the cut surface showed a single, well-circumscribed unilocular cystic tumor mass containing dark red-brown necrotic debris and blood clots, which occupied most of the mass. Microscopically, the tumor consisted of haphazardly arranged mononuclear pleomorphic tumor cells, admixed with abundant osteoclast-like multinucleated giant cells. Immunohistochemically, the tumor cells expressed vimentin only. The histopathologic and immunohistochemical findings were compatible with a UPS. The patient is alive and well 41 months after surgery without recurrence.
  
  
  CONCLUSIONS
  Clinically, most of the hepatic UPSs are solid masses. Only two cases have presented as multilocular cystic masses. A primary hepatic UPS presenting as a unilocular cyst has never been reported. A UPS should be included in the differential diagnosis of unilocular cystic lesions in the liver.
authors.affiliation: Department of Pathology, School of Medicine, Kyung Hee University, 1 Hoegi-dong, Dongdaemun-gu, 130-702 Seoul, South Korea.
authors.forename: Hyun-Soo
authors.initials: HS
authors.lastname: Kim
authors.forename: Gou Young
authors.initials: GY
authors.lastname: Kim
authors.forename: Sung-Jig
authors.initials: SJ
authors.lastname: Lim
authors.forename: Sang Mok
authors.initials: SM
authors.lastname: Lee
authors.forename: Youn Wha
authors.initials: YW
authors.lastname: Kim
mesh_terms: D003560:Cysts / Q000175:diagnosis* / Q000473:pathology; D003937:Diagnosis, Differential; D051677:Histiocytoma, Malignant Fibrous / Q000175:diagnosis* / Q000473:pathology / Q000601:surgery; D006801:Humans; D008099:Liver / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D008107:Liver Diseases / Q000175:diagnosis* / Q000473:pathology; D008113:Liver Neoplasms / Q000175:diagnosis* / Q000473:pathology / Q000601:surgery; D008297:Male; D008875:Middle Aged; D012509:Sarcoma / Q000175:diagnosis* / Q000473:pathology / Q000601:surgery; D014057:Tomography, X-Ray Computed