Fetal syringomyelia.

We explored the prevalence of syringomyelia in a series of 113 cases of fetal dysraphism and hindbrain crowding, of gestational age ranging from 17.5 to 34 weeks with the vast majority less than 26 weeks gestational age. We found syringomyelia in 13 cases of Chiari II malformations, 5 cases of Omphalocele/Exostrophy/Imperforate anus/Spinal abnormality (OEIS), 2 cases of Meckel Gruber syndrome and in a single pair of pyopagus conjoined twins. Secondary injury was not uncommon, with vernicomyelia in Chiari malformations, infarct like histology, or old hemorrhage in 8 cases of syringomyelia. Vernicomyelia did not occur in the absence of syrinx formation. The syringes extended from the sites of dysraphism, in ascending or descending patterns. The syringes were usually in a major proportion anatomically distinct from a dilated or denuded central canal and tended to be dorsal and paramedian or median. We suggest that fetal syringomyelia in Chiari II malformation and other dysraphic states is often established prior to midgestation, has contributions from the primary malformation as well as from secondary in utero injury and is anatomically and pathophysiologically distinct from post natal syringomyelia secondary to hindbrain crowding.

[Neuroembryologic considerations on the so-called malformative syringomyelia]. / Réflexions d'un neuro-embryologiste à propos de la syringomyélie dite malformative.

Modern neuroradiological techniques can evidence the presence of liquid-filled spaces within the spinal cord, called syringomyelia. These lesions may be associated with numerous causes, the most frequent of which is an abnormality of the shape of the posterior fossa. Neuropathological analysis of these cavities demonstrates whether they are completely lined by ependymal cells or not. Comparing neuropathological and embryological data suggests that syringomyelia is a secondary deformation affecting a normally-formed spinal cord. The unique case in which such a cavity is really a primary malformation is the so-called myelocytocele. The most frequently encountered lesion associated with syringomyelia is the Chiari abnormality (either type I or II). In this case, the size of the posterior fossa is too small whereas neural elements are normal. Since Chiari abnormality may be familial, some genes are likely to be involved for its generation. In experimental animals, it has been shown that genes belonging to the Hox family or the Mhox gene control the development of the final shape of the occipital bone. Syringomyelia is thus a secondary event affecting the spinal cord and due to a distant cause.

Anatomical basis of syringomyelia occurring with hindbrain lesions.

Hindbrain lesions that distort or compress the cervicomedullary junction are commonly associated with syringomyelia. As a basis for discussing pathogenetic mechanisms, the upper end of the central canal of the spinal cord was examined histologically in six aborted fetuses and 14 adults dying of natural causes; the results were correlated with magnetic resonance images in 40 normal subjects. The central canal of the medulla, which extends from the cervicomedullary junction to the fourth ventricle, was found to migrate dorsally, elongate in dorsoventral diameter, and dilate beneath the tip of the obex to form a large, everted aperture. This opening communicates directly with the subarachnoid space through the foramen of Magendie and is indirectly continuous with the main body of the fourth ventricle. In adults, the aperture of the central canal is located approximately 1.0 cm below the tela choroidea inferior and 3.5 cm below the midpoint of the fourth ventricle. Analysis of magnetic resonance imaging scans in 45 patients with syringomyelia and simple hindbrain lesions revealed two patterns of cavity formation: 1) lesions that obstructed the upper end of the central canal or its continuity with the subarachnoid space produced a noncommunicating type of syringomyelia; and 2) lesions that obstructed the basilar cisterns or the foraminal outlets of the fourth ventricle produced a communicating type of syringomyelia (hydromyelia) in association with hydrocephalus. Evidence is presented that syrinxes occurring with hindbrain lesions are not caused by a caudal flow of cerebrospinal fluid from the fourth ventricle into the central canal of the spinal cord.

Syringomyelia: a brief review of ontogenetic, experimental and clinical aspects.

The generally accepted definition of syringomyelia is that it is a chronically progressive illness characterized by the presence of cavities or syrinxes in the spinal cord. As manifold as the terminology of syringomyelia are the hypotheses of the etiology. Nowadays with MRI without and with gadolinium it is possible to recognize intramedullar cavities safely, the MR especially the cine-MR provides information on pathophysiological details of the flow and intracavitary pressure dependent pulsations of the CSF. Animal models and the findings of own experimental studies have enabled us to study a form of syringomyelia which very closely resembles that brought about by dysrhaphic malformations in the human being and to examine the effectiveness of certain types of surgical therapy. In this paper the term syringomyelia is only used for dysrhaphic cavities in the medulla. After our experience with 61 patients with syringomyelia now we perform the operative decompression of the craniocervical transition as the first step in the operative treatment of the progressive syringomyelia combined with severe craniocervical malformations. In cases with insufficient treatment response we suggest the syringoarachnoid shunting of persisting large intramedullar cavities.

[Arguments in favor of the genetic origin of malformed syringohydromyelic pictures]. / Arguments en faveur de l'origine génétique des tableaux malformatifs syringohydromyéliques.

After a critical analysis of the criteria usually used for arguing in favor of the hydrodynamic determinism of the syringohydromyelic malformations, the authors report convincing data according to which such dysmorphic status would be the result of abnormalities in the genetic programs of the morphogenesis of the central canal.