In the section on General Malformations, this con-dition has already been considered. Rhachischisis, or spina bifida without tumour, has been sufficiently described (see p. 50), but the form associated with tumour requires fuller consideration.

The term spina bifida is by some limited to the tumescent form, which is therefore distinguished from rhachischisis, but this distinction cannot be fully carried out.

Spina Bifida With Tumour

The tumour forms a rounded swelling, which is usually situated in the lumbo-sacral region, but may be in any part of the column. There is usually a defect in the arches of the Vertebrae, and the swelling protrudes posteriorly; but there are a few lasts in which the bodies of the vertebrae are defective, and the swelling protrudes into the thorax, abdomen, or pelvis. 'There is sometimes no defect, or a very slight one, of the arches of the vertebrae, the protrusion passing between two adjacent arches.

The protrusion (Fig. 343) is covered with skin over the greater part of its surface, but in the central part there is often an area of membrane which contains none of the special structures of the skin, such as hairs and sebaceous glands. Inside the skin there are the membranes of the cord; but, according to Recklinghausen, the. dura mater is frequently defective to a similar extent with the skin, so that the sac is formed of pia-arachnoid, which is usually considerably thickened. There is generally a dimpling or umbilication at the summit of the tumour (see g in figure), and this sometimes amounts to a small canal which may directly communicate with the central canal of the cord. The umbilication corresponds with an adhesion of the cord to the sac.

The contents of the sac are a pellucid fluid of a specific gravity of about 1007. It is really the cerebrospinal fluid, and indeed, there is often a hydrocephalus associated with the spina bifida.

Spina bifida implies a dropsy of the structures of the cord, and different names are applied according to the share which the various structures take in the protrusion, these names being constructed on similar principles to those in use for the brain and its membranes. We have (1) Meningocele, or protrusion of the membranes only; (2) Meningo-myelocele, or protrusion of membranes and cord together; and (3) Syringo-myelocele, in which the protrusion obviously consists of a dilated and closed central canal. This form is also called Myelocystocele (Recklinghausen). Of these three forms the second is much the commonest, although the last-mentioned form is probably more frequent than has been usually supposed (Cleland).

The spinal cord in all forms of spina bifida is prolonged downwards as far as the seat of the tumour. As the latter is usually in the lumbosacral region, this implies that the cord occupies the entire length of the canal as it does in the earlier periods of foetal life. As the cord begins to retract within the canal in the fourth month the affection must be earlier in its origin than that period. It is of interest that even in cases of meningocele where the membranes alone are protruded this elongation of the cord occurs.

Fig. 343. - Section of a spina bifida of the lumbar region, a, b, Cutis and subcutaneous tissue; t, fascia; d, spinous processes; t, dura mater, which passes into sac and becomes attached to the skin at e'; f, arachnoid, which passes into sac forming its internal lining; g, spinal cord, which also enters the sac and becomes attached to the skin g', where it had a small opening; the attachment forms a dimple in the sac; n, n, spinal nerves which pass from the cord round to the anterior aspect of the sac so as to reach their normal places of issue from the spinal canal. (Virchow).

With the exception of elongation, the cord in a small number of cases is not involved. The fluid may be entirely behind it as in meningocele, and it may be little altered. In that case the nerves also will be in front of the protrusion.

In Syringo-myelocele the central canal is distended backwards, and although the internal lining of the sac is really the expanded central canal, yet the sac is, as in meningocele, behind the nerves and the greater part of the cord.

In the majority of cases, however, comprising the Meningo-myelo-celes, the spinal cord is actually involved in the sac (see Fig. 343), passing into it and attached to its wall, thus presenting various malformations and dislocations. The nerve-roots also which come oft' from the part of the cord involved take origin within the sac, and traverse it in order to reach their foramina. The posterior roots are necessarily more involved than the anterior. Sometimes the nerves take origin from the posterior wall of the sac, and the latter may present externally a double row of slight depressions corresponding with £his origin.

Spina Bifida Occulta

This term was first applied by Recklinghausen to an interesting form in which, without a tumour externally, there is elongation of the cord and defect of the vertebral arches. He supposes that there was here an early meningocele, which had subsequently shrunk. An important peculiarity in this form is the existence within the spinal canal, and in contact with the cord, of adipose and fibrous tissue and striated muscle, which may be in such quantity as to form a distinct tumour (myo-fibro-lipoma). The muscle is in bundles like those of the multifidus spinae, and Recklinghausen supposes that it may have arisen by a dislocation inwards of parts of this muscle through the defectively formed vertebral arches. Another peculiarity is the existence of an excessive growth of hair over the concealed spina bifida. It is not improbable that such lesions may be not infrequent. The existence of a tuft of hair in the lumbar region, which sometimes resembles a tail, should call attention to the condition of the arches of the vertebra? and this may reveal a spina bifida occulta. This form of spina bifida, like that in which a manifest tumour exists, may be associated with lesions of the cord resulting in paralysis.

The origin of spina bifida is to be referred to foetal life. Looking to the series of forms of lesion from completely open spina bifida with anencephalus to meningocele, it seems necessary to connect the affection with dropsy of the cerebrospinal canal. A further confirmation of this is the frequent co-existence of hydrocephalus. It can scarcely be supposed that a mere dropsy of the membranes, and still less a simple defect of the arches of the vertebrae, would fix the cord in the foetal position, so that we are induced to regard the lesion as primarily one of the cord itself. There may be a very early dropsy interfering with the closure of the canal, and so leading to rhachischisis. But after the closure there may be a dropsy leading to a local distension which may by and by rupture. If it does not rupture then there may be a spina bifida having the form of a syringo-myelocele. If it does rupture then the meningocele or the meningo-myelocele will result. The aperture may be ultimately a very narrow one or may become obliterated, and the central canal may form and even be of normal character. As a general rule, however, the fluid in the sac communicates freely with the cerebro-spinal fluid, and sudden withdrawal of the former sometimes leads to serious cerebral symptoms from the reduction of the cranial contents.

Literature

Hydrocephalus - Leubuscher, Path. d. Hirnkrank., 1854; Huguenin, (with full literature) in Ziemssen's Handb., xi., 1; Wilks, Guy's Hosp. Rep., 1860. Hydrorrhachis, etc. - Leyden, Virch. Arch., lxviii.; Langhans, do., lxxxv.; Krauss, do., c.; Schultze, do., cii.; Charcot, Lecons du Mardi, 1890; Gowers, Dis. of nerv. syst., ii., 1899; Hoffmann, Deut. Zeit. f. Nervenheilk., 1892; Schlesinger, Die Syringomyelie, 1897; Isaac Bruhl, Contrib. a 1'etude de la syringomyelic, 1890. Spina bifida - Forster, Missbildungen, 1865; Virchow, Geschwulste, i. and ii.; Banke, Jahrb. d. Kinderheilk., xii.; W. Koch, Mittheilungen, 1881; Morton, On spina bifida, 2nd ed., 1887; Cleland, in Morton, p. 32, also Jour, of Anat. and Phys., xvii., 257; Bep. to Clin. Soc. of London, 1885, xviii., 339; Recklinghausen, Virch. Arch., cv., 243 and 374 (with full literature); Bland Sutton, Lancet, 1887 and 1888.