Postoperative Spinal Subdural Lesions Following Lumbar Spine Surgery: Prevalence and Risk Factors

Abstract

Study design: Retrospective case-control study.

Purpose: To clarify the prevalence and risk factors for spinal subdural lesions (SSDLs) following lumbar spine surgery.

Overview of literature: Because SSDLs, including arachnoid cyst and subdural hematoma, that develop following spinal surgery are seldom symptomatic and require reoperation, there are few reports on these pathologies. No study has addressed the prevalence and risk factors for SSDLs following lumbar spine surgery.

Methods: We conducted a retrospective analysis of the magnetic resonance (MR) images and medical records of 410 patients who underwent lumbar decompression surgery with or without instrumented fusion for degenerative disorders. SSDLs were classified into three grades: grade 0, no obvious lesion; grade 1, cystic lesion; and grade 2, lesions other than a cyst. Grading was based on the examination of preoperative and postoperative MR images. The prevalence of SSDLs per grade was calculated and risk factors were evaluated using multivariate logistic regression analysis.

Results: Postoperative SSDLs were identified in 123 patients (30.0%), with 50 (12.2%) and 73 (17.8%) patients being classified with grade 1 and 2 SSDLs, respectively. Among these, one patient was symptomatic, requiring hematoma evacuation because of the development of incomplete paraplegia. Bilateral partial laminectomy was a significantly independent risk factor for SSDLs (odds ratio, 1.52; 95% confidence interval, 1.20-1.92; p<0.001). In contrast, a unilateral partial laminectomy was a protective factor (odds ratio, 0.11; 95% confidence interval, 0.03-0.46; p=0.002).

Conclusions: The prevalence rate of grade 1 SSDLs was 30%, with no associated clinical symptoms observed in all but one patient. Bilateral partial laminectomy increases the risk for SSDLs, whereas unilateral partial laminectomy is a protective factor.

Keywords: Arachnoid cysts; Complications; Risk factor; Spinal subdural hematoma; Surgery.

Fig. 1. Magnetic resonance imaging (MRI)-based grading system for the diagnosis of spinal subdural lesions (SSDLs) based on preoperative to postoperative changes within the dura mater. The three SSDL grades are depicted.

Fig. 2. An illustrative case of “grade 0” spinal subdural lesion (SSDL) according to our grading system. There was no evidence of postoperative changes in the dura mater on T2-weighted sagittal or axial magnetic resonance (MR) images. (A) preoperative T1-weighted sagittal MR image, (B) preoperative T2-weighted sagittal MR image, (C) preoperative T2-weighted axial MR image, (D) postoperative T1-weighted sagittal MR image, (E) postoperative T2-weighted sagittal MR image, and (F) postoperative T2-weighted axial MR image.

Fig. 3. An illustrative case of “grade 1” spinal subdural lesion (SSDL) according to our grading system. Space-occupying lesion (SOL) was identified within the dura mater. The signal intensity of SOL was equivalent to that of cerebrospinal fluid (T1 hypo-intensity/T2 hyper-intensity). These SOLs are considered arachnoid cysts. (A). preoperative T1-weighted sagittal magnetic resonance (MR) image, (B) preoperative T2-weighted sagittal MR image, (C) preoperative T2-weighted axial MR image, (D) postoperative T1-weighted sagittal MR image, (E) postoperative T2-weighted sagittal MR image, (F) postoperative T2-weighted axial MR image, (G) magnified postoperative T1-weighted sagittal MR image, and (H) magnified postoperative T2-weighted sagittal MR image. Arrows indicate fluid collection within the dura mater.

Fig. 4. An illustrative case of “grade 2” spinal subdural lesion (SSDL) according to our grading system. Space-occupying lesion (SOL) was identified within the dura mater. The signal intensity of SOL was different from that of cerebrospinal fluid. These SOLs are more likely to be spinal subdural hematomas than arachnoid cysts. (A) Preoperative T1-weighted sagittal magnetic resonance (MR) image, (B) preoperative T2-weighted sagittal MR image, (C) preoperative T2-weighted axial MR image, (D) postoperative T1-weighted sagittal MR image, (E) postoperative T2-weighted sagittal MR image, (F) postoperative T2-weighted axial MR image, (G) magnified postoperative T1-weighted sagittal MR image, and (H) magnified postoperative T2-weighted sagittal MR image. Arrows indicate fluid collection within the dura mater.

Fig. 5. (A) Magnetic resonance image taken on postoperative day 4, with the T1-weighted sagittal image showing a large hypointense posterior collection within the dural sac from approximately T10 to S1. (B) T2-weighted sagittal image showing hyper-intensity within the same collection. (C) T2-weighted axial image taken at the L2–L3 level showing anterior displacement and compression of the cauda equina.

Fig. 6. (A) Intraoperative photograph showing an extensive mass of clotted blood that was identified when the dura mater was opened. (B, C) Following en bloc evacuation of the clotted blood, the distended normal arachnoid sac was exposed. (D) Fenestration of the arachnoid membrane was performed.

Fig. 7. Magnetic resonance (MR) image obtained on postoperative day 2 following revision surgery. (A, B) T1-and T2-weighted sagittal MR images showing a decrease in the volume of the posterior compartment. (C) T2-weighted axial MR image taken at the L2–L3 level confirming the decompression of the cauda equina.