 Again seen are postsurgical changes of Chiari decompression including suboccipital craniectomy and resection of the posterior arch of C1. Again seen are foci of deformity of the posteroinferior aspect of the cerebellum, with tenting towards the overlying dura and unchanged. There is a retroflexed dens with associated narrowing of the column of cerebrospinal fluid flow across the anterior neo-foramen magnum. Biphasic flow anteriorly at the foramen magnum is otherwise preserved. There is diminished CSF flow and diminished CSF space dorsal to the cervical cord, not significantly changed since 2/11/2016, allowing for slight differences in technique. Biphasic flow at the foramen Magendie appears preserved.There appears to be slight further decrease in size of the thoracic syrinx with minimal residual prominence of the central canal measuring 1 to 2 mm seen at T5-T6 and in the mid to lower thoracic cord more inferiorly. Previous seen tiny syrinx which is less visible on the current study is likely partly related to motion degradation on the current study. No new cord signal abnormality. Vertebral body heights and alignment are grossly unremarkable aside from mild straightening. Conus is in normal position at the upper L2 level. No spinal canal or neural foraminal stenosis is evident.
Postoperative findings related to Chiari decompression again seen. Compared to 2/11/2016, there is no significant change in the appearance of the posterior fossa including retroflexed dens with associated narrowing of the anterior column of CSF flow as well as tenting of cerebellar tissue towards the overlying dura posteriorly, which may represent an adhesion. Motion degradation limits comparison, however, the residual tiny mid thoracic syrinx seen previously on 2/11/2016 is stable to slightly further decreased. Syrinx is markedly decreased when compared to 10/22/2015.