Posterior fossa protocol (MRI)

MRI protocol for assessing the posterior fossa, including the cerebellopontine angle, is a group of basic MRI sequences put together to best approach lesions involving the brainstem, cranial nerves (CN III to CN XII), cerebellum and CSF spaces (fourth ventricle, cisterna magna, prepontine cistern, and CPA cisterns).

NB: This article is intended to outline some general principles of protocol design. The specifics will vary depending on MRI hardware and software, radiologist's and referrer's preference, institutional protocols, patient factors (e.g. allergy) and time constraints.

Sequences

A good protocol for this purpose involves at least:

• T1
  • sequence: whole brain axial and sagittal, a volumetric acquisition is preferred when available
  • purpose:
• T2
  • sequence: axial with ultra thin slices (e.g. DRIVE, RESTOREm FRFSE)
    • T2* with ultra thin slices (e.g. 3D CISS, FIESTA, FFE)
  • purpose: useful to assess the CSF spaces and thus the cranial nerves, the Meckel's caves, the internal auditory canals and the fluid within the inner ear structures
• FLAIR
  • sequence: axial whole brain
• DWI/ADC
  • sequence: axial whole brain
• T1 C+ (Gd)
  • sequence: axial and coronal, a volumetric acquisition is preferred when available
  • T1 C+ (Gd) fat sat considered in at least one plane
  • gadolinium-based contrast agents (GBCAs) for CNS :
    • gadoterate meglumine (Dotarem®)
    • gadobutrol (Gadavist®)
    • gadopentetate dimeglumine (Magnevist®)
    • gadobenate dimeglumine (MultiHance®)
    • gadodiamide (Omniscan®)
    • gadoversetamide (OptiMARK®)
    • gadoteridol (ProHance®)
  • all these GBCAs are approved by FDA at identical administered total doses of 0.1mmol/kg body weight