Angle of covered self-expandable metallic stents after placement is a risk factor for recurrent biliary obstruction

Table 1 Baseline characteristics of patients and treatment

Baseline characteristic		n = 87
Age (IQR, yr)		63.5 (26.0-68.0)
Sex, n (%)	Male	55 (63.2)
	Female	32 (36.8)
ASA-PS, n (%)	1	24 (27.6)
	2	44 (50.6)
	3	19 (21.8)
Primary disease, n (%)	Pancreatic cancer	58 (66.7)
	Bile duct cancer	9 (10.3)
	Gallbladder cancer	2 (2.3)
	Ampullary cancer	2 (2.3)
	Duodenal cancer	2 (2.3)
	Other cancers	14 (16.1)
Clinical stage, n (%)	II	3 (3.5)
	III	9 (10.3)
	IV	75 (86.2)
Chemotherapy, n (%)	Yes	48 (55.2)
Radiotherapy, n (%)	Yes	11 (12.6)
Total bilirubin level (IQR, mg/dL)		3.8 (2.1-7.7)
Length of stricture (IQR, mm)		31.5 (21.8-39.3)
Total procedure time (IQR, min)		32.0 (24.5-48.5)
EST, n (%)	Yes	60 (69.0)
CSEMS type (1), n (%)	Partially	38 (43.7)
	Fully	49 (56.3)
CSEMS type (2), n (%)	Laser-cut	6 (6.9)
	Braided	81(93.1)
Length of CSEMS (cm), n (%)	4	3 (3.5)
	5	1 (1.1)
	6	44 (50.6)
	7	10 (11.5)
	8	29 (33.3)
Diameter of CSEMS (mm), n (%)	6	3 (3.5)
	8	3 (3.5)
	10	81 (93.0)
Angle of CSEMS (IQR, °)		146.0 (134.5-156.5)

Other cancers include cancers of the stomach, colon, small intestine, liver, kidney, breast, and cervix, leiomyosarcoma, and malignant melanoma. ASA-PS: American Society of Anesthesiologist Physical Status classification; EST: Endoscopic sphincterotomy; CSEMS: Covered self-expandable metallic stents; IQR: Interquartile range.

Table 2 Short- and long-term results, adverse events, cause of recurrent biliary obstruction, and reintervention

Classification		n (%)
		n = 87
Technical success		87 (100.0)
Functional success		72 (82.8)
Adverse event		9 (10.3)
	Pancreatitis	9 (10.3)
	Severe	1 (1.2)
	Moderate	5 (5.7)
	Mild	3 (3.4)
	Cholangitis	0 (0.0)
	Cholecystitis	0 (0.0)
	Other complications	0 (0.0)
		n = 18
RBO		18 (100.0)
	Sludge formation or food impaction	11 (61.1)
	Tumor overgrowth	5 (27.8)
	Migration	2 (11.1)
	Tumor ingrowth	0 (0.0)
Reintervention		18 (100.0)
	Metallic stent	9 (50.0)
	Sweep	5 (27.8)
	Plastic stent	3 (16.7)
	Not success	1 (5.5)

Other complications include bleeding, perforation, etc. RBO: Recurrent biliary obstruction; TRBO: Time to recurrent biliary obstruction; IQR: Interquartile range.

Table 3 Baseline characteristics of patients and treatment (recurrent biliary obstruction group vs non-recurrent biliary obstruction group)

		RBO group (n = 18)	Non-RBO group (n = 69)	P value
Age (IQR, yr)		66.5 (61-77)	69 (63.5-77)	0.63
Sex, n (%)	Female	5 (27.8)	27 (39.1)	0.42
	Male	13 (72.2)	42 (60.9)
ASA-PS, n (%)	1	2 (11.1)	22 (31.9)	0.07
	2	9 (50.0)	35 (50.7)
	3	7 (38.9)	12 (17.4)
Primary disease, n (%)	Other cancers	8 (44.4)	21 (30.4)	0.28
	Pancreatic cancer	10 (55.6)	48 (69.6)
Clinical stage, n (%)	II	1 (5.6)	2 (2.9)	0.08
	III	4 (22.2)	4 (5.8)
	IV	13 (72.2)	63 (89.9)
Chemotherapy, n (%)	No	8 (44.4)	31 (44.9)	1.00
	Yes	10 (55.6)	38 (55.1)
Radiotherapy, n (%)	No	17 (94.4)	59 (85.5)	0.45
	Yes	1 (5.6)	10 (14.5)
Total bilirubin level (continuous, mg/dL)		2.7 (1.1-6.7)	4.4 (2.3-9.0)	0.07
Length of stricture (IQR, mm)		34.9 (25.9-47.2)	30.9 (21.4-37.8)	0.13
Total procedure time (IQR, min)		35.5 (25-50.8)	32.0 (24-47)	0.65
EST, n (%)	No	5 (27.8)	22 (31.9)	1.00
	Yes	13 (72.2)	47 (68.1)
CSEMS type (1), n (%)	Partially	9 (50.0)	29 (42.0)	0.60
	Fully	9 (50.0)	40 (58.0)
CSEMS type (2), n (%)	Laser-cut	1 (5.6)	5 (7.2)	1.00
	Braided	17 (94.4)	64 (92.8)
Length of CSEMS, n (%)	≤ 6 cm	8 (44.4)	40 (58.0)	0.55
	7 cm	3 (16.7)	7 (10.2)
	8 cm	7 (38.9)	22 (31.9)
Diameter of CSEMS, n (%)	6 mm	0 (0.0)	3 (4.4)	0.58
	8 mm	1 (5.6)	2 (2.9)
	10 mm	17 (94.4)	64 (92.8)
Angle of CSEMS (IQR, °)		135.5 (114.8-149.3)	149.0 (138.5-158)	0.01

