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

INTRODUCTION

Cauda equina syndrome (CES) is rarely seen in patients following lumbar surgery.[1,3,4] Here, we present four patients who, following L5S1 posterior decompressions, developed CES uniquely attributed to marked engorgement of the ventral epidural venous plexus documented on magnetic resonance images by the “convexity sign,” CES resolved spontaneously in three patients, but warranted a laminoplasty- decompression in the fourth.

CASE PRESENTATION

Four patients, ranging in age from 54 to 70, underwent lumbar decompressive procedures (three patients), and/or lumbar fusions [Table 1]. Postoperatively, between 1 and 4 days, all began to exhibit the following CES symptoms and signs; pain, perineal sensory loss, and dysuria. Postoperative MR studies revealed the “convexity sign” defined as a space ventral to the dural sac, similar to a convex lens, attributed to engorgement of the ventral epidural plexus. This resulted in marked ventral compression of the cauda equina [Figures 1-4 and Table 1].

Table 1:: Summary of four cases of CES attributed to ventral venous engorgement.

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Figure 1:: Magnetic resonance images of Case 1 (a) spondylolisthesis was present at the L5-S1 level, and the dural sac terminated at S1. (b and c) The postoperative MR showed the dorsal shift of the thecal sac (white arrow heads) attributed to the ventrally engorged epidural venous plexus (a white arrow and dotted line; i.e., the “convexity sign”). (d) Seven years postoperatively, the ventrally engorged epidural venous plexus could still be seen.

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Figure 2:: Magnetic resonance images of Case 2 (a) lumbar spinal canal stenosis was observed at the L4-L5 level. (b and c) The postoperative MR revealed ventral dural sac compression (white arrow heads) attributed to the engorged ventral epidural venous plexus (a white arrow and dotted line; that is, the “convexity sign.” (d) Six months later, the MR demonstrated a reduction in ventral compression, but not full resolution.

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Figure 3:: Magnetic resonance images of case 3 (a) lumbar spinal canal stenosis was observed at the L4-L5 level, and the dural sac terminated at S1. (b and c). Two years later, the follow-up MR still showed residual ventral epidural venous compression (white arrow heads/white arrow and dotted line).

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Figure 4:: Magnetic resonance images of Case 4 (a) the dural sac terminated at S1 level. (b and c) Postoperative MR images revealed ventral compression of dural sac (white arrow heads) due to the engorged ventral epidural venous plexus (a white arrow and dotted line). (d) After laminoplasty and coagulation of the ventral epidural venous plexus, the dural sac ventral compression was relieved.

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DISCUSSION

We describe four cases of CES following posterior lumbar decompression surgery at the L5-S1 level. TCES in all cases was attributed to engorgement of the ventral epidural venous plexus diagnosed on MR by the “convexity sign.” We previously and again here reported a postoperative CES case attributed to an engorged ventral venous plexus (i.e., Case 4 in this study); this case was successfully treated with a laminoplasty that included coagulation of the engorged ventral venous plexus.[2] However, in three cases, because of prior laminectomies, secondary laminoplasty was not a therapeutic option; fortunately CES resolved spontaneously.

CES following lumbar discectomy was described by McLaren and Bailey, and they elucidated that insufficient bony removal could result in postoperative CES.[3] Nerve root ischemia due to postoperative venous congestion was hypothesized as a cause of postoperative CES. Additional decompression surgery within 48 h was recommended to resolve postoperative CES.[1] Adequate resolution of preoperative spinal stenosis lesion, better selection of surgical instruments, and avoidance of dura tear and postoperative hematoma are also mandatory to prevent postoperative CES.[4]

CONCLUSION

Neurosurgeons should be aware that postoperative CES may develop due to marked engorgement of the ventral epidural venous plexus after posterior decompression surgery at the L5-S1 level.