Keywords
ampullary - biliopancreatic junction - neoplasms - periampullary
Introduction
The ampulla of Vater, also known as the hepato- or biliopancreatic ampulla, was first
described by Vesalius and is named after a German physician: Abraham Vater. It is
the dilated junction of the common bile duct (CBD) and the main pancreatic duct of
Wirsung (MPD) that becomes a common channel before opening into the duodenum at the
major papilla. Although meaning of ampulla is dilated common channel, it is rarely
dilated, and this name is disputed by some investigators.[1]
The ampulla of Vater is surrounded by a group of smooth muscles that forms the sphincter
of Oddi which controls the flow of bile and pancreatic juices into the duodenum. These
smooth muscles also extend to encircle the distal CBD, and the distal MPD. The major
duodenal papilla is located along the medial wall of the second portion of the duodenum.[2]
Given the importance of these anatomic structures, it is essential for radiologists
to understand the basic embryology, normal anatomy, and common variants of ampulla
and periampullary region. Familiarity with the different pathologic conditions involving
this region will improve the diagnostic accuracy of radiologists facing ampullary
abnormalities.
Embryology
Development of the pancreas is like that of other exocrine glands in a way that the
duct appears first and then cells implant around it to create lobules. The endocrine
and exocrine parts of pancreas arise from the endodermal epithelium of the duodenum.
As early as second and third gestational week, the ventral and dorsal ducts grow from
the duodenum.[3] The dorsal bud is larger and located higher than the ventral buds and forms the
superior part of the head, the body, and the tail of the pancreas. Due to the rotation
of the stomach and the duodenum during embryogenesis, the ventral bud moves to the
dorsal direction. At the end of the rotation, the ventral bud is located under and
behind the dorsal bud and forms the inferior part of the head, and the uncinate process
of the pancreas.[4] Each bud has its own independent duct and during the 7th week of gestation, the
two buds fuse.[5] Portion of the dorsal duct in the duodenal segment atrophies, while the rest of
the duct, along with the duct of the ventral bud, forms the pancreatic duct. It joins
the CBD to form the ampulla and drains into the duodenum via the major duodenal papilla
([Fig. 1]). If the duodenal segment of the dorsal bud duct stays patent, it is called the
accessory pancreatic duct that drains in the duodenum through the minor duodenal papilla.[3] If the two buds fail to fuse, it results in pancreas divisum. The close proximity
of the pancreatic bud to the stomach and duodenum can explain the heterotopic pancreatic
tissue in the gastrointestinal tract. Heterotopic pancreas in the pancreaticoduodenal
groove and duodenal wall can result in groove pancreatitis. Annular pancreas is a
rare congenital anomaly resulting from incomplete rotation of the ventral duct, in
which the pancreas forms a ring around the duodenum, which may result in duodenal
atresia in neonates or duodenal obstruction or pancreatitis in adults.[6]
Fig. 1 Normal anatomy of the ampulla is demonstrated on coronal T2-weighted image (A), three-dimensional magnetic resonance cholangiopancreatography image (B), and an illustration (C). Distal common bile duct (solid arrow) joins the pancreatic duct (interrupted arrow)
to form the ampulla. Major papilla is seen (open arrow) as a T2 hypointense structure
(A) and periampullary region is shown in A and C outlined by an elliptical. Target sign is demonstrated in post-contrast arterial
phase axial image D (curvilinear arrow). Embryology of the pancreas is depicted in image E. Image courtesy: Dr. Lokesh Khanna
Normal Anatomy
The ampulla is seen along the medial wall of the duodenum with its length ranging
from 1 to 12 mm (average length of 4.4 mm), and a diameter of 1 to 4 mm (2.6 mm on
average).[7] It is situated in the lower part of the pancreatic head. It protrudes in the medial
aspect of the second portion of the duodenum for a length of 5 to 10 mm to form the
major papilla.[8] Major papilla can also be seen at the junction of the second portion and third portion
of the duodenum.[7]
[9] The ampullary region indicates the distal segments of the CBD and MPD that may or
may not include a common channel ([Fig. 1]). The periampullary region includes the duodenum for a length of 2 cm, the ampulla
of Vater, and the distal most CBD.[2]
The CBD and the MPD may join each other in one of the three different ways:[10]
-
A common channel is formed by joining of the CBD and MPD measuring 1 to 8 mm in length
(60%).
