Cauda equina syndrome after L5-S1 posterior decompression surgery showing a “convexity sign” caused by engorgement of the ventral epidural venous plexus: A case series

BACKGROUND: Cauda equina syndrome (CES) following posterior lumbar decompression is rare. Here, we present four postoperative cases of L5S1 surgery resulting in CES attributed to engorged ventral epidural veins that decreased spontaneously in three cases, while the fourth warranted a laminoplasty. CASE DESCRIPTION: Four patients underwent posterior lumbar decompressions at the L5-S1 level, but developed postoperative symptoms/signs of CES. Interestingly, in all four cases, cauda equina compression was attributed to engorgement of the ventral epidural venous plexus documented on magnetic resonance images (MRI) by the “convexity sign.” Postoperatively, three patients’ CES compression decreased spontaneously, but one required a laminoplasty. CONCLUSION: Postoperative CES occurred in four patients undergoing L5-S1 lumbar surgery. This deficit was attributed to marked engorgement of the ventral epidural plexus (i.e., yielding the “convexity sign” on MRI) that resolved spontaneously in three patients, but warranted a laminoplasty in the fourth.