Keywords
pancreas - pancreatic ductal pattern - ansa pancreatica - pancreas divisum - magnetic
resonance cholangiopancreatography
Introduction
Pancreatitis has been described as a serious and often fatal disease. It can present
in acute or chronic form. There are several causes for chronic pancreatitis. Morphological
anomalies of the pancreatobiliary system have been described as one of the predisposing
factors for chronic pancreatitis.[1] Dawson and Langman[2] studied the anatomical patterns of the pancreatic ductal system in adults by dissection,
and classified them into four groups: embryonic type, patent accessory duct, ansa
pancreatica and obliterated accessory duct. The anatomical variations of the accessory
pancreatic duct (APD) were studied by dissection in terms of its shape, course, opening
into the duodenum, patency and communication with the main pancreatic duct (MPD).[3]
[4] Sunjida Shahriah et al[3] studied in detail the course of the APD (describing it as straight, spindle and
cudgel) and its communication with the MPD radiologically using Barium X-ray.
The importance of the anatomical variants of the pancreatic ductal system and anomalous
pancreatobiliary union was described radiologically using endoscopic retrograde cholangiopancreatography
(ERCP).[5] Magnetic resonance cholangiopancreatography (MRCP) was described as a better method
of visualizing the pancreatic and biliary ductal anatomy compared with the ERCP, since
it is non-invasive and safer.[6]
[7] However, the literature on the aforementioned anatomical patterns of the pancreatic
ductal system and its variants by cadaveric dissection substantiated along with radiological
studies using MRCP is not available for the Indian population. Our aim is to study
the prevalence of the pancreatic duct patterns in the Indian population by cadaveric
dissection and by MRCP.
Materials and Methods
Ethical clearance from the Institutional Review Board was obtained.
Cadaveric Study
A total of 15 adult pancreas and 5 fetal pancreas specimens of different gestational
ages (26 to 38 weeks) were obtained from cadavers donated to the Department of Anatomy
of our institution for the purpose of teaching and research; they were dissected by
the piecemeal method. The pancreatic ductal system was colored with acrylic paint
for better visualization.
In the adults, the presence or absence of the major and minor duodenal papillae was
studied. The number of pancreatic ducts, the length of the MPD, and its opening into
the duodenal wall in human adult pancreas specimens were studied. The presence or
absence of an APD, its pattern and communication with the MPD, and its opening into
the duodenal wall in human adult pancreas were noted. The course of the MPD was classified
as descending, sigmoid, vertical and loop, as described by Türkvatan et al.[8] The anatomical patterns of the pancreatic ductal system were classified into six
different types based on the course of the MPD and APD and their openings into the
duodenal wall[8] ([Fig. 1]). The length of the MPD was measured using a measuring tape. The associated variations
of the pancreatic ductal system, like pancreas divisum and ansa pancreatica, were
examined. The pattern of pancreatobiliary union and its opening into the duodenal
wall was studied. The length of the common channel, if the union of the common bile
duct and the MPD was extraduodenal, was measured.
Fig. 1 Schematic diagram showing the different anatomical patterns of the pancreatic ductal
system. Type I – the dominant duct of drainage is the main pancreatic duct, which
opens into the major duodenal papilla, and has an accessory duct communicating with
it, which opens into the minor duodenal papilla; type II - the dominant duct of drainage
is the accessory pancreatic duct, which opens into the minor duodenal papilla and
communicates with the main pancreatic duct, which opens into the major duodenal papilla;
type III - main pancreatic duct with absent/blind accessory duct; type IV - pancreas
divisum; type V - ansa pancreatica; type VI- the accessory duct opens into the minor
duodenal papilla and has no communication with the main pancreatic duct.
For the fetal study, the foot length in millimeters was considered as the reference
for the interpretation of the gestational age in weeks.[9] The presence or absence of the MPD, the APD, the common bile duct, and the major
and minor duodenal papillae were studied.
Radiological Study
For clinical relevance, the same parameters (number and course of the MPD, presence
or absence of an APD, and its communication with the MPD and minor duodenal papilla)
were studied radiologically using MRCP images. Images of clinically-diagnosed chronic
pancreatitis patients, irrespective of their etiology, who underwent MRCP, were obtained
retrospectively from the existing database. Patients with suboptimal imaging and those
with any previous history of pancreatobiliary surgery were excluded from the study.
