Radiologic signs of hydromyelia.

Abstract

Hydromyelia is a condition in which the central canal of the spinal cord is pathologically dilated, usually from the fourth ventricle to the lower end of the spinal cord. Although some authors have described syringomyelia and hydromyelia as being the same entity, with cases assigned to one category or another, according to whether or not the typical symptoms of syringomyelia were present during life, there is some justification for separating them pathologically and etiologically. The authors present 4 cases with observations which give a better understanding of this entity (3). Mechanical Theory of Hydromyelia Immediately after its closure, the neural tube of the normal embryo becomes distended because fluid forms within it more rapidly than it can escape through the semipermeable rhombic roof. Since this distention affects the central canal of the cord as well as the cerebral ventricles, it follows that both hydrocephalus and hydromyelia are physiologic in embryonal life. The term, hydrocephalomyelia, therefore describes this normal state. If adequate perforation of the rhombic roof does not occur during the critical six- to eight-week embryo period, fluid will not filter through it in sufficient quantity to dissect open the developing subarachnoid spaces. The central canal, which normally closes, would thus be maintained as a function of the increased ventricular fluid pressure, which in turn would cause distention of the spinal central canal. Case Reports Case I: M. W., a 55-year-old white woman, was first admitted to the Neurological Institute in 1960 with a history of eight years progressive spasticity of the legs and eighteen days urinary retention. One episode of fecal incontinence had also occurred. At the time of admission the patient was unable to stand. Neurological examination revealed a left Horner's syndrome with spastic quadriparesis and hyperreflexia, more marked on the right side. A probable sensory level was noted at C4. Plain films of the foramen magnum region disclosed partial assimilation of the first cervical vertebra into the occiput and moderate platybasia. There was no evidence of enlargement of the cervical spinal cord. A posterior fossa craniectomy and C1-C2 laminectomy showed that the foramen magnum was relatively tight. There was an Arnold-Chiari malformation, with the tonsils a moderate distance below the foramen magnum. The foramen magnum and upper cervical region were decompressed (Fig. 1). Postoperatively, the patient improved in strength to the point where she was able to walk and a catheter was not required. The patient was readmitted in June 1964, with a five-month history of increasing difficulty in walking, frequent urinary incontinence, and occasional fecal incontinence. Another myelogram at this time showed that the spinal cord was tethered to the dura posteriorly at C1, with definite enlargement of the cervical spinal cord consistent with hydromyelia.