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Neuroradiology Case of the Week

Case 155

Loris Cedeno MD, Jeevak Almast, MD, Ravinder Sidhu, MD
and PL Westesson MD, DDS, PhD

Clinical Presentation: Patient is a 12-month-old male with right leg weakness and sacral dimple. MR has been requested to evaluate for occult spinal cord abnormality.

Radiological Findings: There is a spindle shaped cavity seen in the conus medullaris measuring about 2 cm in length and 3.5 mm in maximum diameter. There is no associated mass or abnormal enhancement. The conus terminates at the L1 level. There is no evidence of tethering of the cord. No intraspinal mass or lipoma seen. The lumbosacral vertebrae are normal in morphology (Fig. 1).

Diagnosis:  Ventriculus terminalis

Discussion: The ventriculus terminalis is a small ependyma-lined cavity in the conus medullaris. It is usually in continuity with the central canal. The ventriculus terminalis forms by the ninth week of gestation, but it does not achieve maximum dimension until after 2 1/2 years of life. The spinal cord is formed in two stages: neurulation (where there is closure of the neural tube), and canalization and retrogressive differentiation. Neurulation is completed by about 4 weeks which forms most of the spinal cord.
     Canalization is the process by which the neural tube develops caudal to the posterior neuropore which also elongates. The caudal end of the neural tube and the notochord blend to become an aggregate of undifferentiated cells called the caudal cell mass. Small vacuoles then develop within this small mass which coalesce (canalize) and eventually form an ependyma lined tube that usually fuses with the more rostral central canal. This widening in the distal conus is the ventriculus terminalis.

References:

1. Coleman LT, Zimmerman RA, Rorke LB. Ventriculus terminalis of the conus medullaris: MR findings in children. AJNR Am J Neuroradiol. 1995 Aug;16(7):1421-6. [Medline]
2. Barkovich AJ. Pediatric Neuroimaging, 4th Ed. Lippincott Williams & Wilkins 2004, pgs. 621-624.