Filar cyst

Sacral Dimple in a Neonate • Xray of the Week 2016 • Week #23

This neonate had an ultrasound of the lumbar spine to evaluate a sacral dimple. What is the abnormality? What is the significance of this finding?

Above image: Sagittal ultrasound image of the lumbar spine in 1 day old female showing a well-defined, fusiform shaped cystic lesion in the midline within filum, just inferior to the conus medullaris. This is typical for a benign filar cyst.

Filar cyst, also known as ventriculus terminalis, is seen in up to 12% of children aged less than 8 months. As in this case, ultrasound shows a well-defined, fusiform shaped cystic lesion in the midline within filum, just inferior to the conus medullaris. It is a normal variant that has no known clinical significance and does not require additional imaging. In fact, follow-up MRI usually fails to demonstrate the cyst.

References:

1. Irani N, et al. Isolated filar cyst on lumbar spine sonography in infants: a case-control study. Pediatr Radiol. 2006 Dec;36(12):1283-8.

2. Lowe L, et al. Sonography of the Neonatal Spine: Part 1, Normal Anatomy, Imaging Pitfalls, and Variations That May Simulate Disorders. AJR Am J Roentgenol 2007; 188:733–738

Kevin Rice, MD serves as the Medical Director of the Radiology Department of Valley Presbyterian Hospital in Los Angeles, California and is a Member of Renaissance Imaging Medical Associates. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015 Dr. Rice launched Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field.

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