case_images: PMC6540500_01
case_images: Magnetic resonance imaging (MRI) of metastatic spindle cell squamous cell
  carcinomas involvement of the brainstem prior to pembrolizumab. Sagittal and
  axial T1 weighted post-contrast fat-saturated images, performed on Siemens
  MRI scanner, show intracranial extension of the mass lesion through
  perineural spread. There is involvement of the right trigeminal nerve along
  its course through the foramen ovale and Meckel's cave, which extends
  posteriorly to involve the anterior surface of pons and medulla on the right
  side. The axial image also demonstrates the spread along the right abducens
  nerve along the Dorello's canal with its cisternal portion extending
  posteriorly to involve the anterior pontomedullary junction. Enhancing mass
  lesion is seen along the clivus on the right side as well.
case_images: 10.1177_2324709619850216-fig1.jpg
case_images: PMC6540500_01_10.1177_2324709619850216-fig1.jpg
case_images: fig1-2324709619850216
case_images: An MRI showed interval increase in the enhancement of the V3 portion of the right trigeminal nerve extending into the foramen ovale and destruction of the clivus on the right side with involvement of the right sixth CN (Figure 1).
case_images: Magnetic resonance imaging of the brainstem following 15 months of
  pembrolizumab treatment. Comparable axial and sagittal post-contrast
  fat-saturated images to Figure 1 following treatment demonstrate significant interval
  improvement with near complete resolution of enhancement along the anterior
  surface of brainstem. The degree of involvement of the right trigeminal and
  abducens nerve in the region of Meckel's cave and Dorello's canal also shows
  significant interval improvement.
case_images: 10.1177_2324709619850216-fig2.jpg
case_images: PMC6540500_01_10.1177_2324709619850216-fig2.jpg
case_images: fig2-2324709619850216
case_images: Repeat MRI as of November 2018 has demonstrated continued response with near complete resolution in enhancement along the pontomedullary junction in the region of CN VI, with stable disease at the right clivus, and with no new areas of enhancement (Figure 2).