Rapid, intense pericholedochal fibrosis after preoperative biliary drainage: A prospective histologic study in pancreatoduodenectomy specimens
1Department of General Surgery, Rambam Health Care Campus, Haifa, Israel
2The Ruth and Bruce Rappaport Faculty of Medicine, Technion Institute of Technology, Haifa, Israel
3The Institute of Pathology, Rambam Health Care Campus, Haifa, Israel
Corresponding author: Offir Ben-Ishay, MD, FACS Department of General Surgery, Rambam Health Care Campus, 8 HaAliyah St., Haifa 31096, Israel Tel: +972-4-8541730, Fax: +972-4-8542321, E-mail: o_ben-ishay@RMC.gov.il ORCID: https://orcid.org/0000-0003-3603-3843Abstract
Backgrounds/Aims
Preoperative biliary drainage (PBD) is commonly used prior to pancreatoduodenectomy (PD), but its histologic effects on the extrahepatic bile duct are not well understood in humans. This study aimed to prospectively measure pericholedochal fibrosis (PCF) in PD specimens after plastic biliary stenting to assess its extent and clinical significance.
Methods
Consecutive patients undergoing PD were divided into two groups: those who received PBD (n = 22) and non-drained controls (n = 24). Patients who had neoadjuvant chemotherapy were excluded to focus on stent-related effects. Common bile duct (CBD) specimens were analyzed using standardized Masson’s trichrome staining. Digital morphometry quantified CBD dimensions, collagen area, and collagen density. Histologic markers were correlated with stent dwell time and surgical outcomes.
Results
PBD was linked to a substantial increase in PCF. Stented ducts showed significantly greater wall thickness (6,554 vs. 499 µm; p < 0.001), total collagen area (p < 0.001), and collagen density (p < 0.001) compared to controls. Fibrosis developed rapidly, becoming clearly evident by day 6, with no significant correlation between collagen burden and stent dwell time (median 10 days). Despite these pronounced histologic changes, operative time (230 vs. 230 minutes; p = 0.98) and postoperative complication rates did not differ significantly between the groups.
Conclusions
Short-term PBD with plastic stents causes rapid, intense, and persistent PCF that stabilizes soon after stent placement. Although this fibrotic response did not negatively impact surgical outcomes at a high-volume center, the findings underscore the significant tissue remodeling triggered by stenting and advocate for the careful use of PBD.
INTRODUCTION
Adenocarcinoma of the pancreatic head represents the majority of exocrine pancreatic tumors, with only 15%–20% of patients presenting with resectable disease [1-3]. Because the common bile duct (CBD) traverses the pancreatic head, obstructive jaundice is observed in up to two-thirds of patients at diagnosis [1-3].
Historically, operating on jaundiced patients was considered high risk, leading to the widespread use of preoperative biliary drainage (PBD). However, randomized trials and meta-analyses have called this practice into question, revealing increased rates of cholangitis, pancreatic fistula, and prolonged hospital stays among drained patients [4-18]. Nonetheless, PBD remains necessary for selected patients, particularly those with acute cholangitis, severe hyperbilirubinemia, significant comorbidities that preclude early surgery, or those requiring neoadjuvant chemotherapy.
While the clinical outcomes of PBD have been extensively documented, little is known about its histologic impact on the extrahepatic bile duct and surrounding tissues in humans [19-24]. Animal studies and limited human case reports suggest that biliary plastic stents can trigger bacterial colonization, chronic inflammation, and fibro-proliferative changes, which may complicate surgical dissection [19-24]. Similarly, prospective case series have reported increased fibrosis and tissue reactions around stented ducts, although quantitative morphometric data in humans remain limited.
It is unclear whether these observations translate into quantifiable fibrosis in human pancreatoduodenectomy (PD) specimens and whether such fibrosis correlates with operative difficulty or morbidity. This study prospectively evaluated pericholedochal fibrosis (PCF) in CBD segments from PD specimens in patients with and without PBD, utilizing standardized trichrome staining and digital morphometry. We also explored associations with operative and postoperative outcomes, aiming to clarify the tissue-level impact of biliary stenting and its clinical relevance in the hands of experienced surgeons. Understanding the tissue-level consequences of PBD is directly relevant to hepatopancreatobiliary surgeons and endoscopists when selecting drainage strategies and determining the timing of PD.
MATERIALS AND METHODS
Study design and patient cohort
Patients were selected from a previously described institutional PD database, which was stratified by PBD status. For this histologic study, consecutive eligible patients undergoing PD for pancreatic head adenocarcinoma were enrolled. Inclusion required the availability of CBD tissue for standardized histologic processing. PBD was performed via endoscopic retrograde cholangiopancreatography (ERCP) with plastic biliary stent placement, based on clinical indications. Patients receiving neoadjuvant chemotherapy were excluded to isolate the inflammatory effect of the stent itself. Clinical variables, operative details, and postoperative outcomes were collected retrospectively from medical records. The study was approved by Rambam Health Care Campus institutional review board in Haifa, Israel (058-14-RMB).
Histologic sampling and staining
At PD, the extrahepatic CBD was routinely identified, sectioned at a standardized level approximately 1 cm distal to the hepatic confluence, and submitted entirely for histologic evaluation. All slides for this study were prepared prospectively following a uniform protocol and stained with Masson’s trichrome to differentiate mature collagen (stained blue) in the pericholedochal region from other tissue components.
To investigate whether the degree of fibrosis increased with stent dwell time, a correlation analysis was conducted between the interval from PBD to surgery and quantitative collagen indices (collagen area, collagen area as a percentage of CBD area, and mean collagen gray level). Pearson’s correlation coefficient (or Spearman’s, if non-normal) was calculated for patients in the PBD group only.
Pathologic evaluation and morphometric analysis
A senior gastrointestinal pathologist with > 15 years of experience evaluated all slides, focusing on duct architecture, wall integrity, and the degree of fibrosis. For quantitative analysis, high-resolution images were digitized using a calibrated color camera (Retiga 2000, Q-Imaging) and processed with Image Pro Plus (v6.3, Media Cybernetics, Inc.).
Calibrated measurements included: (1) CBD area, (2) wall width/thickness, (3) perimeter, (4) maximum diameter, and (5) maximum radius. All measurements were converted from pixels to micrometers (µm) or square micrometers (µm2) based on system calibration. The collagen area was defined as the blue-stained pericholedochal fibrous tissue surrounding the muscular wall of the CBD and was expressed in µm2.
In addition to the absolute collagen area, a normalized measure of fibrotic burden was calculated as the percentage of the CBD cross-sectional area occupied by collagen (collagen area / CBD area × 100), referred to as the collagen fraction. To account for potential confounding factors such as age and sex, multivariable linear regression models were constructed with collagen fraction and collagen area as dependent variables, using PBD status (yes/no) as the main predictor while adjusting for age and sex.
Collagen density was quantified as integrated optical density (IOD), calculated by multiplying the mean gray level (pixel intensity on a scale of 0–255) by the collagen area in µm2. Higher IOD values indicate increased collagen quantity as well as greater density, maturity, and compactness. Gray level measurements were recorded for overall intensity and for individual color channels (red, green) to ensure a consistent assessment of blue-stained collagen.
Clinical data collection
All PBD procedures were performed by a senior gastroenterologist using ERCP. Routine prophylaxis included either ceftriaxone 1 g IV or ciprofloxacin 500 mg per os. An endoscopic papillotomy was routinely performed, followed by the placement of a 7-French Advanix biliary stent (Boston Scientific). Successful drainage was defined as a reduction in serum bilirubin levels of at least 30%–50% within 48 hours following the intervention. Only patients with successful primary drainage were included in the PBD group.
Clinical data abstracted from the medical records included age, sex, comorbidities (smoking history, diabetes mellitus, chronic pancreatitis), preoperative bilirubin levels, and the interval from stent placement to operation.
Surgical and postoperative outcomes
Operative variables included operative time (skin-to-skin), estimated blood loss, and the need for transfusion. Intraoperative complications (vascular injury, major organ injury) were recorded. Postoperative complications were classified according to the Clavien-Dindo system and included surgical site infection (SSI), intra-abdominal abscess, pancreatic fistula (grade B or C), bile leak, venous thromboembolism, and pneumonia. Mortality was tracked for up to 90 days after surgery.
Oncologic outcomes assessed included the number of lymph nodes harvested, R0 versus R1 resection status, and overall survival duration from the date of surgery.
Statistical analysis
Continuous variables with a normal distribution were compared using Student’s t-test, while non-normally distributed variables were analyzed using the Mann-Whitney U test. Categorical variables were compared using the chi-square test or Fisher’s exact test, as appropriate. To reduce type I error from multiple morphometric comparisons, CBD wall thickness, collagen area, and collagen IOD were pre-specified as primary histologic outcomes and were the focus of statistical testing.
Multivariable linear regression was employed to explore associations between PBD status and the primary histologic outcomes (collagen area and IOD), adjusting for age and sex as potential confounders.
For clinical outcomes (operative time, complications, mortality), data are presented descriptively to acknowledge the limited sample size and the underpowered design for these secondary endpoints.
A two-sided p-value < 0.05 was considered statistically significant. Analyses were performed using JMP Pro version 15.0.0 (SAS Institute).
RESULTS
Baseline patient characteristics
Twenty-two patients underwent PBD before PD (study group), while 24 patients proceeded directly to surgery without drainage (control group). The PBD group comprised more men (81.8% vs. 33.3%, p < 0.001) and had a higher median preoperative serum bilirubin level (12.8 mg/dL vs. 7.2 mg/dL, p = 0.03), indicating clinical selection for drainage in more severely jaundiced patients. Other demographic factors, including age and comorbidities such as smoking, diabetes mellitus, and chronic pancreatitis, did not differ significantly between the groups.
All patients in the PBD group presented with jaundice; notably, 60% of the control patients also had hyperbilirubinemia but proceeded directly to surgery. This reflects institutional practice and surgeon preference for selected lower-risk patients.
Primary histologic findings
Prospective morphometric analysis demonstrated significantly more pronounced PCF in stented patients compared to controls (Fig. 1). CBD wall thickness was markedly increased in the study group (6.554 ± 3.968 pixels vs. 4.99 ± 1.11 pixels, p < 0.001). Collagen area, the primary measure of fibrotic burden, was substantially higher in PBD patients (25,315,550 ± 21,865,237 pixels vs. 112,667 ± 77,843 pixels, p < 0.001). In addition, stented ducts demonstrated significantly larger area, maximum diameter, and perimeter, consistent with chronic dilation and wall remodeling in response to sustained inflammation and fibrosis (Table 1, all p < 0.001). Collagen density, assessed by IOD, was significantly elevated in the study group, with higher gray levels (minimum, maximum, and individual color channels) indicating denser, more intensely stained collagen (Table 2, all p ≤ 0.03).
When collagen deposition was expressed as a fraction of the CBD cross-sectional area, patients with PBD demonstrated a higher fibrotic burden. The joint distribution of collagen quantity and density by group is shown in Fig. 2C, where PBD cases cluster at markedly higher collagen areas, while controls remain at low collagen levels with overlapping mean gray values. The mean collagen fraction was 57.7% ± 20.3% in the PBD group (n = 22) compared to 51.3% ± 22.2% in controls (n = 24; p = 0.31). Although this difference did not reach statistical significance, it is directionally consistent with the markedly higher absolute collagen area in the PBD group (25,315,551 ± 21,865,238 µm2 vs. 112,668 ± 77,844 µm2; p < 0.001).
Mean collagen gray level within the collagen mask (glmncol) was similar between groups (144.6 ± 21.4 in PBD vs. 142.0 ± 26.2 in controls; p = 0.71). This suggests that the primary histologic effect of PBD is an increase in collagen quantity rather than a significant change in average staining intensity.
In multivariable linear regression models that adjusted for age and sex, PBD status remained strongly and independently associated with increased absolute collagen area (b = 2.41 × 107; p < 0.001) and IOD (b = 3.56 × 109; p < 0.001). Additionally, PBD was an independent predictor of increased bile duct wall thickness (b = 6,006.7 mm; p < 0.001). In contrast, the association with collagen fraction (as a percentage of CBD area) was not statistically significant in the multivariable model (p = 0.800). This suggests that while stenting increases total collagen quantity and wall size, the relative proportions of the expanded tissue components are more complexly distributed.
Time from stenting to surgery and fibrosis
Among PBD patients, the median interval from stent placement to PD was 10 days (range: 5–78 days). The collagen area showed no correlation with stent dwell time (r = 0.01, p = 0.95), and the mean collagen gray level was similarly uncorrelated (r = −0.05, p = 0.84). The collagen fraction exhibited only a weak, non-significant positive correlation with dwell time (r = 0.34, p = 0.14). These relationships are illustrated in Fig. 2A and 2B and indicate that, within the observed 5–78-day window, the intense PCF induced by PBD is established early and does not measurably increase with longer short-term drainage.
Time course of pericholedochal fibrosis
The median interval between stent placement and PD was 10 days (range 5–78 days). Robust PCF was already evident in specimens collected 6 days post-stenting, characterized by substantial collagen deposition and wall thickening. Specimens obtained at 8, 10, 12, 19, and 24 days post-stenting exhibited continued or equivalent fibrosis, with no clear statistical trend indicating further increases in collagen area or IOD with prolonged stent duration (Fig. 3). This pattern suggests that the fibrotic response is established rapidly (by day 6) and then plateaus, rather than accumulating linearly over the following weeks.
Exploratory clinical outcomes
Despite the presence of intense and established local PCF, operative outcomes did not differ significantly between the groups. The operative times were nearly identical, with 230 ± 50.8 minutes in the PBD group compared to 229.8 ± 58.9 minutes in the control group (p = 0.98). This suggests that the fibrosis did not measurably hinder surgical dissection or prolong operative duration among this cohort of experienced surgeons. Estimated intraoperative blood loss and the need for transfusion were similar between the groups.
Postoperative complication rates, stratified by Clavien-Dindo grade, showed no statistically significant differences (p = 0.42, Table 3). Specific complications, including SSIs, intra-abdominal abscesses, pancreatic fistulas, venous thromboembolism, and pneumonia, occurred at comparable frequencies. Mortality was observed in 2 patients (9.1%) in the PBD group and 3 patients (12.5%) in the control group (p = 0.71), a difference that was not statistically significant.
However, the confidence intervals around these clinical endpoints are wide, reflecting the limited sample size. The study was sufficiently powered to detect the large histologic differences observed (p < 0.001) but remains underpowered to identify modest differences in operative time or complication rates.
Oncologic outcomes
Oncologic adequacy was comparable between groups. The median number of lymph nodes harvested was similar (15.0 ± 3.8 in the PBD group vs. 15.6 ± 5.2 in controls, p = 0.62). R1 resection rates (microscopically positive margins) were 18.2% in the PBD group and 8.3% in controls (p = 0.32). Median overall survival was 13.5 months in the PBD group and 15.0 months in controls (p = 0.77), with no statistically significant difference.
DISCUSSION
This prospective clinico-pathologic study demonstrates that PBD using plastic stents leads to rapid and significant PCF in human extrahepatic bile ducts. The stented ducts were significantly larger, had markedly thicker walls, and contained substantially more and denser collagen compared to non-stented controls. This findings corroborate and quantify previous qualitative observations and animal data [19-24]. This study provides the first systematic quantitative evidence in humans regarding the extent and density of collagen deposition associated with short-term plastic biliary stenting.
Wagholikar et al. [21] previously reported morphological changes in bile ducts following preoperative biliary stenting in humans, noting mural edema, inflammation, and fibro-proliferative thickening that were believed to complicate surgical procedures. However, their assessment was primarily qualitative and relied on routine histology without standardized morphometry. In contrast, the present study confirms and expands upon those findings by quantitatively demonstrating that plastic stents are linked to a dramatic increase in pericholedochal collagen area and density when compared to non-stented controls. Furthermore, it shows that in a high-volume center, this intense fibrosis does not result in longer operative times or significantly higher complication rates.
Biological impact and mechanism of fibrosis
Fibrosis was well-established within 6 days of stent placement, with no significant increase by 24 days, suggesting that the tissue response is both rapid and robust. This early and plateau pattern aligns with acute mechanical irritation and bacterial colonization from the stent, triggering an initial acute inflammatory cascade that quickly transitions to fibro-proliferative remodeling, with mature collagen being deposited and stabilized within the first week [19-24].
The density and intensity of collagen, as reflected in IOD measurements, parallel its abundance. This indicates that stenting not only increases collagen quantity but also promotes the deposition of compact, mature collagen fibers instead of loose edematous tissue. This may reflect the high metabolic activity of fibroblasts and myofibroblasts activated in response to the chronic stimulus of the indwelling stent.
By incorporating collagen fraction as a normalized metric, this study demonstrates that PBD not only enlarges the CBD but also replaces a significantly greater proportion of the duct wall with dense collagen. The absence of a clear relationship between stent dwell time and fibrotic indices within the 5–24-day window suggests a threshold effect, with rapid saturation of the fibrotic response occurring soon after stent placement. These observations reinforce the biological impact of even short-term plastic stenting and support the need for early surgery once drainage has achieved its immediate clinical goals.
Our multivariable analysis shows that the observed fibrosis is not merely a byproduct of severe jaundice or patient age. Even after adjusting for these factors, stented ducts exhibited a substantial increase in collagen deposition (Fig. 4). Notably, 60% of our control patients also presented with hyperbilirubinemia but did not develop the intense PCF observed in the PBD group, further supporting the role of mechanical and inflammatory stent-induced injury as the primary driver of these changes.
Clinical correlation and interpretation of negative operative findings
Interestingly, the pronounced PCF did not result in measurable increases in operative difficulty or morbidity in this cohort, where pancreatoduodenectomies were performed by experienced pancreatic surgeons at a high-volume institution. Operative times were nearly identical between the groups, and there were no significant differences in complication rates or mortality.
These negative clinical findings should be interpreted with caution. The study was designed to detect large histologic differences (p < 0.001) but was not powered to identify modest differences in complications, and the confidence intervals around operative outcomes remain wide. Nevertheless, the absence of increased operative time or major complications is reassuring. It suggests that, in the hands of skilled surgeons, proficient dissection can typically overcome the local fibrotic reaction induced by short-term PBD. Despite the significant histologic changes, operative metrics at a high-volume center were not adversely impacted. This indicates that the biological reality of fibrosis does not necessarily dictate clinical operative failure in expert hands.
Study design and scope: plastic stents and short-term drainage
We intentionally excluded patients receiving neoadjuvant chemotherapy to focus on the inflammatory effects of the biliary stent alone, avoiding the confounding influence of systemic cytotoxic drugs that can worsen local fibrosis. By establishing a baseline of pure stent-induced injury in chemotherapy-naïve patients, our findings serve as a reference point for comparing the more complex scenarios associated with modern neoadjuvant protocols.
It is important to note that this study only assessed plastic stents over relatively short dwell times (median 10 days). In current practice, many high-volume centers now favor self-expanding metal stents (SEMS) for patients needing longer-term drainage (e.g., neoadjuvant therapy lasting weeks to months), as SEMS are associated with lower rates of stent occlusion and may present different risk-benefit profiles. While SEMS are commonly used, plastic stents remain prevalent for short-term bridging or in resource-limited settings. Additionally, this study establishes a baseline of ‘pure’ mechanical injury without the confounding effects of thermal expansion associated with SEMS. Future research should investigate whether the rapid fibrotic response varies with different stent technologies or durations.
Clinical implications for endoscopy and surgery
The rapid onset and intensity of PCF documented here underscore the principle that PBD should be reserved for patients with clear clinical indications (active cholangitis, severe comorbidity, planned neoadjuvant therapy) and avoided in those who can proceed promptly to surgery. Even short-term stenting induces permanent tissue remodeling, which, while manageable by expert surgeons, still poses an unnecessary risk for patients who are candidates for early operation. From an endoscopic perspective, these findings advocate for limiting stent duration when possible and carefully weighing the benefits and risks of PBD in each clinical scenario.
Study limitations
This study has several important limitations. It is a single-center study with a relatively small sample size (22 vs. 24), which limits the precision of clinical comparisons and the generalizability of the findings to other institutions. Operative and postoperative data were collected retrospectively, and residual confounding due to patient selection for PBD cannot be excluded (e.g., patients with higher bilirubin or perceived worse performance status may have been preferentially drained). The study also does not address the use of metal stents, longer stent dwell times (as seen in modern neoadjuvant protocols), or histologic recovery after stent removal. Furthermore, we did not formally assess inter-observer reproducibility of pathological assessments or morphometric measurements; however, all histology was reviewed by a single experienced pathologist to minimize variability.
The perioperative mortality rate in this cohort was 10.8% overall (9.1% in the PBD group vs. 12.5% in controls), which is higher than the institutional historical average of approximately 5% [25]. Although this difference was not statistically significant between groups, it likely reflects stochastic variation inherent in small sample sizes rather than a treatment effect. Selection bias favoring sicker patients for PBD cannot be ruled out as a contributing factor.
Conclusions
Despite these limitations, the prospective and standardized histologic assessment, along with quantitative digital morphometry, provide strong evidence that even short-term PBD using plastic stents leads to rapid, intense, and lasting PCF in humans. This research builds on and quantifies earlier animal studies and qualitative human observations, addressing a gap in the existing literature.
In conclusion, short-term PBD with plastic stents results in rapid, intense, and enduring PCF that levels off within the first week. Although this fibrotic response did not negatively impact surgical outcomes in this high-volume cohort, our findings establish a quantitative baseline for stent-induced injury and emphasize the need to avoid unnecessary preoperative drainage when prompt surgery is an option. Future multicenter studies with larger patient groups, extended histologic follow-up, and assessments of metal stents and neoadjuvant protocols will be essential to further elucidate the full range of stent-induced biliary changes and their clinical implications.
| Variable | Study group (n = 22) | Control group (n = 24) | p-value |
|---|---|---|---|
| CBD Area (µm2) | 40,155 ± 31,210 | 212,255 ± 104,435 | < 0.001 |
| Wall width (µm) | 6,554 ± 3,968 | 499 ± 111 | < 0.001 |
| Length (µm) | 8,888 ± 5,192 | 754 ± 214 | < 0.001 |
| Max diameter (µm) | 11,358 ± 6,821 | 754 ± 217 | < 0.001 |
| Max radius (µm) | 6,076 ± 3,660 | 408 ± 111 | < 0.001 |
| Perimeter (µm) | 61,843 ± 36,280 | 3,750 ± 1,124 | < 0.001 |
| Collagen area (µm2) | 25,315,550 ± 21,865,237 | 112,667 ± 77,843 | < 0.001 |
| Variable | Study group (n = 22) | Control group (n = 24) | p-value |
|---|---|---|---|
| Gray level (minimum) | 94.4 ± 28.0 | 67.5 ± 40.9 | 0.01 |
| Gray level (maximum) | 45.1 ± 26.1 | 0.9 ± 0.7 | < 0.001 |
| Gray level (red channel) | 93.2 ± 26.2 | 70.6 ± 44.9 | 0.04 |
| Gray level (green channel) | 105.2 ± 29.1 | 78.7 ± 47.1 | 0.03 |
| Variable | Study group (n = 22) | Control group (n = 24) | p-value |
|---|---|---|---|
| Specific complications | |||
| Surgical site infection | 4 (18.2) | 6 (25.0) | 0.57 |
| Intra-abdominal abscess | 2 (9.1) | 0 (0) | 0.13 |
| Pancreatic leak (grade B or C) | 2 (9.1) | 1 (4.2) | 0.49 |
| Bile leak | 0 (0) | 0 (0) | - |
| Phlebitis | 1 (4.6) | 1 (4.2) | 0.94 |
| Pneumonia | 5 (22.7) | 3 (12.5) | 0.36 |
| Pulmonary embolism | 1 (4.6) | 1 (4.2) | 0.94 |
| Deep vein thrombosis | 0 (0) | 0 (0) | - |
| Mortality (≤ 90 days) | 2 (9.1) | 3 (12.5) | 0.71 |
| Clavien-Dindo grade | 0.42 | ||
| Grade 0 (no complication) | 9 (50.0) | 5 (27.8) | |
| Grade 1 | 1 (5.6) | 2 (11.1) | |
| Grade 2 | 5 (27.8) | 9 (50.0) | |
| Grade 3 | 0 (0) | 0 (0) | |
| Grade 4 | 0 (0) | 0 (0) | |
| Grade 5 (mortality) | 2 (9.1) | 3 (12.5) |