title: Anal sphincter complex: 2D and 3D endoanal and translabial ultrasound measurement variation in normal postpartum measurements.
abstract: OBJECTIVE
  Women may experience anal sphincter anatomy changes after vaginal birth (VB) or Cesarean delivery (CD). Therefore, accurate and acceptable imaging options to evaluate the anal sphincter complex (ASC) are needed. ASC measurements may differ between translabial (TLUS) and endoanal (EAUS) ultrasound imaging and between 2D and 3D US. The objective of this analysis was to describe measurement variation between these modalities.
  
  
  METHODS
  Primiparous women underwent 2D and 3D TLUS imaging of the ASC 6 months after VB or CD. A subset of women also underwent EAUS measurements. Measurements included internal anal sphincter (IAS) thickness at proximal, mid, and distal levels and the external anal sphincter (EAS) at 3, 6, 9, and 12 o'clock positions, as well as bilateral thickness of the pubovisceralis muscle (PVM).
  
  
  RESULTS
  There were 433 women presenting for US: 423 had TLUS and 64 had both TLUS and EAUS of the ASC. All IAS measurements were significantly thicker on TLUS than EAUS (all p < 0.01), while EAS measurements were significantly thicker on EAUS (p < 0.01). PVM measurements with 3D or 2D imaging were similar (p > 0.20). On both TLUS and EAUS, there were multiple sites where significant asymmetry existed in left versus right measurements.
  
  
  CONCLUSIONS
  US modality used to image the ASC introduces small but significant changes in measurements, and the direction of the bias depends on the muscle and location being imaged.
authors.affiliation: Department of Obstetrics and Gynecology, University of New Mexico Health Sciences Center, Albuquerque, NM, USA, meriwet2@salud.unm.edu.
authors.forename: Kate V
authors.initials: KV
authors.lastname: Meriwether
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Hall
authors.forename: Lawrence M
authors.initials: LM
authors.lastname: Leeman
authors.forename: Laura
authors.initials: L
authors.lastname: Migliaccio
authors.forename: Clifford
authors.initials: C
authors.lastname: Qualls
authors.forename: Rebecca G
authors.initials: RG
authors.lastname: Rogers
mesh_terms: D000328:Adult; D001003:Anal Canal / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D002585:Cesarean Section; D019160:Endosonography; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D049590:Postpartum Period; D014463:Ultrasonography / Q000379:methods; D055815:Young Adult