ASA-PS: American Society of Anesthesiologist Physical Status classification; EST: Endoscopic sphincterotomy; CSEMS: Covered self-expandable metallic stents; IQR: Interquartile range; RBO: Recurrent biliary obstruction.

Table 4 Risk factors for recurrent biliary obstruction following covered self-expandable metallic stent placement by Cox proportional hazards analysis

		n	Case (%)	Univariate analysis		Multivariate analysis
				Unadjusted HR (95%CI)	P value	Adjusted HR (95%CI)	P value
Age (continuous, yr)		87	18 (20.7)	1.00 (0.95-1.04)	0.91
Sex	Female	32	5 (15.6)	1.00
	Male	55	13 (23.6)	1.44 (0.51-4.05)	0.49
ASA-PS	1	24	2 (8.3)	1.00
	2	44	9 (20.5)	2.59 (0.56-12.00)	0.23
	3	19	7 (36.8)	5.12 (1.06-24.81)	0.04	1.76 (0.85-3.62)	0.13
Primary disease	Others	29	8 (27.6)	1.00
	Pancreatic cancer	58	10 (17.2)	0.80 (0.31-2.05)	0.64
Clinical stage	II	3	1 (33.3)	1.00
	III	8	4 (50.0)	2.34 (0.26-21.22)	0.45
	IV	76	13 (17.1)	0.79 (0.10-6.18)	0.82
Chemotherapy	No	39	8 (20.5)	1.00
	Yes	48	10 (20.8)	1.13 (0.44-2.88)	0.80	1.02 (0.40-2.61)	0.97
Radiotherapy	No	76	17 (22.4)	1.00
	Yes	11	1 (9.1)	0.43 (0.06-3.24)	0.41
Total bilirubin level (continuous, mg/dL)		87	18 (20.7)	1.01 (0.99-1.03)	0.26
Length of stricture (continuous, mm)		87	18 (20.7)	1.03 (1.00-1.07)	0.10
Total procedure time (continuous, min)		87	18 (20.7)	1.00 (0.98-1.03)	0.75
EST	No	27	5 (18.5)	1.00
	Yes	60	13 (21.7)	1.19 (0.42-3.35)	0.75
CSEMS type (1)	Partially	38	9 (23.7)	1.00
	Fully	49	9 (18.4)	0.85 (0.34-2.15)	0.73
CSEMS type (2)	Laser-cut	6	1 (16.7)	1.00
	Braided	81	17 (21.0)	1.27 (0.17-9.73)	0.82
Length of CSEMS	≤ 6 cm	48	8 (16.7)	1.00
	7 cm	10	3 (30.0)	2.33 (0.61-8.89)	0.22
	8 cm	29	7 (24.1)	1.63 (0.64-4.14)	0.45
Diameter of CSEMS	< 10 mm	6	1 (16.7)	1.00
	≥ 10 mm	81	17 (21.0)	1.37 (0.18-10.47)	0.76
Angle of CSEMS (continuous, per 10°)		87	18 (20.7)	0.67 (0.51-0.87)	< 0.01	0.71 (0.54-0.92)	0.01

Data are presented as medians for continuous variables and as numbers for categorical variables. For categorical data, comparisons between groups were performed using the chi-squared test (or Fisher’s exact test, when necessary, because of small sample sizes), whereas continuous data were compared using Mann-Whitney U test. ASA-PS: American Society of Anesthesiologist Physical Status classification; EST: Endoscopic sphincterotomy; CSEMS: Covered self-expandable metallic stents; IQR: Interquartile range; HR: Hazard ratio; CI: Confidence interval.

Table 5 Details of patients who had recurrent biliary obstruction following covered self-expandable metallic stenting (< 130° group vs ≥ 130° group)

	< 130° group	≥ 130° group	P value
	n = 16	n = 71
RBO, n (%)	7 (43.5)	11 (15.5)	0.07
	n = 7	n = 11
Cause of RBO, n (%)	7 (100.0)	11 (100.0)
Sludge formation or food impaction	3 (42.9)	8 (72.7)
Tumor overgrowth	3 (42.9)	2 (18.2)
Migration	1 (14.2)	1 (9.1)
Tumor ingrowth	0 (0.0)	0 (0.0)
Elevated liver enzymes, n (%)	6 (85.7)	5 (45.5)

RBO: Recurrent biliary obstruction; CSEMS: Covered self-expandable metallic stents.