Cyst of the medullary conus: malformative persistence of terminal ventricle or compressive dilatation?

Abstract

The ventriculus terminalis is a cavity situated at the level of the conus medullaris, enclosed by ependymal tissue and normally present as a virtual cavity or as a mere ependymal residue. In rare cases, and almost exclusively in pediatric age, the ventriculus terminalis may be visualized by radiological investigations, either by sonography or MRI, and represents a transient finding in children under 5 years of age. In pathological conditions, a cyst of the conus medullaris is probably the result of a persistent ventriculus terminalis and is usually described in children in association with a tethered cord; in a very limited number of cases, it has been described in adults whose clinical symptoms consist of neurological and/or sphincter disturbances not associated with other pathologies. The authors describe the case of a 42-year-old female with a cyst of the conus whose only symptom was imperious minction; she had been suffering from these urinary disorders for many years. The patient was not operated on because the clinical situation remained stable, without modifications of the MRI in follow-up over a 6-year period. The authors therefore suggest that in adult patients, a cyst of the conus medullaris is probably an expression of malformative persistence of the fifth ventricle and does not necessarily have a progressive evolution.

Fifth ventricle: an unusual cystic lesion of the conus medullaris

“…[1][2][3][4][5][6][7] The process of neurulation, which begins at 3 weeks of embryonic age, leads to the formation of the neural tube by a progressive fusion of the lateral edges of the neural plate starting from the level, of the third and fourth somite. From this level, the fusion process progresses at the same time cephalad and caudad.…”

“…The final stage is characterized by necrosis processes that result in dilatation of the portion of the ependymal canal located at the level of the conus medullaris, forming the fifth ventricle and a fibrous structure called the filum terminalis into which the ventriculus terminalis may extend. 2,3,4,6 During the first 5 years of life, evidence of a fifth ventricle not accompanied by other pathologies is, according to Coleman et al, 3 a frequent finding that does not have pathological significance.…”

“…2,5 The fact that the development process of the fifth ventricle is extremely variable means that there may be either a single cavity directly communicating with the central canal of the ependyma (more frequent in pediatric age) or an isolated cystic cavity of the spinal canal. The different morphological entities observed in both adults and children could merely be variants of the normal process of canalization and could therefore be attributed to a continuum of evolution of the conus medullaris.…”

“…Other factors contributing to the lesion's enlargement would be fibrotic and arachnoiditic processes, secondary to post-traumatic meningeal hemorrhages, and transcystic pressure gradient modifications caused by post-traumatic stenosis and deformities of the vertebral canal. 2 However, in most cases of the fifth ventricle described in the literature, there is no history of trauma.…”

“…Currently, most of the authors [1][2][3][4][5][6][7] believe that isolated cystic dilatation of the fifth ventricle is due to the persistence of this lesion in adulthood and to the abnormal closure of the communication between the ventriculus terminalis and the central canal by ependyma (disembryogentic theory).…”