title: Preliminary embryological study of the radiological concept of retroperitoneal interfascial planes: what are the interfascial planes?
abstract: OBJECTIVE
  Recently, the radiological concept of retroperitoneal interfascial planes has been widely accepted to explain the extension of retroperitoneal pathologies. This study aimed to explore embryologically based corroborative evidence, which remains to be elucidated, for this concept.
  
  
  METHODS
  Using serial or semi-serial transverse sections from 29 human fetuses at the 5th-25th week of fetal age, we microscopically observed the development of the retroperitoneal fasciae and other structures in the retroperitoneal connective tissue. A hypothesis for the formation of the interfascial planes was generated from the developmental study and analysis of retroperitoneal fasciae in computed tomography images from 224 patients.
  
  
  RESULTS
  Whereas the loose connective tissue was uniformly distributed in the retroperitoneum by the 9th week, the primitive renal and transversalis fasciae appeared at the 10th-12th week, as previous research has noted. By the 23rd week, the renal fascia, transversalis fascia, and primitive adipose tissue of the flank pad emerged. In addition, the primitive lateroconal fascia, which runs parallel to and close to the posterior renal fascia, emerged between the renal fascia and the adipose tissue of the flank pad. Conversely, pre-existing loose connective tissue was sandwiched between the opposing fasciae and was compressed and narrowed by the developing organs and fatty tissues.
  
  
  CONCLUSIONS
  Through this developmental study, we provided the hypothesis that the compressed loose connective tissue and both opposed fasciae compose the interfascial planes. Analysis of the thickened retroperitoneal fasciae in computed tomography images supported this hypothesis. Further developmental or histological studies are required to verify our hypothesis.
authors.affiliation: Senshu Trauma and Critical Care Center, Rinku General Medical Center, 2-23 Rinku-Ourai-Kita, Izumisano, Osaka, 598-0048, Japan, ishikawa@sccmc.izumisano.osaka.jp.
authors.forename: Kazuo
authors.initials: K
authors.lastname: Ishikawa
authors.forename: Shota
authors.initials: S
authors.lastname: Nakao
authors.forename: Gen
authors.initials: G
authors.lastname: Murakami
authors.forename: Jose Francisco
authors.initials: JF
authors.lastname: Rodríguez-Vázquez
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Matsuoka
authors.forename: Makoto
authors.initials: M
authors.lastname: Nakamuro
authors.forename: Takeshi
authors.initials: T
authors.lastname: Shimazu
mesh_terms: D005205:Fascia / Q000000981:diagnostic imaging; D005333:Fetus; D007668:Kidney / Q000000981:diagnostic imaging*; D012187:Retroperitoneal Space / Q000000981:diagnostic imaging; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*