The mendosal suture (also known as the accessory occipital suture) is a normal calvarial suture.
The suture extends through the occipital bone, lying superior to the occipitomastoid suture and inferiomedial to the lambdoid suture. It closes in utero or in the first few days of life. It is usually seen bilaterally but can be unilateral.
This suture can occasionally persist into childhood, however the vast majority close before 6 years of age. One study of 500 dried skulls from adults and children in an indian subcontinent population demonstrated a mendosal suture in 3% of skulls1.