PATIENTS AND METHODS

In the present prospective study, 60 patients with bile duct strictures of unknown aetiology were enrolled from April 1994 to December 1998. The trial included all patients endoscopically examined in this period who were referred to our hospital with bile duct strictures of unknown aetiology. The study protocol was approved by the local ethics committee of the University of Muenster and patients gave written informed consent to participate in the trial. We examined 32 men and 28 women, mean age 59.6 years (range 18–77). All 60 patients were prospectively examined by ERCP supplemented by IDUS and ETP. Because IDUS was always carried out before the assessment of ETP, physician performing IDUS did not have the histological diagnosis available until the procedures had been completed; therefore, the requirements of a blind study were satisfied.

A standard duodenoscope (Olympus JF-1T20; Olympus Optical Co, Ltd, Tokyo, Japan) was used for the transpapillary examination. Endoscopic papillotomy was performed if necessary. The 2.0 mm, 20 MHZ ultrasound probe (Aloka Co, Ltd, Tokyo, Japan) was inserted into the bile duct transpapillarily. A frequency of 20 MHZ provides an axial resolution of 0.1 mm and allows for maximum penetration of approximately 20 mm. The ultrasound miniprobe system used in the present study contains a 360° radial sector scanning transducer and an ultrasound generator with a motor unit and a display (SSD-550; Aloka Co) as reported previously.⁶ A wire guided probe was not used. After transpapillary insertion, the probe tip was fluoroscopically placed. IDUS criteria included evaluation of tumour margins, invasion of surrounding tissue, and invasion of vessels. Sonographic features such as inhomogeneous echo poor lesions with irregular tumour margins were considered indicative of malignancy whereas homogeneous echo rich masses with smooth margins were considered characteristic of inflammatory lesions. Endosonographic criteria used in the present study are the generally accepted criteria for describing bile duct tumours and tumours of the pancreas.^6,7 Penetration was defined as a continuation of the main echo poor tumour mass into adjacent structures. Tumours invading vascular structures or both hepatic ducts were classified as irresectable. No adverse events related to IDUS occurred during examination or follow up.

Transpapillary biopsies (n=4–8) were taken out of the biliary strictures by endoscopic forceps (MTW Endoscopy, Wesel, Germany). The tissue specimen was taken out of the bile duct stricture by either straight or angled endoscopic forceps. If insertion of the endoscopic forceps into the stricture was not possible, biopsies were taken from the lower margins of the bile duct stenosis. Histological analysis of the tissue specimens taken during endoscopy and surgery was performed at the Department of Pathology, and the specimens were independently assessed by two experienced pathologists. There were no complications resulting from taking tissue specimens transpapillarily. After performing IDUS and after assessment of the transpapillary biopsy, other imaging modalities (for example, computed tomography, endoscopic ultrasound, magnetic resonance imaging) were performed as required. All patients underwent laparotomy to exclude malignancy, and the final diagnosis was made by histological assessment of the surgical resection specimens (considered the gold standard).

RESULTS

Final diagnoses

In the present study series of 60 patients, the final diagnoses obtained from histopathological examination of the surgical specimen revealed 30 pancreatic carcinomas, 17 bile duct cancers, three gall bladder cancers, and 10 benign bile duct strictures (table 1⇓). Figure 1⇓ shows the allocation of the strictures modified according to the criteria of Tompkins and colleagues.⁹

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Table 1

Final diagnosis based on histological assessment of surgical resection specimens

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Figure 1

Topographic allocation of the bile duct strictures under study (total n=60). Modified according to the criteria of Tompkins and colleagues.⁹

Intraductal ultrasonography

IDUS allowed correct diagnosis of bile duct carcinomas with sensitivity and specificity rates of 88% and 86%, respectively (table 2⇑). For neoplastic lesions of pancreatic origin infiltrating the bile duct, IDUS had a sensitivity of 90% and a specificity of 83% (see fig 2⇓). For carcinomas originating in the gall bladder with infiltration of the bile duct, no separate statistical analysis was performed because of the small number of cases (n=3). ERCP supplemented by IDUS allowed for correct preoperative diagnosis in 83% of cases (50 of 60 patients, 48 patients with malignancies, two patients with non-malignant lesions), which is significantly superior to the accuracy of ETP (60%; p=0.008). By combining ETP with IDUS (table 2⇑), a correct preoperative diagnosis was made in 59 of 60 patients (49 patients with malignancies, 10 patients with non-malignant lesions) resulting in an accuracy rate of 98%. Forty eight of 50 cases (92%) with a final diagnosis of “malignancy” (obtained from histopathological examination of the surgical specimen) had endosonographically been classified as clearly malignant according to the IDUS criteria mentioned above. IDUS did not show typical endosonographic features of malignancies in two of these 50 patients. In these two patients the differential diagnosis was pancreatic carcinoma versus inflammatory lesion in the head of the pancreas by IDUS criteria (fig 3⇓).

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Figure 2

A 67 year old male with pancreatic cancer. The patient initially presenting with obstructive jaundice was referred to our hospital for further diagnostics. (A) Endoscopic retrograde cholangiopancreatography suggested a malignant biliary obstruction. (B) Intraductal ultrasonography showed a suspected malignant mass (arrows) infiltrating the common bile duct. L, lumen of the common bile duct; HA, hepatic artery. (C) Histological analysis of a tissue specimen taken by transpapillary biopsy showed an adenocarcinoma with atypical clusters of stroma free epithelial cells (haematoxylin and eosin, ×200).

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Figure 3

Intraductal ultrasonography. Benign stricture of the proximal common bile duct in a 46 year old female patient showing typical ultrasonographic characteristics of an inflammatory lesion: homogeneous echo rich mass with smooth margins (arrows).

