GASTROINTESTINAL

CTand MR imaging of multilocular acinar cell cystadenoma:comparison with branch duct intraductal papillary mucinousneoplasia (IPMNs)

Christophe Delavaud & Gaspard d’Assignies & Jérome Cros & Philippe Ruszniewski &Pascal Hammel & Philippe Levy & Anne Couvelard & Alain Sauvanet & Safi Dokmak &

Valérie Vilgrain & Marie-Pierre Vullierme

Received: 1 December 2013 /Revised: 19 March 2014 /Accepted: 15 May 2014# European Society of Radiology 2014

AbstractObjectives To describe CTandMR imaging findings of acinarcell cystadenoma (ACC) of the pancreas and to compare themwith those of branch duct intraductal papillary mucinousneoplasia (BD-IPMN) to identify distinctive elements.Methods Five patients with ACC and the 20 consecutivepatients with histologically proven BD-IPMNwere retrospec-tively included. Clinical and biological information was col-lected and histological data reviewed. CT and MR findingswere analysed blinded to pathological diagnosis in order toidentify imaging diagnostic criteria of ACC.Results Patients with ACC were symptomatic in all but onecase and were younger than those with BD-IPMN (p=0.006).Four radiological criteria allowed for differentiating ACCfrom IPMN: five or more cysts, clustered peripheral smallcysts, presence of cyst calcifications and absence of commu-nication with the main pancreatic duct (p<0.05). Presence of

at least two or three of these imaging criteria had a strongdiagnostic value for ACC with a sensitivity of 100 % and80 % and a specificity of 85 % and 100 %, respectively.Conclusions Preoperative differential diagnosis betweenACC and BD-IPMN can be achieved using a combinationof four CT and/or MR imaging criteria. Recognition of ACCpatients could change patient management and lead to moreconservative treatment.Key Points• Four imaging findings are associated with acinar cellcystadenoma (ACC).

• Imaging could achieve differential diagnosis between ACCand BD-IPMN.

• Diagnosis on imaging would change patient managementand avoid surgical resection.

Keywords Pancreatic cysts . Magnetic resonanceimaging . Computed tomography . Imaging . Diagnosis

AbbreviationsACC Acinar cell cystadenomaBD-IPMN Branch duct intraductal papillary

mucinous neoplasiaMDCT Multidetector computed tomographyMRCP Magnetic resonance cholangiopancreatographyOR Odds ratioPAS Periodic acid stainSD Standard deviation

Introduction

Acinar cell cystadenoma (ACC), also known as acinar cystictransformation of the pancreas, is an uncommon pathological

C. Delavaud (*) :G. d’Assignies :V. Vilgrain :M.<P. VulliermeService de Radiologie, Hôpital Beaujon, 100, Boulevard du GénéralLeclerc, 92118 Clichy Cedex, Francee-mail: christophe.delavaud@hotmail.fr

J. CrosService d’Anatomopathologie, Hôpital Beaujon, 100, Boulevard duGénéral Leclerc, 92118 Clichy Cedex, France

P. Ruszniewski : P. Hammel : P. LevyService de Pancréato-Gastro-Entérologie, Hôpital Beaujon, 100,Boulevard du Général Leclerc, 92118 Clichy Cedex, France

A. CouvelardService d’Anatomopathologie, Hôpital Bichat, 46, Rue HenriHuchard, 75877 Paris Cedex 18, France

A. Sauvanet : S. DokmakService de Chirurgie Hépato-Pancréato-Biliaire, Hôpital Beaujon,100, Boulevard du Général Leclerc, 92118 Clichy Cedex, France

Eur RadiolDOI 10.1007/s00330-014-3248-0

entity that was first described in 2002 [1–3]. ACC is a benigncystic epithelial lesion lined with cells that are morphologi-cally and immunohistochemically similar to acinar cells. Theorigin of ACC is still a subject of debate. Although it wasinitially considered to be a non-neoplastic entity, such as adevelopmental anomaly or postobstructive glandular dilata-tion [3], more recent pathological studies suggest that it is aneoplastic lesion and could be the benign counterpart of acinarcystadenocarcinoma of the pancreas [1, 3–5].

ACC may present as a unilocular lesion but is more fre-quently a multilocular lesion. Thirty-six cases (including 21with a multilocular presentation) have been reported in theliterature [1–10]. None of these cases were correctly diag-nosed preoperatively and multilocular ACCs were usuallymisdiagnosed as branch duct intraductal papillary mucinousneoplasia (BD-IPMN). The pathological diagnosis of ACC isbased on macroscopic, histological, histochemical and immu-nohistochemical findings, and this entity can easily be distin-guished from other cystic lesions including BD-IPMN. On theother hand, little is known about the imaging features of ACCbecause they have only been reported in one case report (withCTand MR imaging) [6], four cases (with only CT) [7, 9] andone series of ten patients (with a few imaging descriptions,including seven patients with multilocular lesions) [5].

Because it is a benign condition that is not aggressive,correct diagnosis of ACC on imaging would certainly changepatient management and prevent pancreatic resection in mostof these patients.

Thus, the goals of this study were to (1) retrospectivelydescribe the features of multilocular ACC on CT and MRimaging, (2) compare CT and MR findings in ACC withBD-IPMN to identify distinct findings.

Materials and methods

This retrospective single-centre study was performed in atertiary hospital for pancreatic diseases and was approvedwitha waiver of informed consent by the local institutional reviewboard. The study included patients with ACC who werecompared to patients BD-IPMN in a 1:4 ratio.

Study design

ACC patients

This retrospective study included all patients with a patholog-ical diagnosis of multilocular ACC who underwent a preop-erative contrast-enhanced CTandMR examination from 1996to 2012, found in the database of the pathology department ofour institution. Pathological diagnosis of ACC was based onpreviously described criteria: multilocular cystic lesion withan epithelial lining of typical acinar cells, the presence of

eosinophilic periodic acid stain (PAS)-positive cytoplasmicgranules, and immunohistochemical acinar markers(cytokeratin 7 and trypsin) without cellular atypia [3]. Fivepatients with ACC (four women and one man; mean age,38.8 years old; range, 26–59) were included. Surgical proce-dures included a Whipple procedure and a left and totalpancreatectomy in two, two and one patients, respectively.Four patients had chronic abdominal pain, which led to imag-ing examinations and the lesion was discovered incidentally inone patient. The preoperative diagnosis was BD-IPMN in allcases.

BD-IPMN patients

Patients with pathologically confirmed, benign BD-IPMNwith no main duct involvement and had undergone preopera-tive contrast-enhanced CT and MR examinations between2005 and 2008 were included.

Twenty patients (11 women and 9 men; mean age,57.9 years old; range, 25–79) fulfilled the inclusion criteria.Fifteen patients underwent pancreatic enucleation and fivepatients underwent a Whipple procedure. The reasons forsurgery were acute pancreatitis, a suspected intracystic nod-ule, an increase in cyst size, and a cyst size of more than 3 cmin 11, 2, 2 and 5 patients, respectively.

Clinical and biological data collection

Data were extracted from the medical records of ACC andBD-IPMN patients. Clinical data included age, gender, symp-toms (including pancreatic pain, defined as an upper abdom-inal pain radiating to the back and jaundice), episodes of acutepancreatitis (pancreatic pain and serum lipase more than threetimes the upper limit of normal), presence of diabetes mellitusand the presence of exocrine pancreatic insufficiency. Routinebiological tests included blood cell count, liver enzymes,serum bilirubin, serum lipase and C-reactive protein. Allpatients underwent clinical and imaging follow-upexaminations.

Histopathological diagnosis

The five cases of ACC were analysed retrospectively by apathologist experienced in pancreatic diseases (JC, 8 years ofexperience), who confirmed the diagnosis of multilocularACC in all patients based on previously described criteria[1, 3–5]. Briefly, on gross pathology, ACC appears as well-circumscribed cysts containing serous fluid, without solidareas, papillary projections or abnormalities of the adjacentpancreas. Microscopic examination shows multiple cystslined by typical acinar cells with apical deeply eosinophilicperiodic acid–Schiff-positive granules with no cellular atypia.The Ki67 index was low and there was no nuclear positivity

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for the p53 tumour-suppressor gene. The presence of thecriteria mentioned above was assessed in the formalin-fixedparaffin-embedded specimens.

