title: Horizontal liver cleft: a rare anatomic variant.
abstract: BACKGROUND
  Improvements in hepatobiliary surgical techniques, with increased usage of segmental and subsegmental resection, make accurate preoperative radiological assessment delineation of the liver segments ever more crucial. Conventionally, this is done by drawing imaginary straight planes along the portal and hepatic veins. We herein report a rare case of a horizontal cleft between the superior and inferior liver segments seen on CT.
  
  
  METHODS
  A 74-year-old female patient with a known medical history of ovarian cancer with peritoneal metastasis and retroperitoneal lymphadenopathy was referred to our department for CT to assess disease response after treatment. On contrast-enhanced CT, apart from the ovarian cancer, the liver had a smooth, well-defined horizontally orientated cleft that broadly divided the organ into 2 halves. The cleft contained the right and left main portal veins, and consequently had a curved down-sloping configuration accommodating the curved course of these veins. This liver cleft was present from an earlier CT study performed 3 years ago, and there was no history of preceding liver surgery.
  
  
  CONCLUSIONS
  To the best of our knowledge, this is the first report of the anomaly of a horizontal liver cleft, which may be attributed to early cessation of the embryological formation of the liver. This liver cleft also illustrates the difficulties in liver segmentation using Couinaud's classification.
authors.affiliation: Department of Diagnostic Radiology, Tan Tock Seng Hospital, Singapore, Singapore.
authors.forename: Yong Han
authors.initials: YH
authors.lastname: Ting
authors.affiliation: Department of Diagnostic Radiology, Tan Tock Seng Hospital, Singapore, Singapore.
authors.forename: Kian Soon
authors.initials: KS
authors.lastname: Lim
mesh_terms: D000368:Aged; D003937:Diagnosis, Differential; D005260:Female; D006503:Hepatic Veins / Q000000981:diagnostic imaging*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008099:Liver / Q000002:abnormalities* / Q000098:blood supply; D008107:Liver Diseases / Q000151:congenital* / Q000000981:diagnostic imaging; D010690:Phlebography; D011169:Portal Vein / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed