Assessment of main pancreatic duct cutoff with dilatation, but without visible pancreatic focal lesion on MDCT: a novel diagnostic approach for malignant stricture using a CT-based nomogram
European Radiology 2022 Dec;32(12):8285-8295. doi: 10.1007/s00330-022-08928-8. Epub 2022 Jun 21.
Pancreatic ductal adenocarcinoma (PDAC) typically manifests as a hypoattenuating mass with upstream main pancreatic duct (MPD) dilatation on contrast-enhanced dynamic CT . However, it is not rare in clinical practice to encounter an isoattenuating PDAC, thereby manifesting only as an isolated MPD dilatation [2, 3]. In this situation, indirect secondary signs other than the interrupted duct sign for suspected hidden pancreatic malignancies gained importance [2, 4, 5].
This is a retrospective study focused on emphasizing useful tools to predict the presence of a hidden pancreatic karyogenetic mass in patients who don’t have a visible focal pancreatic lesion on CT, but present main pancreatic duct abrupt cutoff and dilatation.
The sample size comprised 92 patients from a CT database of a single large academic institution. The inclusion criteria were: abrupt cutoff of MPD associated with upstream dilatation, unidentified focal pancreatic lesion, histopathological confirmation or more than 2 years of stability on imaging surveillance. The exclusion criteria were: suboptimal image quality of CT and history of pancreatic surgery.
The following imaging findings were assessed: MPD cutoff site, parenchymal contour abnormality, maximum diameter of the MPD proximal to the duct cutoff site, presence of distal parenchymal atrophy, associated acute pancreatitis on CT and presence of pancreatic cystic lesions.
The clinical findings including new-onset diabetes mellitus (DM) and unintentional weight loss and laboratory findings including the serum level of carbohydrate antigen 19-9, amylase and lipase were also evaluated. After the histopathologic results or clinical follow-up, the sample was divided in two main groups: malignant (41,3%) and benign (58,7%).
Multivariable logistic regression analysis showed that CA19-9 elevation (odds ratio [OR] 7.5, 95% CI 2.0–28.6; p = 0.003), cutoff site at the head/neck (OR 7.6, 95% CI 1.8–32.3; p = 0.006), parenchymal contour abnormality at the duct cutoff site (OR 13.7, 95% CI 3.3–58.0; p < 0.001), and the presence of pancreatitis (OR 11.5, 95% CI 2.1–62.6; p = 0.005) were significant features for predicting the malignant group.
A combination of any two significant features showed an accuracy of 77.2%, and a combination of any three features exhibited a specificity of 100%. For predicting the probability of the malignant group, a CT-based nomogram was constructed based from the four significant features. This nomogram showed an area under the curve (AUC) of 0.84 (95% confidence interval [CI], 0.77–0.90). Therefore, a patient with three CT imaging features and CA19-9 elevation requires further diagnostic tests with aggressive management.
The authors acknowledge some limitations: its retrospective single-center design with a probable selection bias; the results are limited to the population of patients with MPD cutoff sign; histologic confirmation had only been achieved for seven patients in the benign group; the large portion of CT examinations in this study were not optimized for delineation of pancreatic abnormalities because most CT indications were unrelated to screening for PDAC, which might have lowered the sensitivity of each CT imaging feature; not performing an external analysis using an independent validation set to determine the thresholds for the ratios used to construct the nomogram; therefore, there is a need for further studies involving larger numbers of cases.
In conclusion, the authors have shown that a combination of three CT features (parenchymal contour abnormality, head/neck location of the duct cutoff site, and the presence of pancreatitis) and CA19-9 elevation facilitates the estimation of the probability of hidden pancreatic malignancy in patients with MPD abrupt cutoff and dilatations, but without visible pancreatic focal lesions on CT. This nomogram could contribute to a better selection of candidates for immediate further imaging studies using abdomen MRI with MRCP and/or EUS. Also, they have developed a CT-based nomogram that assesses the probability of the presence of pancreatic malignancy with excellent diagnostic performance (AUC of 0.84).
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Alexandra Hapca is a fifth-year Radiology Resident at County Emergency Clinical Hospital of Cluj-Napoca, Romania. She completed her undergraduate Μedical Doctor degree at "Iuliu Hatieganu" University of Medicine and Pharmacy in Cluj-Napoca. The abdominal and pelvic radiology is one of her main fields of interests in diagnostic imaging.
Comments may be sent to dr.alexandrahapca(at)gmail.com