The pathologist also reviewed the resected BD-IPMN spec-imens and confirmed the diagnosis based on consensuscriteria [11, 12]. The diagnosis was confirmed in the presenceof papillary proliferation of epithelial cells in the branch ductswithout main duct involvement. Different types of cell differ-entiation were possible (gastric, intestinal, pancreatobiliary oroncocytic). No malignant transformation was recorded.

CT and MR imaging

CT and MR examinations were available for all patients withACC and BD-IPMN. The median delay between imaging andsurgery was 5 months (range, 2–9) in the ACC group and3 months (range, 0–12) in the BD-IPMN group.

CT examinations were performed with the following sys-tems: BrightSpeed, HighSpeed Advantage, LightSpeed QX/I,LightSpeedVCT (GEHealthcare, Milwaukee,WI, USA), andSensation 16 system (Siemens, Erlangen, Germany). Afterunenhanced CT was performed, each patient received 2 mLper body weight of non-ionic contrast material through an 18-gauge angiographic catheter inserted into a forearm vein.Contrast material was injected at 3 mL/s using an automaticpower injector. Helical CT was performed using a single-detector system with the following parameters: 5-mm colli-mation, 1:1 table pitch, and 5-mm reconstruction intervals inone patient. Multidetector CT (MDCT) was used in the other24 patients with the following parameters: 0.6-mm detectorcollimation and 2.5-mm slice reconstruction. Multiphasic he-lical CT images were obtained at 40 s (pancreatic phase), andat 70 s (portal venous phase) after beginning contrast injec-tion. MR examinations were performed with 1.5-Tsuperconducting MR systems using a four-channel phasedarray coil: Gyroscan ACS-NT and Ingenia (Philips MedicalSystem, Best, the Netherlands), and Sigma (GE HealthCare,Milwaukee, WI, USA). The MR protocol included transverseand coronal T2-weighted imaging with a single-shot fast spin-echo sequence, a transverse breath-hold 3D T1-weighted fat-suppressed spoiled gradient-recalled-echo (dynamicgadolinium-enhanced) sequence before and after dynamicinjection of 0.1 mmol/kg of body weight of gadolinium che-lates with a power injector at a rate of 2–2.5 mL/s. Contrast-enhanced images were acquired in the pancreatic (35–45 safter injection), portal venous (75–80 s after injection) andd e l a y e d ( 1 80 s a f t e r i n j e c t i o n ) p h a s e s . MRcholangiopancreatography (MRCP) was performed in all pa-tients with a breath-hold 2D half-Fourier RARE heavily T2-weighted pulse sequence on the coronal or coronal obliqueplane that best depicted the pancreatic duct system and thebiliary tree. In addition, coronal respiratory-triggered 3D half-

Fourier RAREMRCPwas also performed in 2/5 (40 %) ACCpatients and in 7/20 (35 %) BD-IPMN patients.

Image analysis

Two radiologists (CD and GA, with 4 and 8 years of experi-ence in gastrointestinal radiology, respectively) independentlyreviewed the CT and MR images at a picture archiving andcommunication system workstation. They were unaware ofthe histopathological diagnosis (ACC or BD-IPMN).

