Aetiologies and prognosis of small bowel obstruction in virgin abdomen: a retrospective cohort study

Abstract

Background

Small bowel obstruction (SBO) in patients with a virgin abdomen (VA)—no prior abdominal surgery—remains understudied, with traditional assumptions favoring mandatory surgical exploration due to suspected non-adhesive etiologies like malignancy or hernias. However, emerging evidence suggests adhesions are also prevalent in SBO-VA, challenging this paradigm. This study investigates the etiologies, management outcomes, and prognostic factors of SBO-VA to guide evidence-based treatment strategies.

Methods

A retrospective analysis was conducted on 312 SBO-VA patients treated at a tertiary center from 2009 to 2020. Patients were categorized into immediate surgery (n = 124), delayed surgery (n = 45), or non-operative (n = 143) groups. Etiologies, imaging findings, surgical outcomes, and recurrence rates were analyzed.

Results

Adhesions, luminal obstructions, and neoplasms were the leading causes of SBO-VA. The surgical group (n = 169) had a 7.1% mortality rate, highest with volvulus and mesenteric ischemia. Bowel necrosis occurred in 32.5% of adhesive SBO cases, associated with peritonitis or mesenteric edema on CT. The non-operative group had a 4.9% mortality rate, with inflammatory diseases as the predominant suspected etiology. CT accurately predicted surgical findings in 60.1% of cases, with closed-loop signs and ascites indicating necrosis. Recurrence occurred in 23.5% of conservatively managed patients, often within four years.

Conclusion

SBO-VA exhibits diverse etiologies, with adhesions being the most common. Conservative management is feasible in select patients, particularly those with inflammatory conditions, while early surgery is critical for cases with signs of strangulation or ischemia. CT imaging plays a pivotal diagnostic role. Incorporating water-soluble contrast agents may optimize non-operative management. These advocate for tailored treatment strategies based on etiology and clinical risk stratification.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13017-026-00691-1.

Introduction

Small bowel obstruction (SBO) is a surgical emergency characterized by mechanical obstruction of the small intestine, which prevents the passage of intestinal contents. It accounts for approximately 50% of all emergency laparotomies, leading to significant in-hospital morbidity and substantial healthcare costs [1–4]. Notably, SBO can occur in patients with no prior abdominal surgery, a condition defined as SBO in the virgin abdomen (VA-SBO). Non-operative management, including bowel decompression, water-soluble contrast agents (WSCA), and fluid resuscitation, has been proven safe and effective in 70% of adhesive SBO (ASBO) cases [5]. Traditionally, mandatory surgical exploration has been preferred for VA-SBO, based on the assumption that most etiologies are non-adhesive, such as malignancy or hernias [6, 7]. However, recent studies, including a key WSES position paper, have indicated a high incidence of adhesions in VA-SBO patients [8–10], suggesting that ASBO management guidelines may be applicable to many VA-SBO cases. Importantly, though, the evidence from these prior studies is predominantly derived from Western cohorts.

Despite this progress, critical knowledge gaps remain, particularly in non-Western populations such as the Chinese. First, the etiological spectrum of VA-SBO in large Chinese cohorts is poorly characterized, as most existing data originate from European and North American populations [10–11]. Second, robust data on the long-term outcomes of conservatively managed VA-SBO patients are limited—especially regarding recurrence patterns and the reliability of assuming an adhesive cause after successful non-operative treatment. Third, while computed tomography (CT) is the gold standard for SBO diagnosis, its ability to predict VA-SBO etiologies and guide surgical decisions is inconsistent. More notably, which CT features predict intestinal necrosis in adhesive VA-SBO, a key factor for surgical risk assessment, has not been clearly established in non-Western settings [12–13].

Therefore, this study aims to characterize VA-SBO’s aetiological spectrum in a large Chinese single-center cohort, evaluate long-term outcomes of conservatively managed VA-SBO patients with a median follow-up of 37.9-month, assess the performance of CT in predicting VA-SBO aetiology and surgical need, and enhance diagnostic certainty of adhesive aetiology in conservatively managed patients via clinical and radiological factors. We seek to refine an evidence-based, China-tailored VA-SBO approach, framing our work as a complement to prior Western-focused studies rather than repetition, and emphasize individualized treatment based on aetiologies and patient-specific conditions over traditional mandatory laparotomy.

Materials and methods

Patients and data collection

From January 2009 to December 2020, 2098 consecutive patients with 2275 admissions who diagnosed with bowel obstuction were enrolled in the First Affiliated Hospital of Nanjing Medical University, P. R. China. For patients with multiple admissions, only the index admissions were included, the rest were used for follow-up analysis. The detailed medical records of those 2098 patients were collected and reviewed. Only patients without prior abdominal operations and with CT or surgical exploration confirmation of the diagnosis of SBO were included. In addition, patients with age less than 14 years were excluded in this study. The diagnosis of SBO was established if an attending surgeon documented interpretation of CT imaging and was in agreement with the diagnosis. Finally, 312 patients with SBO in virgin abdomen were included in this study. We further retrospectively analyzed the medical records of 312 patients who were scheduled for either surgical group or medical group. A total of 169 of these patients were classified into three treatment groups: an immediate surgery group, including 124 patients, where a decision to operate was made within 24 h of surgical review; a delayed surgery group that included 45 patients who were managed initially with non-operative intent but subsequently required surgical intervention; and a non-operative group comprising 143 patients who did not undergo surgery at any time point. The selecting process is summarised in Fig. 1.

Fig. 1.

Algorithm of selecting valid patients with small bowel obstruction in virgin abdomen. pts. patients, abd. Abdominal

Since no guidelines exist regarding the management of an SBO in patients with a virgin abdomen, whether patients had surgical or medical treatment was at the discretion of the attending surgeon [6]. The absence of previous abdominal surgery and the assumption of underlying pathology might have favored an operative approach in these patients. Being a retrospect study, the exact/in-detail reasoning for a final management approach was diffificult to extracted from the medical records. Conservative treatment included nasogastric tube insertion for decompression, with strict measurement of output. Patients were kept nil by mouth, intravenous fluid replacement was administered and electrolyte imbalances were corrected as required. Resolution of bowel obstruction was defined by the passage of flatus and stools, and when the symptoms and signs of obstruction abated. Of note, due to the hospital policy, no patient had ever attempted water-soluble contrast challenge. For surgical patients, intraoperative findings, including the etiologies of obstruction, intestinal necrosis, types of surgery and mortality within 30 days of admission, were compared. Diagnosis and features of computerized tomography (CT) studies were analysed and compared with the intraoperative findings. For medically-treated patients, their previous medical history and features of CT studies were analyzed to help to speculate the possible diagnosis. They were followed up either by telephone or outpatient department records after discharge. Any recurrence and treatments of the recurrence were recorded and analysed. The work has been reported in line with the STROCSS criteria [14].

Statistical analyses

Statistical analyses were performed with SPSS ver.25 (2017, IBM Corp.). Continous variables were reported as mean±standard deviation. Categorical variables were compared by Pearson’s χ² or Fisher’s exact test. P value < 0.05 was statistically significant.

Results

Demographic characteristics of patients with SBO-VA

In this study, a total of 312 patients with SBO-VA (119 females and 193 males) were enrolled in this study and analyzed retrospectively. According to the treatment strategy, the patients were divided into three groups: immediate surgery group (n = 124, surgical decision made within 24 h of admission), delayed surgery group (n = 45, initially managed conservatively but requiring subsequent surgical intervention), and non-operative group (n = 143, no surgical intervention throughout the treatment). The baseline characteristics of the three groups are detailed in Table 1. Briefly, the mean age of the immediate surgery group, delayed surgery group, and non-operative group was 60.7 ± 18.5 years, 61.5 ± 18.7 years, and 55.1 ± 20.5 years, respectively. The proportion of males was 56.5% (70/124) in the immediate surgery group, 71.1% (32/45) in the delayed surgery group, and 63.6% (91/143) in the non-operative group. The duration of symptoms differed significantly among the three groups, with the longest duration in the delayed surgery group (19.9 ± 29.0 days) and the shortest in the immediate surgery group (5.0 ± 6.5 days). Regarding radiological examinations, CT was the most commonly used modality in all three groups, with 62.1% (77/124) of patients in the immediate surgery group undergoing CT only, 46.7% (21/45) in the delayed surgery group, and 46.2% (66/143) in the non-operative group.

Table 1.

Patients demographics

	Immediate surgery	Delayed surgery	Conservative
	n = 124	n = 45	n = 143
Age (years)	60.7 ± 18.5	61.5 ± 18.7	55.1 ± 20.5
Male (%)	70(56.5)	32(71.1)	91(63.6)
Duration of symptoms (days)	5.0 ± 6.5 [0.3, 40]	19.9 ± 29.0 [0.5, 150]	7.8 ± 10.2 [0.3, 60]
Referral from other medical facility (%)	78(62.9)	25(55.6)	75(52.4)
History of previous episode (%)	10(8.1)	14(31.1)	35(24.5)
Radiology
Abdominal X-ray only	9(7.3)	4(8.9)	17(11.9)
CT only	77(62.1)	21(46.7)	66(46.2)
CT and abdominal X-ray	38(30.6)	20(44.4)	60(41.9)

Aetiology and management of patients with SBO-VA

The etiological distribution of SBO-VA patients across different treatment groups is summarized in Table 2. In the immediate surgery group, the top three etiologies were adhesions (34 cases, 27.4%), luminal occlusions (26 cases, 21.0%), and neoplasms (18 cases, 14.5%), followed by volvulus (12 cases, 9.7%), mesenteric ischemia (11 cases, 8.9%), and internal hernia (6 cases, 4.8%). In the delayed surgery group, neoplasms (11 cases, 24.4%) and luminal occlusions (11 cases, 24.4%) were the most common causes. In the non-operative group, inflammatory and immunological diseases were the most probable etiologies (18 cases, 12.6%), which were diagnosed based on the patients’ past medical history (e.g., Crohn’s disease, tuberculosis) and CT features (no definite space-occupying lesions, mild intestinal wall edema with exudation). Notably, 85 cases (59.4%) in the non-operative group had a clear underlying cause identified during hospitalization.

Table 2.

Etiology and management of small bowel obstruction (SBO) in virgin abdomen

	Immediate surgery	Delayed surgery	Conservative
	n = 124	n = 45	n = 143
Etiology/Suspected dianosis*
Adhesion	34	6	18
Extrernal hernia
Inguinal hernia	5	3	2
Femoral hernia	3	1	2
Umbilical hernia	0	0	1
Lumen-occlusion
Bezoar	12	4	6
Obturator hernia	3		1
Gallstone ileus	10	6	2
Foreign body	1	1	0
Mesenteric ischemia
Arterial	8	2	3
Venous	3	0	0
Internal hernia
Paraduonenal hernia	3	1	8
Transomental hernia	2	0	0
Transmesenteric hernia	1	0	1
Meckel’s diverticulum	3	1	0
Volvulus	12	1	7
Malrotation	0	0	2
Sclerosing encapsulating peritonitis	0	2	0
Inflammatory/Immunologic
Crohn’s disease	1	2	13
Tuberculosis stricture	1	2	2
Intraabdominal abcess	1	2	2
Purpura-related hematoma	1	0	0
Unspecified inflammaiton	1	0	1
Neoplasm
Gastrointestinal stromal tumor	2	2	2
Adenocarcinoma	0	0	1
Metastatic cancer	2	1	5
Lymphoma	2	1	0
Unspecified intra-luminal tumor	1	0	0
Leiomyoma	0	1	0
Ectopic pancreas	0	1	0
Peutz-Jeghers polyp	2	0	0
Hyperplastic adenoma	0	1	0
Inflammatory polyp	2	1	0
Adenomatous polyp	2	0	0
Lipoma	3	2	0
Adenoma	1	0	0
Angiolipoma	0	1	0
Inflammatory myofibroblastic tumor	1	0	0
Negative finding/Unknown diagnosis*	1	0	35
Door-to-operation delay (days)	0.2 ± 0.4 [0, 1]	6.1 ± 4.6 [2, 21]	N/A
Length of hospital stay (days)	10.6 ± 8.2 [1, 82]	17.9 ± 7.4 [7, 43]	7.0 ± 5.1 [0, 43]
Mortality (%)	8(6.5)	4(8.9)	7(4.9)

*For conservative group

Intraoperative findings and short-term outcomes of 169 surgical patients (immediate + delayed surgery) are shown in Table 3. Intraoperative intestinal necrosis was identified in 52 patients (30.8%), and 94 patients (55.6%) underwent enterectomy. The overall postoperative mortality rate was 7.1% (12/169), with the highest mortality observed in patients with volvulus (23.1%, 3/13) and mesenteric ischemia (30.7%, 4/13). The incidence of malignancy in the surgical group was 6.5% (11/169). Further analysis revealed that external hernia (66.7%, 10/15) and volvulus (69.2%, 9/13) had the highest rates of intestinal necrosis, while neoplasms had a relatively low necrosis rate (10.0%, 3/30). These results indicated that adhesions were the leading cause of SBO-VA requiring surgical intervention, while obstruction caused by inflammatory and immunological diseases could mostly be relieved by conservative treatment without surgical intervention.

Table 3.

Etiologies of SBO in surgically-treated patients on the index admission

Etiology	Cases (%)	Necrosis (%)	Enterectomy (%)	Mortality (%)
Adhesion	40(23.7)	13(32.5)	16(40.0)	2(5.0)
Lumen-occlusion	34(20.1)	3(8.8)	4(11.7)	3(8.8)
Bezoar	16	2	3
Gallstone ileus	16	1		3
Foreign body	2		1
Neoplasm	30(17.8)	3(10.0)	28(93.3)	0(0.0)
Gastrointestinal stromal tumor	4		4
Adenocarcinoma	1		1
Metastatic cancer	3		2
Lymphoma	3	1	3
Unspecified intra-luminal tumor	1		1
Leiomyoma	1		1
Ectopic pancreas	1		1
Peutz-Jeghers polyp	2		2
Hyperplastic adenoma	1		1
Inflammatory polyp	3	1	2
Adenomatous polyp	2	1	2
Lipoma	5		5
Adenoma	1		1
Angiolipoma	1		1
Inflammatory myofibroblastic tumor	1		1
External hernia	15(8.9)	10(66.7)	10(66.7)	0(0.0)
Inguinal hernia	8	6	6
Femoral hernia	4	2	2
Obturator hernia	3	2	2
Volvulus	14(7.7)	9(69.2)	9(69.2)	3(23.1)
Mesenteric ischemia	13(7.7)	0	11(84.6)	4(30.7)
Arterial embolism	10	9	9	4
Venous thrombosis	3	2	2
Inflammatory/Immunologic	11(6.5)	1(9.1)	10(90.9)	0(0.0)
Crohn’s disease	3		3
Tuberculosis stricture	3		3
Intraabdominal abscess	3	1	1
Purpura-related hematoma	1		1
Unspecified inflammation	1		1
Internal hernia	7(4.1)	2(28.5)	2(28.5)	0(0.0)
Paraduonenal hernia	4	1	1
Transomental hernia	2
Transmesenteric hernia	1	1	1
Meckel’s diverticulum	4(2.4)	0(0.0)	4(100.0)	0(0.0)
Sclerosing encapsulating peritonitis	2(1.2)	0(0.0)	0(0.0)	0(0.0)
Negative finding	1(0.6)
Total	169	52(30.8)	94(55.6)	12(7.1)

SBO, small bowel obstruction

Short-term and long-term outcomes of the non-operative group are detailed in Table 4. Seven patients (4.9%) died within 30 days of admission, with a mean age of 73.14 ± 20.7 years. Among the deceased patients, 5 had a definite history of Crohn’s disease, and 2 were diagnosed with intra-abdominal metastasis upon admission. The probable etiologies of death included metastatic lung cancer (1 case), volvulus (1 case), arterial ischemia (1 case), uncontrolled Crohn’s disease (2 cases), and adhesions (2 cases). A total of 136 patients achieved obstruction resolution after conservative treatment and were discharged successfully. The median follow-up duration was 37.9 months, with 40 patients lost to follow-up. Recurrence occurred in 32 of the followed-up patients (23.2%), and most recurrences (81.25%, 26/32) happened within 4 years after discharge (Fig. 2). Among the recurrent patients, 15 underwent surgical treatment and 17 received conservative treatment again. The demographic data, medical history, imaging findings, and surgical results of the 15 surgically treated recurrent patients are presented in Supplementary Table S1. Intraoperative etiologies of these 15 recurrent patients were confirmed as gastrointestinal stromal tumor (GIST, 1 case), ileal adenocarcinoma (1 case), lung cancer metastasis (1 case), Crohn’s disease (3 cases), adhesion (3 cases), ileal volvulus (1 case), gallstone ileus (1 case), radiation enteritis (1 case), tuberculosis (1 case), and intra-abdominal abscess (1 case). These results suggest that conservative treatment may mask underlying serious etiologies (e.g., malignancy) in some patients, highlighting the importance of long-term follow-up.

Table 4.

Prognosis of patients with SBO-VA on conservative treatments (n = 143)

Discharged	136
Recurrence	32
Treatments on recurrence
Surgical	15
Conservative	17
Lost to follow-up	40
Deaths (30 days of admission)	7

Fig. 2.

Accumulated recurrence rate of patients with conservatively-treated small bowel obstruction in virgin abdomen

Characteristics of ASBO patients treated with surgery

Given that adhesions were the most common etiology in the surgical group (40 cases, 23.7%), we further analyzed the clinical and radiological features associated with intestinal necrosis in surgical ASBO patients (Table 5). The results showed that ASBO patients with signs of peritonitis (53.8% vs. 11.1%, P = 0.003) and CT findings of mesenteric edema (38.5% vs. 11.1%, P = 0.043) had a significantly higher risk of intraoperative intestinal necrosis. Although the duration of symptoms was shorter in patients with necrosis (2.6 ± 2.0 days vs. 8.2 ± 15.8 days), the difference did not reach statistical significance (P = 0.080). In addition, most adhesions were single adhesive bands (81.5% in non-necrosis group, 100% in necrosis group), predominantly located in the middle and distal segments of the small intestine. There were no significant differences in age, gender, or other symptoms (nausea or vomiting, abdominal pain, distension, obstipation) between the necrosis and non-necrosis groups.

Table 5.

