BACKGROUND: The causative role played by intra-abdominal pressure (IAP) in the syringogenesis of the Chiari 1 malformation syringomyelia has been still not adequately studied. The aim of this study is to validate the transmedullary theory about the hindbrain-related syrinx, also discussing the implications for safety of these patients related to the use of high-pressure CO2 pneumoperitoneum during laparoscopic and robotic surgery. METHODS: Fourteen patients with a hindbrain-related syrinx were candidate for a posterior fossa decompression. Preoperative and follow-up protocol involved conventional T1/T2 and cardiac-gated Cine phase-contrast MRI sequences. Peak systolic and diastolic velocities were acquired at four Regions Of Interests (ROI), namely syrinx, ventral and dorsal cervical subarachnoid space, and foramen magnum region. Data were reported as mean ± SD. Patients were followed for three years. One-way ANOVA with Bonferroni post hoc test of multiple comparisons were performed, where p-value was <0.001. RESULTS: A systolic-diastolic pulsatile pattern of CSF was found in all cases inside the syrinx. Syrinx and premedullary cistern velocities decreased within the first month after surgery (<0.001). All symptoms apart from atrophy and spasticity improved. These data lead to validate the Oldfield and Heiss transmedullary theory about syringogenesis, within which an increased IAP play a key role. CONCLUSION: Raised IAP plays a paramount role in the formation and maintenance of the hindbrain-related syrinx. High-pressure CO2 surgical pneumoperitoneum is strongly discouraged in these patients because at risk of rapid neurological worsening. A low-pressure insufflation technique has a rationale in those patients having smaller or incidental syrinxes.