SPINA. BFFIDA, or cleft-spine, is a disease commencing in festal life, and which consists in an imperfection of the posterior part of the spinal canal. It is almost always accompanied by an excessive secre tion of spinal fluid, and in these cases it may be regarded as a disease of the same kind affecting the spinal canal as that which, existing in the skull, constitutes hydrocephalus. The two are indeed not unfrequently coincident ; and spina bifida is sometimes called hydro rachia.
The arch of each vertebra [SKELETON, in NAT. HIST. Div.] is developed and ossified in two pieces which meet behind in the middle line at the base of the spinous process. This is also developed in two lateral portions which subsequently unite together and with the arch, so as to form the one piece of bone which we find in the adult closing in the back of the spinal canal. This development and union of the arches of the vertebrae goes on during an early period of festal life, while the spinal column is growing rapidly, and the fluid of the spinal canal and arachnid sac is being constantly secreted. If this fluid be secreted in an unnaturally large quantity before any or a part of the arches of the vertebra, are completely ossified, it may exert such pressure upon them as to separate their component parts, and produce a permanent aperture in the back of the spinal canal, through which a sac containing the, excess of fluid will protrude. Or if the develop ment and ossification of any or all of the arches take place more slowly than it should, then a secretion of not more than the ordinary quantity of fluid may suffice to keep them permanently open. A cleft spine will thus be produced without the watery tumour ; but the openness of the spine will generally in cases of this kind lead to the secretion of an unnatural quantity of the spinal fluid ; for it seems a general law that, other things being equal, the quantity of fluid secreted in each part is inversely proportionate to the resistance offered by the walls of the cavity into which it is poured.
Spina bifida Is almost always characterised by a tumour situated over the defective vertebrae, globular, elastic, and fluctuating, often attached by a narrowed base, and varying in size according to the extent of the fissure in the spinal canal. It is usually covered by healthy skin, and consists of the dura mater, and one or more of the other membranes of the spinal cord, protruded in a sac through the space between the separated arches, and filled by a clear serous fluid.
On pressing-such a tumour the patient may become insensible, or be convulsed ; for the fluid within it communicating with that within or around the brain and spinal chord, the pressure made upon it is felt with equal force by the whole of those organs. The parts of the body below the tumour are often paralytic, not from the pressure of the fluid, for that is equally diffused, but from disease of the cord coinci dent with that of the arches.
Spina bifida is most common in the lumbar and sacral regions, in which the vertebral arches are latest completed : it is most rare in the neck, and is there also most dangerous, because of the great number of nerves which, by the coincident disease of the spinal cord, may be paralysed. It does not commonly interfere with the general health : but by the friction to which, when the tumours are large, the skin is subjected, and by the distension produced by the increasing secretion of fluid, the sac is liable to inflame and ulcerate, till, exposing the spinal cord, or its membranes, death is produced by their inflamma tion ; or, the quantity of fluid secreted may be so great as to produce death by its pressure on the cord and brain, in a manner similar to that in which hydrocephalus often terminates.
In one of these modes, spina bifida, when accompanied by excessive secretion, almost always terminates fatally, though patients may survive with it for ten or even twenty years. Life may generally be prolonged by maintaining a gentle even pressure upon the tumour, so as to supply the necessary resistance to the effusion of more fluid. In a few cases a repeated evacuation of the fluid, and then firm pressure upon the sac, has been found successful; and lately, M. Tavignot has related some cases which he cured by slicing off the tumour, and instantly bringing together the edges of the mouth of the sac, and so holding them till they had united and formed a firm cicatrix.
That just described is by far the most common form of spina bifida; others more rare are those in which not the arches only, but the bodies of the vertebrx also are cleft, the two lateral portions in which each is developed being kept apart, so that a portion of the spinal canal is open in.front towards the cavity of the abdomen. Some differences of character also depend on the seat of the fluid secreted : it is generally in the sac of the arachnoid, but sometimes is in the tissue of the pia mater, or in both it and the sac, or, yet niece rarely, in the central canal of the spinal cord.