The foramen magnum is a bony opening in the region of the posterior cranial fossa, through which the Medulla oblongata passes and thereby connects with the spinal cord.
Anatomy
The foramen magnum is located in the Os occipitale. In addition to the medulla oblongata, the following structures pass through the foramen magnum:
Spinal root of the Nervus accessorius
The left and right Vertebral artery
The right and left Arteria spinalis posterior
Spinal vein
The foramen magnum marks the transition of the cranial dura mater into the spinal dura mater.
Osteometric measurements
The foramen magnum has the following sagittal and transverse osteometric measurements[^1]:
Dimensions of the foramen magnum | Mean | Minimum - Maximum |
Sagittal diameter | 36,6 mm | 30,1 - 42,6 mm |
Transverse diameter | 31,1 mm | 25,0 - 38,9 mm |
Imaging
Clinical relevance
Herniation
If intracranial pressure is too high, parts of the brain may be displaced downward into the foramen magnum, resulting in herniation.
Foramen Magnum Stenosis
In patients with skeletal dysplasia, such as achondroplasia, stenosis of the foramen magnum may occur[^2].