Image analysis included assessment of features derivedfrom the radiological case reports and pathological data forACC, which were considered to be recognizable on imaging[3, 5–7] and imaging findings previously described in IPMN[13–15]. The following imaging findingswere analysed: num-ber of cysts recorded as less than or at least five, size of thelargest cyst, predominant shape of the cyst (round or elongat-ed), presence of “clustered small cysts” (as described onpathology [3, 5]; central (next to the main pancreatic ducts)or peripheral (on the periphery of the pancreatic parenchy-ma)), location in the pancreatic gland (head, uncinate process,body and tail), presence of cyst calcifications on unenhancedCT images [3, 5, 9], presence of endoluminal filling defects oneither T2-weighted or post-contrast T1-weighted MR se-quences, communication of the lesions with the main pancre-atic duct (defined as a channel that connected the pancreaticcyst to the main pancreatic duct), and dilatation of the mainpancreatic duct (greater than 3 mm in diameter [16]). Inflam-matory pancreatic changes and signs of malignancy such asthickening of the cyst wall, presence of mural nodules or soft-tissue mass in the cyst, presence of vascular encasement, peri-pancreatic lymph node enlargement and extra-pancreatic in-vasion were also searched for. A consensus was reached ondiscordant imaging findings.

Statistical analysis

Clinical and imaging characteristics were recorded for the twogroups. Data were double-keyboarded and analysed usingSTATA software version 11 (Stata Corporation, CollegeStation, TX, USA). Quantitative variables were reportedas mean ± standard deviation (SD) and qualitative variablesas numbers (%).

The clinical and imaging characteristics of patients withACC and BD-IPMN were compared on univariate analysisusing the chi-square test or Fisher’s exact test, as appropriate.All tests were two-tailed and p values less than 0.05 wereconsidered to be statistically significant. Odds ratios (ORs)were estimated with their 95 % confidence intervals (95 %CIs), using logistic regression models. Multivariate analysiscould not be performed because of the small number of ACCpatients (n=5). However, all variables with p values less than0.05 on univariate analysis were used to build a simple-to-use

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score to predict the diagnosis of ACC. One point was assignedto each variable. Sensitivity and specificity of the differentcut-off levels of the score were calculated.

Results

Clinical, biological findings

The clinical findings for the patients with ACC and BD-IPMNare described in Table 1. Briefly, patients with ACC wereyounger than those with BD-IPMN (38.8 vs. 57.9 years old,p=0.0059). Patients in both groups were frequently symptom-atic (80 % and 55 %, in the ACC and BD-IPMN groupsrespectively p=0.30). Blood cell count, liver enzymes, serumbilirubin, serum lipase and C-reactive protein were normal inall patients except during episodes of acute pancreatitis.

Imaging findings

Imaging findings for the ACC and BD-IPMN patients aresummarized in Table 2.

Typical cysts were found in ACC patients on CT and MRI(liquid attenuation and signal) with thin walls and no visibledeposits or endoluminal defects (Figs. 1 and 2). No inflam-matory pancreatic changes, cyst wall thickening, mural nod-ules or soft-tissue masses were found in the cyst. Vascularencasement, peri-pancreatic lymph node enlargement andextra-pancreatic invasion were not observed.

Four imaging findings were observed statistically moreoften in ACC than in BD-IPMN patients on univariate anal-ysis (Table 2, Fig. 3): five or more cysts, clustered peripheralsmall cysts, presence of cyst calcifications and absence of

communication with the main pancreatic duct. A score basedon the presence of any of these imaging findings was thencomputed by linear combination. Table 3 shows the sensitivityand the specificity of the different cut-off levels and Fig. 4summarizes the main imaging findings for ACC and BD-IPMN.

Follow-up

All patients in the ACC group underwent serial clinical andimaging follow-up examinations for 2 to 11 years (mean,5.5 years). No recurrence was observed; however, two pa-tients remained symptomatic with pancreatic pain.

In the BD-IPMN group, all patients underwent serial clin-ical and imaging follow-up examinations for 2 to 8 years(mean, 4.9). Nineteen patients (95 %) were symptom-free.One patient had recurrent acute pancreatitis during follow-up. No recurrence was noted on imaging.

Discussion

Because ACC has been misdiagnosed as BD-IPMN in mostprevious reports [3, 5, 6, 9], this study compared the clinicaland imaging features of ACC and BD-IPMN for the first time.This study has identified features that can help characterizeACC and optimize patient management.

