DISCUSSION
This kind of lesion was called an enterogenous cyst by Harriman in 1958, who described an anterior intradural cyst with respiratory epithelium.

Enterogenous cysts (EC) are rare mass lesions arising during notochordal development and resulting from entrapment of endodermal tissue between a segmentally split notochord.

More than 80% of EC are located in the spine, whereas only 10% to 15% are intracranial. They can occur at any age, from birth to fifth decade, but they are definitely more frequent after age 20 (1). Although all the levels may be involved in the spine, there is a slight predominance for the cervical spine, especially the lower levels.(2) There is a slight predominance in males, with male-to-female ratio 3:2.(3)

During the third week of embryogenic development, invagination and migration of cells at the primitive streak and node of the embryogenic disk result in the formation of the notochord and mesodermal germ layer. The notochord is located in the dorsal aspect of the embryogenic disk, anterior to the depression of the primitive streak. The depression deepens, yielding the neural groove and the neural crest infolding until the neural tube is closed. The neural tube closure starts in the region of the fourth somite (future cervical region) and continues in both cranial and caudal directions. The neural tube contains communications between the notochord and the yolk sac, and the amnion: these communications, referred to as the canals of Kovalevsky, normally involute about the 17^th day of embryologic life (4). Subsequently, notochord detaches from the underlying endoderm. If a communication persists, an abnormal split of notochord may occur; also a persistent adhesion between endoderm and ectoderm or between notochord and endoderm, resulting in a variety of malformations which depend on the ability of the notochordal abnormal development to repair.(5)

In our case, a bone defect was not seen on CT. A very thin linear hyperintensity in T2 and Proton density extended forward to end blindly; it can be compatible with a remnant of a fistulous connection corresponding to Kovalevsky canal.(6)

The MR has replaced CT and CT myelography although CT, done with thin sections, has an important rule to pick up abnormality in the bone. Usually the density of NE is isodense to CSF with no calcifications and no contrast enhancement. In our patient, some calcifications were present in the inferior part of a grossly round hypodense lesion.

The signal features are very variable and different patterns of signal have been described in the literature. Neurenteric cysts may be isointense to hyperintense relative to CSF on T2-weighted MR images. On T1-weighted MR images, most neurenteric cysts are isointense or slightly hyperintense relative to CSF . Occasionally, homogeneous, very bright signal intensity on T1-weighted MR images and/or low intensity on T2-weighted MR images may be seen. These signal characteristics are thought to correlate with protein content or hemorrhage within the cysts (3). The absence of contrast enhancement is usually reported, according with cystic nature of these lesions and their poor vascularization.

In our patient, a smooth intradural extra-axial lesion, slightly hyperintense in T2 and fairly hyperintense in PD to CSF was seen in front of the cervical-medullary junction. After gadolinium injection a small hyperintense

çPrevious

Next è