title: Surgical anatomy of the superior orbit on ultra-high-resolution MRI at 9.4 Tesla.
abstract: BACKGROUND
  A good understanding of the anatomical details is required to ensure optimal results during surgery of the orbit. Several indications for orbital surgery require biopsy, resection, or reconstructive procedures. The intricate relationships between the orbital septum and adjacent structures of the upper orbit can cause difficulties in interpreting the surgical anatomy of this region. The purpose of this study was to acquire further insight into the anatomy of the superior part of the orbit, with special attention paid to the orbital septum.
  
  
  METHODS
  An ex-vivo study was performed using magnetic resonance imaging (MRI) at 9.4 Tesla (isotropic resolution = 20 μm) on six human cadaver specimens to examine the superior-medial half of the orbit. To visualise the posterior layers of the upper orbit, a dissection of three of the orbits was performed prior to the MRI examination, and a flexible PVC sheet was introduced above the levator muscle.
  
  
  RESULTS
  The technique enabled a visualisation of anatomically important landmarks of the anterior and posterior parts of the upper orbit at a resolution near histological levels; to the authors' knowledge, this visualisation has not been reported previously. A posterior continuation of the orbital septum, which forms a distinct anatomical structure, is revealed.
  
  
  CONCLUSIONS
  The posterior aspect of the orbital septum separates the levator muscle and the orbital fat pad. Between these two structures, a surgical corridor is formed using MRI, enabling alternative access to the superior part of the orbit; this alternative access might be less invasive because the orbital septum remains undamaged.
authors.affiliation: a 1 Department of Ophthalmology, Oslo University Hospital and Norwegian Centre for Eye Research.
authors.forename: Dag
authors.initials: D
authors.lastname: Krohn-Hansen
authors.affiliation: b 2 Institute for Experimental Medical Research, Oslo University Hospital , Oslo, Norway.|c 3 University of Oslo , Oslo, Norway.
authors.forename: Lili
authors.initials: L
authors.lastname: Zhang
authors.affiliation: a 1 Department of Ophthalmology, Oslo University Hospital and Norwegian Centre for Eye Research.
authors.forename: Erling
authors.initials: E
authors.lastname: Haaskjold
authors.affiliation: d 4 Department of Neurosurgery, Oslo University Hospital , Oslo, Norway.
authors.forename: Torstein R
authors.initials: TR
authors.lastname: Meling
authors.affiliation: a 1 Department of Ophthalmology, Oslo University Hospital and Norwegian Centre for Eye Research.|c 3 University of Oslo , Oslo, Norway.
authors.forename: Bjørn
authors.initials: B
authors.lastname: Nicolaissen
authors.affiliation: b 2 Institute for Experimental Medical Research, Oslo University Hospital , Oslo, Norway.|c 3 University of Oslo , Oslo, Norway.
authors.forename: Ivar
authors.initials: I
authors.lastname: Sjaastad
keywords: Ultra-high-resolution MRI; orbit; orbital anatomy; orbital septum; orbital surgery