The Cervical Subarachnoid Space, with Particular Reference to Syringomyelia and the Arnold-Chiari Deformity

Abstract

It is the object of this paper to call further attention to the subarachnoid space in the cervical spine. We believe that insufficient attention has been paid to this area in the past and that helpful information may be obtained by its study. A review of the literature suggests that less than 20 per cent of spinal cord tumors show evidence of their presence on films made without contrast media. We are aware of the fact that 80 to 85 per cent of such tumors may be diagnosed by myelographic studies employing opaque media, but we believe that an appreciable number may be demonstrated without subjecting the patient to that procedure. The contrast afforded by air or oxygen is very much less than that provided by lipiodol or pantopaque, but with careful technic it may nevertheless be adequate and possible complications which may arise from residues of oil in the basal cisterns or elsewhere in the spinal canal may thus be avoided. The subarachnoid space which surrounds the cervical cord is of sufficient volume to permit the collection of an appreciable amount of air or oxygen around the cord after withdrawal of the cerebrospinal fluid by means of lumbar puncture. This sleeve-like collection of gas is shown on lateral or oblique films as a line of diminished density lying anterior and posterior to the cord. The column of gas thus serves to delineate the spinal cord and to indicate not only its position within the canal but also its size. We have not been able to demonstrate it on anteroposterior films because of the density of the vertebral bodies. The normal spinal cord passes through the foramen magnum somewhat anterior to the center of the foramen, but is then directed slightly posteriorly, so that below the level of the second cervical vertebra it occupies an approximately symmetrical position within the canal. In the adult, the cord has a fairly constant diameter of about 1 cm. at the level of the atlas and axis. Below this there is a gradual increase in size to accommodate the cell bodies for the large number of nerves which go to the upper extremities. The enlargement is almost entirely in the transverse diameter of the cord, and (in the neck) is greatest at the level of the fifth and sixth cervical vertebrae. On films taken as indicated below, the diameter of the normal cord at this level averages 12 to 13 mm. It must be remembered that the spinal subarachnoid space is in direct communication with the subarachnoid spaces and ventricular system within the cranial cavity. In the normal subject this communication is of greatest caliber posterior to the cord as it passes through the foramen magnum. The portion of the spinal subarachnoid space which lies posterior to the cord is thus a direct extension downward of the cisterna magna; it is unfortunate that this cistern is frequently defined as having its inferior border at the level of the foramen.