LUMBAR EPIDURAL LIPOMATOSIS - THE Y-SIGN OF THECAL SAC COMPRESSION

Purpose. We have identified a specific sign of lumbar thecal sac compr ession seen in patients with symptomatic lumbar epidural lipomatosis. Recognition of this sign will aid with proper diagnosis of this unusua l disorder. Methods. Computerized Tomography (CT) and Magnetic Resonan ce Imaging (MRI) examinations of the lumbar spine performed in the eva luation of low back pain over a 24 mo period demonstrated nine patient s with excessive fat in the epidural space. Myelography was performed on five of these patients. Detailed analysis of the shape and degree o f thecal sac compression was made. Results. Eight of the nine patients with epidural lipomatosis demonstrated a characteristic type of theca l sac compression not seen with other spinal disorders. On cross secti onal imaging, the thecal sac has a striking stellate appearance with t hree rays emanating from a central core. This produces a trifid shape resembling the letter ''Y'': In two patients scanned following subsequ ent surgical removal of the epidural fat, the thecal sac had resumed i ts normal configuration. Conclusion. A seemingly specific and easily r ecognized type of compression of the thecal sac may occur with lumbar epidural lipomatosis. This creates a trifid appearance of the thecal s ac; we have termed this the ''Y'' sign.