-
Absent common channel but single opening at the papilla with separate opening of CBD
and MPD (38%).
-
In the least common type, there are separate openings in the papilla draining the
CBD and MPD independently (2%).
The minor duodenal papilla is the orifice of the accessory pancreatic duct that is
situated ~2 cm proximal to the major duodenal papilla. It contains terminal portion
of the accessory pancreatic duct surrounded by pancreatic tissue.[11]
The ampulla of Vater is usually seen on computed tomography (CT) or magnetic resonance
imaging (MRI), but physiologic contraction of the sphincter of Oddi can result in
non-visualization.[8] On CT the ampulla is seen as a hypodense structure which shows enhancement after
intravenous contrast similar to the duodenal mucosa even on multiphasic exam. The
normal duodenal papilla is usually less than 10 mm in diameter and the thickness of
the wall of the ampullary part is less than 2 mm.[8] The common channel can be a long (Y shaped) or short type (V-shaped) on magnetic
resonance cholangiopancreatography (MRCP).[12] On T2-weighted imaging, the major papilla and sphincter complex appears as a round,
slightly hypointense structure along the medial wall of the duodenum[12] ([Fig. 1]). Similar to CT, the enhancement of the mucosa in the papilla and ampullary portion
on dynamic imaging is isoenhancing to that of the surrounding duodenal mucosa. According
to an article published by Sun et al target sign was seen in up to 70% of cases.[10] The “target sign” was defined as the appearance produced by an enhancing mucosa
with underlying hypodense ampulla/sphincter complex) of a normal papilla. Morphology
of the papilla could be round, hemispherical, conical, or flat[10] ([Fig. 1]).
Role of Imaging
Conventional imaging including plain abdominal radiographs has low sensitivity in
detecting biliary and pancreatic abnormalities. Incidental findings including pneumobilia,
calcified stone, or pancreatic calcifications may be seen in patients presenting with
abdominal pain.[13]
[14] Fluoroscopy may show duodenal obstruction due to annular pancreas or mass lesion
around ampulla.[15] Many of the ampullary and periampullary abnormalities, including congenital anomalies
and anatomical variants, are first detected on imaging, including CT and or MRI, as
incidental findings in patients being investigated for various clinical problems.
Patients with acquired benign or neoplastic lesions often present with abdominal pain,
obstructive jaundice, and weight loss in case of malignancy. Ultrasound (US) is often
the first modality used to screen patients with upper abdominal pain and jaundice.
It is cost-effective, easily available, and lacks ionizing radiation.[16] On grayscale US, a hypoechoic mass may be seen in periampullary region, along with
intra and extrahepatic biliary and pancreatic ductal dilation.[17] Color doppler is useful in assessing vascular involvement in malignant neoplasms.[18] Metastatic nodes can be detected in peripancreatic and celiac axis and porta hepatis.
It is somewhat limited in evaluating distal CBD and pancreatic duct near the ampulla
and in differentiating benign from malignant lesions.[19] It’s sensitivity to detect liver metastases from ampullary and periampullary neoplasms
has improved with the introduction of contrast enhanced US.[20] US is limited in patients with large body habitus and those with lot of bowel gas.