Characteristics of ASBO patients treated with surgery

	Bowel necrosis (n = 40)		p value
	No (n = 27) (%)	Yes (n = 13) (%)
Age (years)	60.9 ± 16.5	58.6 ± 13.2	0.673
Male	15(55.6)	6(46.2)	0.577
Duration of symptoms (days)	8.2 ± 15.8	2.6 ± 2.0	0.080
Symptoms
Nausea/vomiting	16(59.3)	5(38.5)	0.217
Abdominal pain	22(81.5)	13(100)	0.154
Distension	13(48.1)	5(38.5)	0.564
Obstipation	14(51.9)	9(69.2)	0.298
History of prior episodes	4(14.8)	1(7.7)	1
Signs
Temperature (Celsius)	36.7 ± 0.3	36.9 ± 0.7	0.408
Tachycardia	5(18.5)	4(30.8)	0.385
Peritonitis sign	3(11.1)	7(53.8)	0.003*
Computerized tomography findings
Ascites	10(37.0)	7(53.8)	0.314
Closed loop	2(7.4)	4(30.8)	0.075
Small bowel feces sign	3(11.1)	2(15.4)	1
Swirl sign	2(7.4)	1(7.7)	1
Bowel thickening/enhancement	4(14.8)	3(23.1)	0.662
Mesenteric edema	3(11.1)	5(38.5)	0.043*
Mass	2(7.4)	0(0.0)	1
Pneumatosis intestinalis	0(0.0)	1(7.7)	0.325
Transition point	12(44.4)	3(23.1)	0.191
Location of obstruction
Jejunum	2(7.4)	1(7.7)	0.321
Middle	4(14.8)	3(23.1)
Ileum	18(66.7)	5(38.5)
Unspecified	3(11.1)	4(30.8)
Type of adhesion
Single band	22(81.5)	13(100)	0.154
Extensive matted	5(18.5)	0(0)
Length of hospital stay(days)	12.7 ± 7.7	10.0 ± 4.3	0.240
Enterectomy	3(11.1)	13(100)	0.000*
Mortality	1(4.2)	1(6.3)	1

ASBO, adhesive small bowel obstruction; *, p value <0.05

Diagnostic role of CT abdomen scan

Among 169 surgical patients, 148 underwent preoperative abdominal CT examination. The comparison between CT diagnosis and intraoperative findings is shown in Table 6. The results demonstrated that the overall consistency rate between CT diagnosis and final intraoperative etiology was 60.14% (89/148). CT had the highest positive predictive value for obturator hernia, paraduodenal hernia, gallstone ileus, bezoar, arterial ischemia, and venous thrombosis (all 100%), followed by intussusception (92.6%). However, the PPV of CT for volvulus (57.1%), adhesion (60.0%), and neoplasm (57.1%) was relatively low. Notably, 34 patients were diagnosed with “SBO confirmed, no underlying cause identified” by CT, but intraoperative findings revealed definite etiologies in 33 cases (97.1%), mainly including adhesion (14 cases), bezoar (5 cases), and volvulus (3 cases).

Table 6.

Correlation between CT diagnosis and laparotomy findings

CT-abdomen diagnosis (n)	Findings at laparotomy (n)	CT-abdomen diagnosis		CT positive predictive value (%)
		Inaccurate or missed	Correct
Underlying cause suggested (n = 102)
Inguinal hernia (7)	Inguinal hernia (5)		5	71.4
	Femoral hernia (1)	1
	Arterial embolism (1)	1
Femoral hernia (4)	Femoral hernia (3)		3	75.0
	Arterial ischemia (1)	1
Obturator hernia (3)	Obturator hernia (3)		3	100.0
Paraduodenal hernia (2)	Paraduodenal hernia (2)		2	100.0
Internal hernia, unspecified (5)	Adhesion, band (2)	2		40.0
	Volvulus (1)	1
	Transomental hernia (1)		1
	Paraduodenal hernia (1)		1
Gallstone ileus (16)	Gallstone ileus (16)		16	100.0
Bezoar (4)	Bezoar (4)		4	100.0
Arterial ischemia (3)	Arterial ischemia (3)		3	100.0
Venous thrombosis (1)	Venous thrombosis (1)		1	100.0
Intussception(27)	Intussception (25)		25	92.6
	Bezoar (1)	1
	Foreign body (1)	1
Volvulus (7)	Volvulus (4)		4	57.1
	Adhesion, band (2), unspecified(1)	3
Malrotation (1)	Paraduodenal hernia (1)	1		0.0
Inflammatory bowel disease (3)	Crohn’s disease (2)		2	66.7
	Arterial ischemia (1)	1
Adhesion, band (7)	Adhesion, band (7)		7	100.0
Adhesion, unspecified (5)	Adhesion, dense (2)		2	60.0
	Adhesion, band (1)		1
	Meckel’s diverticulum (1)	1
	Arterial ischemia (1)	1
Neoplasm (7)	Gastrointestinal stromal tumor (2)		2	57.1
	Lymphoma (1)		1
	Leiomyoma (1)		1
	Bezoar (1)	1
	Tuberculosis stricture (1)	1
	Inguinal hernia (1)	1
Only signs of strangulation (n = 11)
Close-loop (3)	Adhesion, band (2)	2		0.0
	Volvulus (1)		1
Bowel wall thickening (7)	Crohn’s disease (1)		1
	Venous thrombosis (2)		2
	Appendiceal abscess (1)	1
	Tuberculosis stricture (1)	1
	Transmesenteric hernia (1)	1
	Unspecified intestinal inflammation (1)		1
Pneumatosis intestinalis (1)	Volvulus (1)	1
SBO confirmed, no underlying cause identified (34)	Adhesion, band (9)	9		0.0
	Adhesion, unspecified (5)	5
	Inguinal hernia (1)	1
	Bezoar (5)	5
	Foreing body (1)	1
	Arterial ischemia (2)	2
	Transomental hernia (1)	1
	Meckel’s diverticulum (2)	2
	Volvulus (3)	3
	Sclerosing encapsulating peritonitis (2)	2
	Tuberculosis stricture (1)	1
	Intra-abdominal abscess (1)	1
	Negative finding (1)	1
Other - Pancreatis (1)	Bezoar (1)	1		0.0
Total	n = 148	39.86%	60.14%