Comparing IDUS and ETP with regard to localisation of biliary stenoses (proximal, middle, and distal third), McNemar's test proved IDUS to be superior to ETP in the diagnostics of distal biliary stenoses (p=0.022). Because of the small number of cases, no statistically significant difference was found between IDUS and ETP in bile duct strictures of the proximal (n=12) and mid third (n=7) (table 3⇓).

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Table 3

Exact 95% confidence interval and McNemar's test of endoscopic transpapillary biopsy (ETP) and intraductal ultrasonography (IDUS) with respect to localisation of biliary stenoses

DISCUSSION

Diagnosis of strictures affecting the biliary tract using non-surgical methods is highly desirable to allow for adequate planning of surgical or non-surgical treatments.^10,11 Although many patients are managed without histological confirmation, confirmation allows accurate decision making with reference to total patient management, including surgery, endoscopic stenting, chemotherapy, or radiotherapy.¹⁰ Brush cytology is considered an accurate technique in providing a cytopathological diagnosis of bile duct strictures. However, recently published studies on brush cytology or transpapillary forceps biopsy of bile duct strictures did not compare these techniques with histopathology of resection specimens in all patients.^3,12,13 In the present study, all of the 60 patients underwent surgery thus allowing an accurate evaluation of the techniques.

In the past decade, several attempts have been made to examine bile duct strictures endoscopically.^12–,¹⁷ For brush cytology, a sensitivity of 56%, specificity of 91%, and an accuracy rate of 65% were reported (n=86, histopathologically proved n=35).³ However, results for ETP from four prospective studies have been encouraging,^10,12,17,18 with a cancer detection rate of 65% among 275 patients.¹¹ Regarding sensitivity and specificity, our results match with those of Pugliese and colleagues, with a sensitivity of 52% (present study) compared with 53%, a specificity of 100% in both series, and an accuracy of 60% versus 68%.¹⁰

However, a diagnosis of malignancy can only be determined by the pathologist when invasion of tumour cells into the stroma is seen in the biopsy specimen. As many biopsies from bile duct strictures contain only clusters of epithelial cells without underlying stroma, it is impossible for the pathologist to prove invasive growth of the tumour which is, by definition, the criterion for malignancy. High grade dysplasia of epithelial cells suggests malignancy but does not prove invasion.

Endoscopic ultrasonography (EUS) has made an impressive impact on endoscopic imaging. Moreover, recently developed ultrasonic miniprobes can be passed through the working channel of standard endoscopes to provide high frequency ultrasonographic images. The ultrasonic miniprobe is an ideal instrument to be inserted into fluid filled tubular structures such as the biliary and pancreatic ductal systems that are only slightly larger than the miniprobe itself.⁵

In a previous study by Menzel et al, conventional endosonography (EUS) was compared with IDUS in biliary strictures.¹⁹ The present study evaluated the impact of ETP and IDUS on the diagnosis of biliary strictures. EUS was not regularly performed in all patients included in this trial. The aim and techniques used in the present study differed substantially from those of Menzel et al as ETP were taken, and both ETP and IDUS were performed in the same session during ERCP. Therefore, more information—histology and staging of the tumour—about the bile duct strictures are obtained during a single endoscopic examination (ERCP).

In a previous study by Tamada et al, IDUS used for bile duct cancer diagnosis gave an accuracy of 76%.²⁰ In this study however IDUS was not compared with the histomorphology of surgical resection specimens. This fundamental limitation of many studies concerning imaging of the bile duct is due to the difficulty in comparing imaging results with histological analysis of resected specimens as most patients with benign bile duct stenoses do not undergo surgery.²⁰

Compared with standard EUS, intraductal scanning within the bile duct stricture improved diagnostic accuracy as well as estimation of local tumour extent.¹⁹ Although ultrasonography does not provide histopathological diagnosis, IDUS yields specific tissue characterisation and thus may direct the diagnostic process to the underlying disease.^6,7,20 In the present study, the combination of IDUS and ETP allowed correct preoperative diagnosis in 98% of cases, making ERCP—supplemented by these two techniques—the most accurate and reliable procedure in preoperative evaluation of biliary strictures.

Tumour staging relies on precise delineation of the local extent and on detection of lymph nodes and distal metastases to provide a guideline for prognosis and treatment. As shown previously, endoluminal ultrasonography is generally accurate for staging the tumour category. Due to the limited ultrasonic penetration for both IDUS and EUS, understaging of biliary carcinomas in the proximal bile duct and bile duct bifurcation has been observed.¹⁹ Application of high ultrasound frequencies enhances the resolution but reduces the depth of penetration. Thus IDUS is not suitable for lymph node staging. The staging information from the present trial (preoperative histology, assessment of local tumour extension) has been used for clinical care decision in patients with bile duct strictures. Due to the lack of information regarding lymph node stage and distal metastases however, IDUS and ETP by themselves do not allow for a complete evaluation on resectability. Nevertheless, they do contribute to more accurate decision making with reference to total patient management.

In conclusion, ERCP provides a unique opportunity to obtain histological specimens from patients with biliary strictures of unknown aetiology and, additionally, allows for biliary decompression. Preoperative assessment of tissue samples from strictures affecting the biliary tract may permit more accurate decision making in total patient management. Accuracy of ETP alone is not reliable enough to allow for a definitive preoperative diagnosis of bile duct strictures. ETP complemented by IDUS can achieve a significant improvement in preoperative diagnosis. Thus in patients with bile duct strictures, ERCP plus IDUS, ETP, and the option to drain the bile duct system can provide biliary decompression as well as a diagnosis of malignancy with a high degree of accuracy.