CT is the commonly used modality in patients presenting with upper abdominal pain including
obstructive biliary symptoms. Use of multidetector technology has improved spatial
resolution due to ability to obtain thinner sections and faster acquisitions reducing
motion artifacts to a minimum.[21] Multiplanar reformats are helpful in detecting tumors and evaluating biliary and
pancreatic ducts in different planes.[22] Use of iodinated contrast has improved visualization of small ampullary and periampullary
neoplasms. It is particularly helpful in staging the disease, detecting perilesional
spread, lymph node metastases and distant spread, most commonly to liver. Multiphasic
CT helps in evaluating relation of tumor to arteries and veins that are essential
for planning the treatment.[23] Patients receiving neoadjuvant chemotherapy need CT for restaging. One important
limitation is radiation exposure, which is of particular concern in younger patients
needing multiple follow-up exams. MRI with its superior soft tissue resolution helps
in detecting small tumors, which is improved by multiparametric imaging including
diffusion weighted and apparent diffusion coefficient map sequences along with dynamic
contrast enhanced imaging.[24] MRCP provides a high-resolution image of ductal system comparable to endoscopic
retrograde cholangiopancreatography (ERCP), in two-dimensional and three-dimensional.[25] MR limited due to longer acquisition time may cause patient discomfort and may not
be performed in some patients including those with claustrophobia, metal pieces in
sensitive location in body, pacemaker, or spinal nerve stimulators. Some of the major
limitations due to patient motion and respiration are being addressed with introduction
of short breath hold acquisitions, use of parallel imaging, and special respiratory
trigger mechanisms.[26] ERCP has been a bedrock for evaluating biliary and pancreatic ductal abnormalities
for a long time, helping in detailed assessment of the anatomy of pancreatico-biliary
ductal system, detecting any normal variants. It is particularly sensitive in detecting
any mural lesions including strictures and intraluminal masses seen as filling defects.[27]
[28] Various therapeutic interventions including sphincterotomy, balloon angioplasty,
stenting, or stone extraction may be performed at the same time.[19] It is limited by being invasive, along with a risk for post procedure pancreatitis.
Endoscopic US (EUS) plays an important role in diagnosing ampullary and periampullary
abnormalities, especially neoplasms.[29] It provides a detailed evaluation of anatomy in that region due to close approximation
of probe to the concerned structures. It has added advantage of obtaining tissue sample
at the time of US.[30] Contrast-enhanced EUS greatly improves the accuracy, helping to differentiate malignant
lesions that are usually hypovascular and help in detecting mural nodules in cystic
lesions.[31] It is limited due to being invasive in nature.
Benign Conditions Affecting Ampulla and Periampullary Region
Benign Conditions Affecting Ampulla and Periampullary Region
Periampullary Duodenal Diverticulum
Duodenal diverticula are diverticula representing extraluminal mucosal outpouchings
devoid of muscle layer. Most (up to 75%) are located in the second part of the duodenum
along the medial wall, adjacent to the ampulla of Vater. When the diverticulum is
within 2 to 3 cm from the ampulla of Vater, it is called periampullary diverticulum.
Diverticulum containing the papilla (intradiverticular papilla) is also named as ampullary
diverticula, whereas diverticulum not containing the papilla is often referred as
juxtapapillary or juxta-ampullary duodenal diverticulum. The incidence increases with
age and the reported incidence is highly variable, depending on the imaging type and
the population, and ranges from 1 to 30%.[32]
[33]
The majority of periampullary diverticula are incidentally found and are asymptomatic,
but occasionally can cause complications. Nonbiliopancreatic complications include
diverticulitis, hemorrhage, perforation or fistula formation. Biliopancreatic complications
include bile duct stone formation, biliary obstruction, cholangitis, and pancreatitis.[34]
[35]
[36] Obstructive jaundice from a periampullary duodenal diverticulum is also known as
Lemmel's syndrome.[37] On fluoroscopic exam after barium ingestion, duodenal diverticulum can be seen as
an outpouching from the medial wall of the second portion of the duodenum. CT and
MRI may show fluid-filled diverticulum along the medial duodenal wall. Sometimes an
air-fluid level is seen at the papillary junction that is easier to detect on CT ([Fig. 2]) and may appear as susceptibility artifact on MRI. Multiplanar reconstructions and
oral contrast can improve the diagnostic yield of CT.[32] At times, a small fluid filled diverticulum can be difficult to differentiate from
an ampullary mass or cyst on imaging.
Fig. 2 Periampullary duodenal diverticulum is seen on axial (A) and coronal (B) contrast enhanced computed tomography as a fluid filled periampullary structure
(solid arrow). Air within the diverticulum (interrupted arrow in A) helps in making accurate diagnosis.