As expected from previous studies in ACC [1–10], most ofour ACC patients were young women. There was no statisti-cally significant gender predominance in our two populations.Nevertheless, large cohort studies of patients with IPMNinitially showed that IPMN mostly affected men. However,this is no longer found and the sex ratio in IPMNs is estimatedto be 1:1 at present [13, 17, 18]. Interestingly, age at diagnosiswas significantly different in the ACC and BD-IPMN groups(mean age, 39 vs. 58 years), which is consistent with bothdiseases [1–9, 13]. Although it was not significant, most ofour ACC patients had pain. This has already been reported inthe literature [1, 3, 5, 8–10], but its physiopathology is stillunknown. In our series, the presence of pain was not related tocyst size.

We identified four imaging findings to discriminate be-tween ACC and BD-IPMN: five or more cysts, clusteredperipheral small cysts, presence of cyst calcifications andabsence of communication with the main pancreatic duct.All of our ACC patients had more than five cysts but the meansize of the largest cyst was not different in ACC and BD-IPMN patients. This is more a reflection of extensive involve-ment of the pancreas in ACC patients than in BD-IPMN. Inour series, 60 % of ACC patients had cysts both in the headand body or tail of the pancreas compared to 20 % of our BD-IPMN patients.

Table 1 Patient characteristics in ACC and IPMN groups

Patients ACC(n=5)

BD-IPMN(n=20)

p valuea

Clinical features

Gender: male/female 1/4 8/12 0.4

Age (years) 38.8 [26–47] 57.9 [35–79] 0.0059

Diabetes mellitus 1 (20 %) 0 0.04

Exocrine pancreaticinsufficiency

0 0 –

Symptoms

Pancreatic pain 4 (80 %) 11 (55 %) 0.30

Acute pancreatitis 2 (40 %) 11 (55 %) 0.54

Jaundice 0 0 –

Data are numbers (%) or means [range]a p value obtained using chi-square test or Fisher exact or non-parametricKruskal–Wallis test as appropriate

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Fig. 1 Fortuitously discovereddiffuse cystic lesions of thepancreas in a 37-year-old manwho underwent caudalpancreatectomy. a, bCoronal MRcholangiopancreatography andsingle-shot T2-weighted MRimages showing multiple cysts ofvarious size involving the wholepancreas. The cysts are distantfrom the main pancreatic ductwhich remains of normal size(arrow). The largest cysts arelocated in the head of thepancreas. c Unenhanced axial CTimage showing cysticcalcifications in the uncinateprocess of the pancreas. Axialsingle-shot T2-weighted MRimage (d) correlated to grosspathology (e) after caudalpancreatectomy: presence ofclustered peripheral small cysts inthe pancreatic tail (arrowhead).Pathology confirmed thediagnosis of ACC

Table 2 Imaging findings inACC patients and IPMN patients

Numbers in parentheses arepercentagesa Total number with a location inthe pancreas is greater than 100 %because multiple sites areinvolved in some patientsb Odds ratios with their 95 % con-fidence intervals were estimatedusing logistic regressioncP value by the chi-square test orthe Fisher’s exact test, asappropriate

Patients withACC (n=5)

Patients withBD-IPMN (n=20)

Odds ratio[95 % CI]b

P valuec

≥5 cysts 5 (100) 4 (20) 20.4 [2.3–∞] 0.004

Mean size of the largestcyst in mm (SD)