A total of 103 consecutive patients (67 male and 36 female patients) were selected
and included in the study. The mean age of the patients was 37 years (range: 9–87
years).
The data was statistically analyzed.
Results
Cadaveric Study
In all of the five fetal pancreas specimens, a single MPD was present, which opened
into the major duodenal papilla. As the gestational age increased, the minor duodenal
papilla was identified. The APD was not observed in any of the five specimens ([Table 1]).
Table 1
Pancreatic ducts of the fetal pancreas specimens
|
Foot length (mm)
|
GA/Gender
|
Major duodenal papilla
|
Minor duodenal papilla
|
MPD
|
APD
|
|
55
|
26/F
|
+
|
_
|
+
|
_
|
|
66
|
30/F
|
+
|
_
|
+
|
_
|
|
70
|
32/F
|
+
|
_
|
+
|
_
|
|
78
|
36/F
|
+
|
+
|
+
|
_
|
|
80
|
38/F
|
+
|
+
|
+
|
_
|
Abbreviations: APD, accessory pancreatic duct; F, female; GA, gestational age; MPD,
main pancreatic duct; +/−, present/absent.
In the adults, the major duodenal papilla was present in all of the 15 specimens.
The minor duodenal papilla was present in 11 (73.3%) specimens. The MPD was single,
and had a straight course in 46.7% (7) of the specimens, followed by the descending
course in 40% (6), and the sigmoid course in 13.3% (2) of the specimens. There were
no specimens with vertical and loop courses ([Table 2]) ([Fig. 2a-2c]). The mean length of the MPD was 16.17 ± 1.57 cm. The APD was present in 10 (66.67%)
specimens, and it was blind, disappearing within the substance of the head of the
pancreas and not opening into the duodenal wall.
Table 2
Course of the main pancreatic duct
|
Variables
|
Cadaveric study (n = 15)
|
MRCP study (n = 103)
|
|
Descending
|
6 (40%)
|
80 (77.66%)
|
|
Vertical
|
0
|
10 (9.70%)
|
|
Sigmoid
|
2 (13.3%)
|
13 (12.62%)
|
|
Loop
|
0
|
0
|
|
Straight
|
7 (46.67%)
|
0
|
Abbreviation: MRCP, magnetic resonance cholangiopancreatography.
Fig. 2 Course of the main pancreatic duct in the cadaveric study. (a) Straight; (b) descending; and (c) sigmoid. Abbreviations: D, duodenum; MPD, main pancreatic duct; APD, accessory pancreatic
duct; CBD, common bile duct.
[Table 3] shows that the most common ductal pattern observed in the cadaveric pancreases was
of type III, in which the APD was blind (n = 12; 80%). Ansa pancreatica was observed
in 1 (6.66%) specimen ([Fig. 3a-3c]).
-
The MPD continues as the duct of Wirsung, which is the dominant duct of drainage,
and opens into the major duodenal papilla; the APD communicates with the MPD and opens
into the duodenal wall at the minor duodenal papilla ([Fig. 1])
-
The MPD continues to drain into the minor duodenal papilla through the dominant accessory
duct or duct of Santorini; the duct of Wirsung maintains communication with the dorsal
duct ([Fig. 1])
-
The APD is absent/blind ([Fig. 1])
-
Pancreas divisum: the MPD and APD open into the minor and major duodenal papillae,
and there is no communication between them in the classic subtype of pancreas divisum
([Fig. 1])
-
Ansa pancreatica: the APD is obliterated at its junction with the ventral duct, and
is replaced with an additional curved communicating duct between the ventral and dorsal
ducts at the pancreatic head. ([Fig. 1])
-
The MPD opens into the major duodenal papilla, and the APD opens into the minor duodenal
papilla, but there is no communication between them ([Fig. 1]).
Table 3
Types pancreatic ductal system
|
Types
|
Cadaveric study (n = 15)
|
MRCP study (n = 103)
|
|
I
|
2 (13.3%)
|
26 (25.24%)
|
|
II
|
0
|
4 (3.88%)
|
|
III
|
12 (80%)
|
57 (55.33%)
|
|
IV
|
0
|
8 (7.76%)
|
|
V
|
1 (6.7%)
|
0
|
|
VI
|
0
|
8 (7.76%)
|
Abbreviation: MRCP, magnetic resonance cholangiopancreatography.