The correlation between CT features and intestinal necrosis in surgical patients is presented in Table 7. The results showed that ascites (63.6% vs. 36.5%, P = 0.002), closed loop (22.7% vs. 7.7%, P = 0.011), bowel thickening/attenuation (27.3% vs. 13.5%, P = 0.044), mesenteric edema (25.0% vs. 8.7%, P = 0.008), pneumatosis intestinalis (4.5% vs. 0.0%, P = 0.029), and absence of intussusception (4.5% vs. 25.0%, P = 0.004) and neoplasm (0.0% vs. 11.5%, P = 0.019) were significantly associated with intestinal necrosis. These CT features can serve as important indicators for predicting intestinal necrosis and guiding surgical decision-making.

Table 7.

CT features of the patient with necrotic intestine during the surgery (n = 148)

CT features	Necrosis		p value
	No (n = 104) (%)	Yes (n = 44) (%)
Ascites	38(36.5)	28(63.6)	0.002*
Transition point found	53(51.0)	23(52.3)	0.884
Closed loop	8(7.7)	10(22.7)	0.011*
Small bowel feces sign	8(7.7)	8(18.2)	0.060
Swirl sign	5(4.8)	2(4.5)	1.000
Bowel thickening/attenuation	14(13.5)	12(27.3)	0.044*
Mesenteric edema	9(8.7)	11(25.0)	0.008*
Intussception	26(25.0)	2(4.5)	0.004*
Bezoar impaction	24(23.1)	2(4.5)	0.007*
Pneumatosis intestinalis	0(0.0)	2(4.5)	0.029*
Neoplasm	12(11.5)	0(0.0)	0.019*

*, p value <0.05

Complete CT data were available in 126 of 143 non-operative patients, and their CT features are presented in Supplementary Table S2. The most common CT features were ascites (57 cases, 45.2%), transition point found (51 cases, 40.5%), and bowel thickening/attenuation (37 cases, 29.4%). The CT diagnosis results of the non-operative group are shown in Supplementary Table S3, with 85 cases (67.5%) having an underlying cause suggested and 41 cases (32.5%) having no clear cause identified. Supplementary Table S4 shows the etiologies of patients with intussusception on CT (n = 25), including lipoma (5 cases), inflammatory polyp (3 cases), adenomatous polyp (2 cases), and metastatic cancer (2 cases) et al. Among patients with CT findings suggesting neoplasms, 25 out of 30 cases (83.3%) presented as intussusception, and the remaining 5 cases showed definite space-occupying lesions on CT, indicating potential malignancy (including 2 cases of GIST, 2 cases of lymphoma, and 1 case of leiomyoma). In addition, among patients who achieved successful conservative treatment, 32 cases showed CT features of “no definite etiology (e.g., space-occupying lesion, volvulus, internal hernia) and presence of transition zone”. Combined with their clinical features of no malignant history and elevated inflammatory indicators, it was speculated that the obstruction in these patients was mostly caused by adhesions or inflammatory bowel disease, indicating that they were suitable candidates for conservative treatment.

Given the extended study period (2009–2020) spanning an era of significant advancements in CT technology, we analyzed temporal trends in diagnostic approaches and their success in establishing a definitive etiology within the conservatively managed cohort (n = 143). When comparing the earlier (2009–2014, n = 68) and later (2015–2020, n = 75) periods, a clear shift in practice was evident. The utilization of CT as the primary imaging modality increased substantially, from 79.4% (54/68) of patients in the earlier period to 96.0% (72/75) in the later period (p < 0.001). However, this near-universal adoption of modern CT did not translate into a higher rate of definitive diagnosis. Among patients who underwent CT, the proportion in whom no definitive etiology could be inferred from imaging and clinical data showed a non-significant numerical increase, from 18.5% (10/54) in 2009–2014 to 34.7% (25/72) in 2015–2020 (p = 0.056). This trend underscores that the challenge of achieving a conclusive diagnosis in non-operatively managed SBO-VA persists despite technological improvements in imaging.