19.8 (13.5) 18.3 (9.5) 1.01 [0.9–1.12] 0.95

Predominant shape

Elongated 2 (40) 12 (60) 0.4 [0.06–3.3] 0.42

Round 3 (60) 8 (40) 2.2 [0.2–31.7] 0.62

Clustered small cysts

Peripheral 4 (80) 0 48.4 [4.7–∞] <10−4

Central 0 0 – –

Location in the pancreatic glanda

Head (including uncinate process) 5 (100) 13 (65) 3.2 [0.4–∞] 0.27

Isthmus 1 (20) 3 (15) 1.4 [0.02–24] 1

Body 3 (60) 6 (30) 3.3 [0.3–49.5] 0.31

Tail 3 (60) 4 (20) 5.5 [0.5–87.4] 0.11

Cyst calcifications 4 (80) 0 (0) 48.4 [4.7–∞] <10−4

Absence of communication withmain pancreatic duct

4 (80) 3 (15) 18.7 [1.3–1,167] 0.01

Absence of main pancreatic ductenlargement

5 (100) 14 (70) 2.5 [0.3–∞] 0.29

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Fig. 2 Cystic lesion of theuncinate process in a 41-year-oldwoman revealed by acutepancreatitis treated by Whippleprocedure. a, b Contrast-enhanced MDCT at the portalvenous phase with curvilinearreformation showing multipleperipheral small cysts (arrow).The cysts remain distant from themain pancreatic duct (MPD) andno communication is seen withthe MPD (arrowhead). c, d Axialcontrast-enhanced MDCT at theportal venous phase and single-shot T2-weighted MR imageshowing multiple small cystsclustered in the uncinate process.e Microscopic examination ofpathology specimen showsmultiple cysts lined by typicalacinar cells with apical deeplyeosinophilic periodic acid–Schiff-positive granules without cellularatypia (arrows)

Fig. 3 Asymptomatic 79-year-old woman who had preoperativediagnosis of BD-IPMN. Whipplesurgery was performed becausecysts increased in size. CoronalMR cholangiopancreatography(a), axial (b) and coronal (c)single-shot T2-weighted MRimages showing elongated cystsin the pancreatic head.Communication with the MPD isnoticed (arrowhead). d Grosspathology specimen showing thebranched duct cysts within thepancreatic head (arrow).Diagnosis of BD-IPMN wasconfirmed by pathology

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All of our ACC patients had clustered peripheral cysts onimaging while this finding was not observed in BD-IPMNpatients. Although this finding seems to be specific for ACC,the small number of patients in our study makes it impossibleto draw firm conclusions and this must be confirmed in furtherstudies. Interestingly, this finding is strongly correlated topathological findings and could be seen but was not reportedin one case report [6]. Because ACC originates from acini andBD-IPMNs are dilated ducts between the pancreatic paren-chyma, this finding may be a sign of enlargement of the acinarpancreatic component, with little parenchymal separation ofthe cysts.

In our series, the presence of calcifications was found inmost ACC patients but no BD-IPMN patient. Calcificationswere reported in 3/10 (30 %) cases of ACC on CT scan [3, 9]and in certain pathological reports [3, 5]. On pathology, theyare often associated with protein calcifications that couldrepresent end-stage protein plugs. Although the mechanismis unclear, an imbalance in acinar secretion could lead toprotein precipitation and aggregation. Conversely, calcifica-tions are occasionally found in BD-IPMN. They have beenreported in 11–16 % of all BD-IPMNs and 6.5–9.5 % ofbenign BD-IPMNs [19–21]. The origin of the calcificationsis probably different for each disease. In IPMN, they corre-spond to calcifying obstructive pancreatitis caused byprolonged partial obstruction of the pancreatic duct [22].

Cyst communication is one of the hallmarks of BD-IPMNand was observed in 85 % of the patients with BD-IPMN.Conversely, cyst communication was only found in 1/5 (20%)

ACC patients. This is consistent with published reports wherecommunication between the cyst and the main pancreatic ductwas only reported in one patient onMR [5] and in two patientson endoscopic retrograde cholangiopancreatography [3]. In-terestingly in these cases, communication was very limited.Obviously, ductal communication cannot be excluded withcertainty when cysts are very close to the main pancreaticduct. In this case, other imaging findings or presence of cystsdistant to the main pancreatic duct may help diagnose ACC.Normal acinar structures communicate with the main ductthrough the centroacinar duct and the branched ducts thatprogressively increase in size. Because ACC is derived fromnormal acini, it physiologically communicates with the mainduct, but an absence of communicating duct dilatation is adifferentiating feature with BD-IPMN. Acinar secretion maynot be enough to dilate the ducts, or cyst formation could bedue to local protein aggregation that does not affect down-stream ducts.

