Radiographic Assessment on Magnetic Resonance Imaging after Percutaneous Endoscopic Lumbar Foraminotomy

Abstract

Percutaneous endoscopic lumbar foraminotomy (ELF) is a novel minimally invasive technique used to treat lumbar foraminal stenosis. However, the validity of foraminal decompression based on quantitative assessment using magnetic resonance imaging (MRI) has not yet been established. The objective of this study was to investigate the radiographic efficiency of ELF using MRI. Radiographic changes of neuroforamen were measured based on pre- and postoperative MRI findings. Images were blindly analyzed by two observers for foraminal stenosis grade and foraminal dimensions. The intraclass correlation coefficient (ICC) and k statistic were calculated to determine interobserver agreement. Thirty-five patients with 40 neuroforamen were evaluated. The mean visual analog scale (VAS) score improved from 8.4 to 2.1, and the mean Oswestry disability index (ODI) improved from 65.9 to 19.2. Overall, 91.4% of the patients achieved good or excellent outcomes. The mean grade of foraminal stenosis significantly improved from 2.63 to 0.68. There were significant increases in the mean foraminal area (FA) from 50.05 to 92.03 mm², in mean foraminal height (FH) from 11.36 to 13.47 mm, in mean superior foraminal width (SFW) from 6.43 to 9.27 mm, and in mean middle foraminal width (MFW) from 1.47 to 78 mm (P < 0.001). Interobserver agreements for preoperative and postoperative measurements were good to excellent with the exception of SFW. In conclusion, foraminal dimensions and grades of foraminal stenosis significantly improved after ELF. These findings may enhance the clinical relevance of endoscopic lumbar foraminal decompression.

Keywords: endoscopic; foraminotomy; interobserver agreement; magnetic resonance imaging.

Fig. 1

Schematic illustration of the surgical procedure showing the extraforaminal approach for foraminal decompression (A), foraminal unroofing by using a burr under endoscopic control (B), and full-scale foraminal soft tissue decompression by using various endoscopic instruments (C), resulting in free mobilization of the exiting nerve root (D).

Fig. 2

Grade of foraminal stenosis on T2-weighted sagittal lumbar magnetic resonance images. (A) Grade 0 refers to the absence of foraminal stenosis. (B) Grade 1 refers to mild foraminal stenosis showing perineural fat obliteration in two opposing directions (vertical or transverse). (C) Grade 2 refers moderate foraminal stenosis showing perineural fat obliteration in the four directions without morphologic changes in the nerve root. (D) Grade 3 refers to severe foraminal stenosis showing nerve root collapse or morphologic change in the nerve root.

Fig. 3

Measurement of foraminal dimensions on T2-weighted sagittal lumbar magnetic resonance images. 1. Foraminal height (FH). 2. Superior foraminal width (SFW). 3. Middle foraminal width (MFW). 4. Posterior disc height (PDH).

Fig. 4

Illustrated case of an 81-year-old female patient. Preoperative T2-weighted sagittal magnetic resonance image showing severe foraminal stenosis (grade 3) at L5-S1 level on the right side (A). Postoperative T2-weighted sagittal magnetic resonance image showing full-scale foraminal decompression (grade 1) after percutaneous endoscopic lumbar foraminotomy (B).

Fig. 5

Illustrated case of a 67-year-old male patient. Preoperative T2-weighted sagittal magnetic resonance image showing severe foraminal stenosis with disc herniation at L4–5 level on the right side (A). Postoperative T2-weighted sagittal magnetic resonance image showing full-scale foraminal decompression (grade 1) after percutaneous endoscopic lumbar foraminotomy (B).