Fig. 3 Types of pancreatic ductal system in the cadaveric study. (a) Type I - Dominant duct of drainage is Main pancreatic duct opening into the major
duodenal papilla and has accessory duct communicating with it and opening into the
minor duodenal papilla; (b–i) Type III (Main pancreatic duct with absent accessory duct), (b–ii) Type III (Main pancreatic duct with blind Accessory duct draining uncinate process);
(c) Type V (Ansa pancreatica).
The pancreatobiliary union occurred mostly in the duodenal wall (n = 13; 86.67%),
and it was extra-duodenal in 2 (13.32%) cases. The mean length was 5 mm.
Radiological Study
The APD was observed in all of the 103 MRCP images (100%), and the APD was present
in 45 (43.26%) of them.
The predominant course of the MPD was descending, followed by the sigmoid and vertical
courses ([Table 2]) ([Fig. 4a-4c]). There was no loop course. The APD was absent in 57cases (55.33%)
Fig. 4 Course of the main pancreatic duct in the radiological study. (a) Descending; (b) sigmoid; and (c) vertical. Abbreviations: MPD, main pancreatic duct; CBD, common bile duct, GB, gall
bladder.
Similar to the cadaveric study, the most common duct type observed was type III ([Figs. 5c]). The three subtypes of pancreas divisum (type IV) were noted ([Figs. 5d-i,ii,iii]). Ansa pancreatica (type V) was not observed in the present MRCP study. We have
identified another subtype not described by Türkvatan et al,[8] in which the APD opens into the duodenal wall and ends blindly in the substance
of the pancreatic head without communicating with the MPD, and this has been categorized
as type VI in 8 cases (7.76%). There was no gender difference regarding the course
of the MPD (Chi-squared [χ2] = 4.97; p = 0.083) and the types of pancreatic ductal system (χ2 = 8.93; p = 0.06).
Fig. 5 Types of pancreatic ductal system in the radiological study. (a) Type I - bifid configuration with dominant duct of Wirsung (arrow); (b) type II - bifid configuration with dominant duct of Santorini (arrow) without divisum;
(c) type III - absent duct of Santorini; (d-i) type IV (subtype I): classic pancreas divisum in which there is complete failure
of fusion of the dorsal duct (long yellow arrow) and the ventral duct (short yellow
arrow); (d-ii) type IV (subtype II): main pancreatic duct draining into the minor papilla (long
yellow arrow), and the duct of Wirsung is absent. The distal pancreatic duct in the
tail is beaded with dilated side branches (arrow heads), which is suggestive of chronic
pancreatitis; (d-iii) type IV (subtype III): the main pancreatic duct drains into the minor papilla (long
yellow arrow). The ventral duct of Wirsung (short yellow arrow) is seen communicating
with the dorsal duct through a filamentous communication (thin white arrow). The pancreatic
duct is irregularly dilated (arrow heads) in this patient with chronic pancreatitis;
(e) type VI - duct of Santorini (long arrow) communicating with the minor duodenal papilla
but not with the main pancreatic duct (short arrow).
Discussion
The pancreas is drained by the MPD (duct of Wirsung), which opens into the major duodenal
papilla in the second part of duodenum. It is usually formed from the distal part
of the duct of the dorsal pancreatic bud and the entire duct of the ventral pancreatic
bud. The APD (duct of Santorini) is formed from the proximal part of the duct of the
dorsal pancreatic bud till its opening into the second part of duodenum at the minor
duodenal papilla.[10]
Morphological anomalies of the pancreatobiliary system have been described as one
of the predisposing factors for chronic pancreatitis. Variants of the pancreatic ductal
system like pancreas divisum and ansa pancreatica are mostly incidental findings during
various radiologic procedures, like the ERCP, since the patient might be asymptomatic.
Knowledge about these anatomical patterns of the pancreatic ductal system and its
variants are radiologically important because these might lead to post-ERCP pancreatitis
due to the ductal injury caused during the procedure.[1]
There are a few studies available on the anatomical patterns of the pancreatic ductal
system performed on different populations. Dawson and Langman[2] reported that the MPD was present in all of the specimens in their study on 120
adult pancreas specimens, and Adibelli et al[7] reported the same in their MRCP study of 1,158 chronic pancreatitis patients. The
findings were similar in the present study. While the course of the MPD was straight
in our cadaveric study, the MRCP study revealed that the descending course was the
most common, followed by the sigmoid and vertical courses, which is in accordance
with the studies by Türkvatan et al,[8] Adibelli et al,[7] and Shu et al.[11] The presence of the loop course in the previous studies and its absence in the present
study may indicate that ethnical factors play a role in the prevalence of different
courses of the MPD. In the present study, the mean length of the MPD was 16.17 ± 1.57 cm,
which is similar to the mean of 16.13 ± 3.26 cm reported by Ara et al.[12] Govindraj and Shabna[13] reported a mean length of the MPD of 11.1 cm in the Indian population, a value lower
than that of the present study. Other studies on the mean length of the MPD found
the following values: Kang et al:[14] 17.5 ± 2.8 cm; Kochhar et al:[15] 18.2 ± 3 cm; and Sahni et al:[16] 17.1 ± 1.59 cm in males, and 15.1 ± 1.38 cm in females.