On the basis of the four imaging findings (five or morecysts, clustered peripheral small cysts, presence of cyst calci-fications and absence of communication with the main pan-creatic duct) that were statistically different between ACC andBD-IPMN patients, we evaluated the sensitivity and specific-ity of combining those criteria in our two patient groups. Wefound that the presence of at least two or three of theseimaging criteria had a strong diagnostic value for ACC witha sensitivity of 100 % and 80 % and a specificity of 85 % and100 %, respectively. Indeed, further validation of these criteriaand their combination is needed. Since the exact nature ofACC (dystrophic or neoplastic) is not clearly defined yet,these lesions should be followed. Suspecting the diagnosison imaging, especially in cases with diffuse involvement ofthe pancreas, should lead to a surgical biopsy under laparos-copy with frozen section examination avoiding extensivepancreatic resection. The diagnosis may be very difficult toobtain using ultrasound-guided fine needle aspiration as ACClining cells are a true mimic of normal acinar cells.

Our study has certain limitations. First, there were very fewACC patients because of the rarity of the disease. Neverthe-less, the comparison of the imaging findings between ACCand BD-IPMN patients was blinded. Our control group was

Table 3 Sensitivity and specificity of the different cut-off criteria for thediagnosis of ACC

Sensitivity (%) Specificity (%)

At least 1 finding 100 60

At least 2 findings 100 85

At least 3 findings 80 100

4 findings 60 100

Imaging findings were the presence of any of these: five or more cysts,clustered peripheral small cysts, cyst calcifications and an absence ofcommunication with the main pancreatic duct

Fig. 4 Drawings representing the typical imaging features of ACC (a):more than five cysts, with clustered peripheral distribution, cysts calcifi-cations (black star) and no communication with the main pancreatic duct

and BD-IPMN (b): isolated or clustered cysts communicating with themain pancreatic duct without calcification

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limited to patients with BD-IPMN because ACC is usuallymistaken for BD-IPMN. We could have included other cysticlesions of the pancreas but we felt that this would not havereflected clinical practice. Imaging and pathological aspects ofacinar cell carcinoma with intraductal growth or papillarypatterns may mimic IPMN [23, 24]. These malignant entitiesare often unique and present with mural nodule, cyst wallcontrast enhancement—features that are absent in ACC. Clas-sical serous cystadenoma is theoretically a differential diag-nosis of ACC but is mostly a solitary lesion except in patientswith von Hippel–Lindau disease (VHL) and has rather spe-cific imaging features that do not overlap with ACC. Incontrast, macrocystic serous cystadenoma or mucinouscystadenoma may be mistaken for the unilocular form ofACC but not for the multilocular form described here. Wetherefore did not include these entities in this study. Pancreaticintraepithelial neoplasia (PanIN) has been reported in thesurgical specimens of five ACC cases out of ten [5]. Theselesions were distant from the ACC and can also be found nearIPMN. PanIN are small entities (smaller than 5 mm by defi-nition [12]). They may only be seen on endoscopic ultrasoundin some cases [25] but not on CT or MRI. They therefore donot represent a differential diagnosis and were not included inthis study.

Second, different imaging protocols were used in ACCpatients because of the large time frame. However, all of ourpatients underwent helical CT and MRI examinations includ-ing MRCP, which allowed us to analyse all imaging criteriaobserved in cystic pancreatic lesions (calcifications and cystcommunication).

In conclusion, this comparison of CT and MRI findings inACC and BD-IPMN patients showed that four imagingcriteria and their combination have a strong predictive valuefor the diagnosis of multilocular ACC. Conservative treatmentis indicated in patients who are diagnosed with ACC even ifpathological confirmation is still needed at the moment.Follow-up of these lesions is necessary until their nature isclearly defined.

Acknowledgements The scientific guarantor of this publication is Pro-fessor Valérie Vilgrain. The authors of this manuscript declare no rela-tionships with any companies whose products or services may be relatedto the subject matter of the article. The authors state that this work has notreceived any funding. One of the authors has significant statistical exper-tise. Institutional review board approval was obtained. Written informedconsent was waived by the institutional review board. Methodology:retrospective, case–control study, performed at one institution.

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