Discussion

The approach to managing SBO has evolved to favor selective nonoperative strategies, particularly for obstruction caused by postoperative adhesions [15, 16]. However, the optimal management for SBO-VA is still debated. A traditional, more aggressive surgical stance persists in some centers, driven by the concern that the absence of prior surgery implies a higher likelihood of strangulating obstruction or occult malignancy [9]. This viewpoint is challenged by contemporary consensus. A 2021 position paper by the World Society of Emergency Surgery (WSES) concluded that the etiology and outcomes of SBO-VA are comparable to those in patients with prior surgery, and therefore recommend that SBO-VA be managed according to the same risk-stratified guidelines [10]. Data from our large Chinese cohort supports this modern perspective, demonstrating that a tailored approach is necessary and that a significant number of patients can be managed successfully without immediate surgery.

A critical step in managing SBO-VA is understanding its diverse etiology, as this directly informs treatment decisions and prognosis [17]. Our findings confirm and elaborate upon the etiological distribution reported previously. Adhesions were the single most common cause, despite the absence of prior surgery. This aligns with other studies indicating that de-novo adhesions from subclinical inflammation are a significant entity [8, 9] and is consistent with the WSES review, which identified adhesions as the cause in roughly half of SBO-VA cases [10].

Following adhesions, luminal obstructions (e.g., bezoars) and neoplasms were the next most frequent causes in our cohort. Our data reveals distinct epidemiological characteristics compared to some Western cohorts. The proportion of luminal occlusions (20.1%) was substantial, likely attributable to dietary factors such as high-fiber diets predisposing to phytobezoar formation, a finding supported by other studies [18, 19]. Benign neoplasms represented a higher proportion of tumors than often anticipated. The overall malignancy rate was 4.5%, and importantly, many neoplasms presented with features—such as intussusception for benign lesions or a discernible mass on imaging—that could raise preoperative suspicion. This etiological profile has direct clinical relevance. The historical rationale for mandatory exploration often cited the high risk of missing a malignancy [20]. Our data, supported by literature indicating most small bowel tumors are benign [21–24], suggests this risk can be mitigated by careful imaging. The ability to suspect a malignant or benign process preoperatively allows for more selective surgical planning, avoiding unnecessary emergency laparotomies where a trial of conservative management is safe.

The operative rate in our SBO-VA cohort was 54.1%, comparable to the 50–60% rates reported elsewhere [8, 20], indicating nearly half of all patients were managed initially without surgery. This aligns with the WSES report, which notes that nonoperative management is often successful when attempted [10]. Our observed mortality rates (7.1% surgical, 4.6% conservative) were higher than some series, likely explained by our tertiary referral center receiving more complex, transferred cases. Patients with volvulus and mesenteric ischemia had the poorest outcomes, underscoring the need for timely intervention in these subsets.

Analysis clarifies which patients benefit most from surgery. Conditions with a high risk of strangulation or ischemia—volvulus, adhesive bands with confirmed necrosis, strangulated hernias, and mesenteric ischemia—unquestionably require operative management. Identifying these high-risk cases is a key principle of the risk-stratified approach endorsed by current guidelines [10]. For other etiologies, like uncomplicated luminal obstructions or some benign neoplasms, a nonoperative approach is often viable. Studies show the success rate of conservative management can exceed 80%, especially with WSCA [19, 20]. Although our study did not routinely use WSCA, its established efficacy suggests that a structured protocol could safely reduce the operative rate for stable patients.

CT is the cornerstone of SBO evaluation [25, 26]. Multidetector CT (MDCT) improves diagnostic accuracy for determining etiology and severity [27, 28] and is crucial for risk stratification. CT reliably identifies “danger signs” that predict the need for surgery: closed-loop obstruction, mesenteric edema, pneumatosis, portal gas, and significant ascites [27, 29, 30]. Their presence should lower the threshold for surgery. Conversely, their absence supports a trial of conservative management. Although adhesions are not directly seen, a transition point without another clear cause is highly predictive of adhesive obstruction [25, 31, 32]. Our study adds a practical insight. Among surgical adhesive SBO-VA patients, the bowel necrosis rate was 32.5%. Those with peritonitis or CT evidence of mesenteric edema were more likely to have necrosis. This reinforces that combining clinical exam and CT findings provides objective criteria for identifying adhesive obstructions needing early surgery.

