Cysts associated with degeneration of the lumbar facet joints are commonly
encountered during routine lumbar endoscopy. They can be difficult to dissect and may
heighten the risk of nerve root injury when they are fibrotically attached. Many of these
cysts are extradural. Because of their highly inflammatory nature, they may be
associated with radicular symptoms even without associated mechanical compression
of the traversing or exiting nerve root of the symptomatic surgical level. These synovial
cysts may be acutely painful. Their related symptoms may be difficult to distinguish
from those caused by lumbar disc herniation or stenosis in the lateral spinal canal on
clinical examination. The endoscopic spine surgeon is often forced to deal with them to
complete the neural element decompression. What is less clear is what to do with
patients with sizeable isolated facet joint based cysts without much other clinical
pathology. The surgical indications and prognosticators of favorable clinical outcomes
with endoscopic surgery are less well understood. Therefore, the authors performed a
systematic analysis of their clinical series of patients they identified to have had
synovial cysts either on preoperative advanced imaging studies or on those they found
serendipitously during routine lumbar endoscopy. In total, 48 were identified in whom
removal of the extradural cyst was performed during routine transforaminal and
interlaminar endoscopy. The primary indication for surgery in these patients was
painful foraminal and lateral recess stenosis. The patients were divided into 26 females
and 22 males. The L4/5 level was the most frequent site of facet based cysts. It was
found in 26 patients (72.2%). The second most common site was the L5/S1 level in 8
patients (22.2%), followed by two patients (5.6%) at the L3/4 level. A single patient
had endoscopic decompression at the T9/10 level. Outcome analysis showed clinical
improvements in all patients. According to the modified Macnab criteria, 19/48
(39.6%) patients had excellent outcomes. Good and fair results were achieved in 18/48
(37.5%) and 11/48 (22.9%) patients, respectively. The observed VAS leg pain score
reductions were substantial and statistically significant (p < 0.000) from preoperative
8.06 ± 1.57 to postoperative 1.92 ± 1.49, and 1.77 ± 1.32 at final follow-up. One patient
had a recurrent disc herniation, and another patient did not improve. Two patients underwent fusion during the follow-up period. Patients with Fair outcomes had a
statistically significant association (p < 0.001) with facet instability as suggested by
axial T2-weighted MRI imaging findings of thickened ligamentum flavum, facet joint
hypertrophy, and a bright white fluid-filled joint gap of > 2 mm. Endoscopic resection
of extradural spinal cysts that nearly exclusively stem from degenerated lumbar facet
joints in skilled hands is feasible. Instability was one of the prognosticators of Fair
Macnab outcomes.
Keywords: Endoscopic decompression, Extradural cysts, Lumbar foraminal stenosis
