. The diseases of infancy and childhood. his prevents the union of the parts of the vertebralarches. Although the tumor is generally associated with a bifid spine, thisis not necessarily the case. The protrusion may take place through theintervertebral notch or foramen, or there may be a fissure of the bodiesof the vertebrae, and an anterior tumor projecting into the cavity of thethorax, abdomen, or pelvis; the tumor may be so small as not to be recog-nized externally—spina bifida occulta. The principal anatomical varie-ties are meningocele, meningomyelocele, and syringomyelocele. Meningocele.
. The diseases of infancy and childhood. his prevents the union of the parts of the vertebralarches. Although the tumor is generally associated with a bifid spine, thisis not necessarily the case. The protrusion may take place through theintervertebral notch or foramen, or there may be a fissure of the bodiesof the vertebrae, and an anterior tumor projecting into the cavity of thethorax, abdomen, or pelvis; the tumor may be so small as not to be recog-nized externally—spina bifida occulta. The principal anatomical varie-ties are meningocele, meningomyelocele, and syringomyelocele. Meningocele.—In this form there is a protrusion of the membranesonly (Fig. 121). The accumulation of fluid is either in the arachnoidcavity or the subarachnoid space posterior to the cord. The opening ofcommunication between the tumor and the spinal canal is small in thisvariety, usually being about one-twelfth to one-sixth of an inch in diam-eter. There may, however, be no communication. The skin is usually27 798 DISEASES OF 1HE NERVOUS SYSTEM. fully developed (Fig. 122). The tumor is frequently globular, some-times pedunculated, and may attain a very large size, being as much as five or six inches in diameter. Thisis because spontaneous rupture isnot likely to occur, and the tumordoes not become infected except by/ ^k jf operative interference. With such tumors patients may live to adultlife. This variety is most frequent-^^^ ly seen in the cervical region. It has the best chance of natural recover},and in it operation gives the best re-sults. Meningomyelocele.—This is byfar the most frequent variety ofspina bifida. It is the form usuallyseen in the sacrolumbar accumulation of fluid takesplace in the anterior subarachnoidspace, less frequently in the anteriorarachnoid cavity (Fig. 123). Inthis form the cord is contained inthe sac, and usually forms a part ofits wall. The tumor is smaller than the meningocele, the usual size beingthat of a mandarin orange. It is sessile,
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