The successful resolution of SBO with conservative treatment, while clinically reassuring, does not confer a definitive diagnosis. In our cohort, 59.4% of non-operatively managed patients were discharged without a clear etiology, a finding that underscores the inherent diagnostic ambiguity in such cases. More critically, the operative findings in patients who presented with recurrence revealed a spectrum of significant pathologies, including neoplasms (e.g., GIST, adenocarcinoma) and Crohn’s disease. This data directly challenges the common assumption that a resolved obstruction equates to “benign adhesive disease”. Consequently, attributing the cause solely to adhesions after successful non-operative management carries a risk of missing underlying, and sometimes serious, conditions. These findings highlight the necessity for a more vigilant and structured diagnostic follow-up protocol for patients with SBO-VA who are initially managed conservatively, particularly those who experience recurrence.

Furthermore, our data quantify the specific risk of missed malignancy. Only 3 of 143 conservatively managed patients (2.1%) were later found to have cancer. The time from initial discharge to surgical diagnosis was short (2 weeks to 3 months), and no clear evidence suggested these delays altered ultimate treatment outcomes. However, these cases underscore that a successful conservative episode does not rule out cancer. Therefore, we recommend clear communication of this low risk, scheduled early follow-up (e.g., within 1–3 months), and prompt re-evaluation for any recurrent symptoms, even after initial success.

Our study provides a realistic assessment of CT’s diagnostic capabilities in SBO-VA. While CT is indispensable for identifying high-risk features of strangulation (e.g., closed-loop, mesenteric edema) and guiding urgent surgical decisions, its ability to pinpoint the precise etiology is more limited, as evidenced by the 60.1% concordance rate with surgical findings. This moderate accuracy, especially for common causes like adhesions and neoplasms, illuminates a key clinical dilemma: CT is highly reliable for deciding when to operate but less so for determining why the obstruction occurred. This diagnostic limitation directly contributes to the uncertainty in post-conservative management diagnosis. Therefore, a CT scan that does not reveal a specific cause should not be interpreted as definitively ruling out significant pathology. This reinforces the need for integrating clinical judgment and considering further diagnostic evaluation in the long-term management of these patients.

Several limitations of our study must be acknowledged. Its retrospective nature may introduce bias in treatment selection. The extended study period (2009–2020) was necessary to assemble a sufficient cohort of this relatively uncommon condition, but this may raise questions about the current applicability of the findings. Importantly, the core principles emerging from our work, align with the conclusions of more recent studies [33], supporting their continued relevance. Furthermore, the diagnostic accuracy of CT in our cohort was moderate (60.14%), underscoring that pinpointing the exact cause without surgery remains a challenge and an area for future improvement. Finally, a significant number of patients in the conservatively managed group were lost to follow-up, which may affect the precision of our long-term recurrence analysis.

SBO in the virgin abdomen is a heterogeneous entity. Adhesions, luminal obstructions, and neoplasms are predominant causes, with epidemiological variations across populations. The traditional mandate for routine surgical exploration is not justified. Instead, a risk-stratified, individualized management algorithm is essential. This should integrate serial clinical assessments with targeted CT imaging to identify high-risk features of strangulation or ischemia. For patients without these signs, a trial of conservative management, ideally augmented with water-soluble contrast, is a safe and effective first-line strategy, with readiness to convert to surgery if needed. Future prospective studies with standardized protocols for WSCA use are needed to optimize this approach.

Supplementary Information

Below is the link to the electronic supplementary material.

Abbreviations

SBO

Small bowel obstruction

VA

Virgin abdomen

SBO-VA

Small bowel obstruction in a virgin abdomen

ASBO

Adhesive small bowel obstruction

CT

Computed tomography

MDCT

Multi-detector computed tomography

WSCA

Water-soluble contrast agent

GIST

Gastrointestinal stromal tumor

IRB

Institutional review board

STROCSS

Strengthening the reporting of cohort, cross-sectional and case-control studies in surgery

IQR

Interquartile range

SD

Standard deviation

NPV

Negative predictive value

PPV

Positive predictive value

AUC

Area under the curve

LOS

Length of stay

Author contributions

QYW and ZYH collected and analyzed the patient data, and were equally contributor in writing the manuscript. PXC degined this study and interpreted the patient data. All authors read and approved the final manuscript.

Funding

This study was supported by the National Natural Science Foundation of China [No. 81802442]. The funder had no role in the design, data collection, data analysis, or reporting of this study.

Data availability

All data generated or analysed during this study are included in this published article and its supplementary information files.

Declarations

Ethics approval and consent to participate

The study was ethically approved and patients informed consent from the retrospective patient cohort was waived by the Medical Ethics Committee of the First Affiliated Hospital of Nanjing Medical University [No. 2023-SR-340].

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.