Table 1.

Characteristics of the included studies and patient demographics

Study, year	Study type	Level of evidence	Number of total subjects (Incidental/Intentional)	Number of subjects included in the systematic review (Incidental/Intentional)	Mean age (years)	Sex (M/F)	Indication for surgery
Takenaka et al, 201917	Retrospective cohort	2	429 (429/0)	354 (354/0)	69.7 ± 12.7	206/223	Disk herniation, Scoliosis, Spinal canal stenosis, Spondylolisthesis
Montano et al, 201818	Prospective cohort	2	35 (0/35)	35 (0/35)	58.1 ± 15.6	14/21	Ependymoma, Ganglioglioma, Hemangioma, Hemangioblastoma Meningioma, Schwannoma
Arnautovic et al, 201619	Case series	4	40 (0/40)	37 (0/37)	57.4 ± 17.3	11/29	Astrocytoma, Breast metastasis, Ependymoma, Hemangioblastoma, Meningioma, Myxopapillary, Schwannoma
Kamenova et al, 201620	Retrospective cohort	2	69 (69/0)	69 (69/0)	72.2 ± 12.8	35/34	Disk herniation, Spinal canal stenosis
Masuda et al, 201621	Case series	4	75 (22/53)	75 (22/53)	57.1	34/41	Epidural tumor, Intradural extramedullary tumor, Spinal canal stenosis, Metastatic spinal tumor, Ossification of ligamentum flavum, Spinal cord hernia, Spinal deformity, Spondylolisthesis, Spondylotic myelopathy, Subarachnoid cyst
Jo et al, 201522	Case series	4	15 (15/0)	15 (15/0)	42.2 ± 8.6	12/3	Ankylosing spondylitis
Grannum et al, 201423	Case control	3	28 (28/0)	13 (13/0)	50.8	14/14	Spinal canal stenosis
Tan et al, 201424	Case series	4	23 (0/23)	23 (0/23)	54.4 ±12.6	8/15	Congenital fatty filum, Congenital meningocele, Ependymoma, Lymphoma, Meningioma, Schwannoma, Spinal dural arteriovenous fistula, Tarlov cyst
Anderson et al, 201325	Case series	4	50 (50/0)	50 (50/0)	58.9	28/22	Adjacent segment degeneration, Cauda equina syndrome, Herniated disk, Scoliosis, Spinal canal stenosis, Spondylolisthesis
Sun et al, 201226	Retrospective cohort	2	85 (85/0)	85 (85/0)	54.3	44/41	Ossification of ligamentum flavum
Hodges et al, 199927	Case series	4	20 (20/0)	20 (20/0)	58.1 ± 15.9	7/13	NA
Total			869 (718/151)	776 (628/148)		869 (413/456)

NA: not available