Türkvatan et al[8] classified the pancreatic ductal system into five types, and reported that the most
common type was the MPD (type I) followed by the absent APD (type III). In the present
study, type III was the predominant type, which is similar to the studies by Dawson
and Langman,[2] Sunjida Shahriah et al,[3] Adibelli et al,[7] and Bülow et al.[17] In a literature review on the main anatomical variations of the pancreatic duct
system by Dimitriou et al,[18] a total of 8,260 patients were analyzed. In their study, 94.3% of the cases displayed
normal anatomy (types I-III), 4.5% had pancreas divisum, and 1.2% were reported as
having rare anomalies. Sunjida Shahriah et al[3] reported that type III was the most common type (72.3%) observed, as well as Adibelli
et al,[7] and Bülow et al,[17] who reported prevalences of 63% and 45.6% respectively.
Pancreas divisum (type IV) is a common congenital pancreatic anomaly in which the
dorsal and the ventral pancreatic buds fail to fuse. It is implicated as a cause for
idiopathic chronic pancreatitis.[19] Its incidence has been reported to be of approximately 4–14% of the population.[20] In the present radiological study, it was of 7.76%. The three subtypes of pancreas
divisum were identified in the present MRCP study, which is similar to the findings
of Adibelli et al[7] and Kamisawa and Okamoto.[21] In the present cadaveric study, ansa pancreatica (type V) was observed in one cadaveric
specimen, but not radiologically. It was reported radiologically in the MRCP (1.2%)
by Adibelli et al.[7] Hayashi et al[22] found that it has a significant association with recurrent acute pancreatitis.
In the present radiological study, a type-VI variant was noted where the MPD and APD
open into the major and minor duodenal papillae respectively, with the APD having
no communication with the MPD. Such a variation has been reported earlier.[23] This has been designated as typeVI, and was observed in 7.76% of the cases.
The studies reported different incidences of the APD. Dawson and Langman[2] reported it as 92% in the North American population; Sunjida Shahriah et al,[3] as 27.69% in Bangladesh; and Wilasrusmee and Pongchaicherks,[24] as 57.26% in Thailand. In the present cadaveric study, the incidence was of 66.67%,
and it was of 41.74% in the radiological study. As for the communication of the APD
with the MPD, Dawson and Langman[2] reported a rate of 77.7%, and Sunjida Shahriah et al,[3] a rate of 16.93%. Double, triple and quadruple communications have been reported
in another study.[3] In the present study, no such additional communications were noted.
The patency of the APD was also studied by Dawson and Langman[2] in 20 fetal specimens of gestational age ranging from 13–32 weeks, and in 20 infants
up to the age of 4.5 years. The APD was present and patent in most of the specimens
(95%). It has been shown by Dawson and Langman[2] that obliteration of the APD and minor papilla rarely occurs during fetal life,
which is not in line with the present study, in which the accessory duct was absent
in all of the five fetal pancreas specimens, and the minor duodenal papilla was present
in fetuses closer to term.
The long extraduodenal pancreatobiliary common channel has been considered a predisposing
factor for gall stones and pancreatitis.[2] Dawson and Langman[2] reported an incidence of 26 (52%) male and 21 (46.6%) female cases of common channel
with more than 3 mm in length between the Wirsung duct and the common bile duct. In
the present study, this was observed in 2 cadaveric specimens (13.33%), with a mean
length of 5 mm.
In conclusion, the MPD was observed in every case, and had a predominantly downward
course. The most common pattern of the ductal system was type III. The present study
shows that there are different anatomical types of pancreatic ductal system, which
will be helpful for the hepatopancreatobiliary surgeons and during other procedures,
like the ERCP.
