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Ventriculus terminalis

The ventriculus terminalis, often known as the 5th ventricle, is an ependymal-lined, anatomical remnant, positioned at the transition from the tip of the conus medullaris to the origin of the filum terminale. It represents the canalization and retrogressive differentiation of the caudal end of the developing spinal cord and regresses in size during the first weeks after birth. 

Radiographic features

Irrespective of the modality used to image the spine, a ventriculus terminalis in new borns appears as a cystic structure at the tip of the conus medullaris, extending over 8-10 mm and with a transverse diameter of 2-4 mm. Later in childhood it often remains visible as a tiny cystic structure but it is rarely identifiable in adults.

Related pathology

Abnormal persistence or cystic dilatation of the ventriculus terminalis (cyst of the medullary conus) can occur and may present symptomatically in adulthood with bladder or bowel sphincter disturbance.  

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