Syringomyelia is present in 30 to 70% of CM-I patients.[1-3] The progression of syringomyelia associated with CM-I is due to the action of the cerebellar tonsils, which partially occlude the subarachnoid space at the
foramen magnum and act as a piston on the partially enclosed spinal subarachnoid space.[15] Syringomyelia can be also associated with specific clinical signs and symptoms.
e) Height of
foramen magnum (Hfm): The distance between the midpoints of the dorsal ventral rims of the
foramen magnum.
Foramen magnum dimensions are specific for a particular population and become low, when applied to populations with a large ethnic mix.
Evidence of concurrent caudal brain stem displacement was based on evidence that the cervicomedullary junction (using the obex as a landmark) approached or passed the
foramen magnum line.
Caption: Figure 1: MRI of the brain shows Chiari malformation type 1 with herniation of the cerebellar tonsils beneath the
foramen magnum of 17 mm and adenoid hypertrophy.
However, when you look at the full range of diversity across mammals, the evidence is compelling that bipedalism and a forward-shifted
foramen magnum go hand-in-hand."
The abrupt acceleration/deceleration injury that ensues in high energy blunt trauma strips the tectorial membrane from the occipital bone at the
foramen magnum and the posterior aspect of the C1 anterior arch.
(1) The
foramen magnum length (FML) direct distance from basion to opisthion
CSF leakage occurred in 7/50 (14%) cases of retrosigmoid sur-geries for Cerebellopontine (CP) Angle SOLs, 12/59 (20.3%) cases of midline suboccipital craniectomies for 4th ventricle/cerebellar SOLs, 4/12 (33.3%) cases of
foramen magnum SOLs, and 2/6 (33.3%) cases of chiari malformations.
It is a bony process in the median line located at the front rim of the occipital
foramen magnum. It is always present in reptiles.
The inverted L-shaped flap and muscles, which had been fully freed, were turned outward, and the external occipital protuberance, middle line, superior nuchal line, part of superior border of the
foramen magnum and mastoid process were completely exposed.
In most cases, the posterior fossa is small, and neural elements are crowded and impacted at the
foramen magnum.1 There was a time when lots of scholars acknowledging the crowding theory which postulated that restricted growth of the posterior fossa causes compression of neural tissue, which is then squeezed through the
foramen magnum like toothpaste through a tube.5 In support of this theory, the posterior fossa is abnormally small and the torcula is displaced downward in patients with Chiari malformations.6 This is a kind of naive materialism and simple and dialectical view on the pathological theory of Chiari malformation.
