The mendosal suture joins the interparietal and inferior portions of the occipital bone. Persistent patency of this suture can result in bathrocephaly, an abnormal occipital projection. This study aims to determine normal temporal fusion of the mendosal suture and cranial shape of the patients with persistent suture patency. A retrospective review of head CT scans in patients aged 0-18 months who presented to the emergency department between 2010 and 2020 was completed. Presence and patency of the mendosal suture were assessed. Cranial shape analysis was conducted in the cases that presented with 100% suture patency and age-matched controls. An exponential regression model was used to forecast the timing of suture fusion. In total, 378 patients met inclusion criteria. Median age at imaging was 6.8 months (IQR 2.9, 11.6). Initiation of mendosal suture fusion was observed as early as 4 days of age and was completed in all instances except one by age 18 months. Most patients had either a complete or partial suture fusion (66.7% versus 30.7%, respectively), and 2.6% of patients had 100% suture patency. Cranial shape analysis demonstrated increased occipital projection in patients with 100% suture patency compared with their controls. Exponential regression model suggested that the mendosal suture closure begins prenatally and typically progresses to full closure at the age of 6 months. Prevalence of a patent mendosal suture was 2.6% overall. Mendosal suture fusion initiates in-utero and completes ex-utero within the first 18 months of life. Delayed closure results in greater occipital projection.