Intraluminal Duodenal Diverticulum
An intraluminal duodenal diverticulum results from incomplete recanalization of the
embryologic foregut. There is a fenestrated membrane within the lumen of the duodenum
and with years of peristalsis affecting the membrane results in the formation of an
intraluminal diverticulum. Although most patients are asymptomatic, a few may experience
abdominal pain, bloating, or fullness. Rarely it can lead to more severe complications
such as gastrointestinal bleeding, and bowel obstruction.[38]
Endoscopy of the duodenum shows two lumens: one is the opening of the diverticulum,
and the other is the duodenal lumen. Imaging diagnosis can be made with barium fluoroscopic
study with classic appearance of contrast filling of the diverticulum surrounded by
radiolucent area that represents the diaphragm which itself is surrounded by contrast
filling the duodenal lumen. This appearance is described as “windsock” or “finger-of-glove.[38] CT usually shows a low-density mass within the lumen of the duodenum representing
the collapsed diverticulum ([Fig. 3]). Oral/intraluminal contrast can help in making accurate diagnosis if there is opacification
of the lumen of the diverticulum.[39] Differential diagnosis includes periampullary neoplasm, intussusception, choledochal
cyst, and duodenal duplication cyst. Duodenal duplication cysts are commonly extraluminal,
located posteromedial to the second portion of the duodenum.[40]
Fig. 3 Intraluminal duodenal diverticulum is demonstrated on contrast-enhanced axial (A) and coronal (B) computed tomography images as a smooth low-density mass within the lumen of duodenum
(arrows).
Ampullary Stenosis
Ampullary stenosis can be defined as the dilation of the CBD and the MPD with laboratory
evidence of biliary obstruction in the absence of a mass or inflammatory lesion at
the ampulla. It can also present with clinical symptoms, such as recurrent abdominal
pain, pancreatitis, and jaundice.[1]
[12]
[41] Dilated CBD and MPD can be easily depicted on CT and MRI; however, it is important
to rule out underlying mass and most patients will need ERCP and EUS or imaging follow-up.
Causes of ampullary stenosis can be sphincter of Oddi dysfunction (SOD), pancreaticobiliary
maljunction, and iatrogenic stenosis.
Sphincter of Oddi Dysfunction
The most common cause of ampullary stenosis is SOD. Prevalence of SOD has been reported
to be up to 15% in the general population.[32] Gold standard for diagnosis of SOD is manometric demonstration of sphincter pressures
>40 mm Hg during ERCP. Endoscopic manometry is, however, an invasive procedure. MRCP
demonstrates dilated MPD and CBD with smooth tapering to the ampulla without calculus
or mass lesion ([Fig. 4]). Secretin-enhanced MRCP can be of added value by demonstrating increase in MPD
diameter of more than 1 mm or prolonged dilatation (>3 mm at 10 minute) in patients
with clinically suspected SOD.[42]
Fig. 4 Three-dimensional magnetic resonance cholangiopancreatography image (A) and T2-weighted coronal image demonstrating dilated common bile duct (solid arrow)
and pancreatic duct (interrupted arrow) with smooth tapering toward the ampulla. Endoscopic
evaluation with manometry showed elevated pressure at the ampulla without mass lesion
that confirmed the diagnosis of sphincter of Oddi dysfunction.
Abnormal Biliopancreatic Junction
Abnormal biliopancreatic junction (ABPJ), also known as pancreaticobiliary maljunction,
is a rare developmental anomaly in which the pancreatic and bile ducts join outside
the duodenal wall, usually forming a long common channel. This anomaly can occur in
isolation or in conjunction with other anomalies such as pancreas divisum and annular
pancreas.[43] Radiologists should be aware of this entity to ensure early diagnosis as ABPJ can
be associated with increased risk of biliary cancer and need close imaging follow-up.[44] In these patients, sphincter of Oddi does not regulate the flow that can lead to
reciprocal reflux between the pancreatic duct and the CBD. This can cause bile stasis
and pancreatitis. Chronic biliary stasis can be the etiology of biliary cancer. ABPJ
can be associated with type I or type IV choledochal cysts.[45]
Morphologically, ABPJ is divided into two broad categories depending upon presence
or absence of CBD dilation. To make a diagnosis of ABPJ, one of the following is needed:
an abnormally long common channel or an abnormal union between the pancreatic and
bile ducts or a PBJ outside the duodenal wall[46]
[47] ([Fig. 5]). There is no consensus on the length of the common channel; however, in the literature,
8 mm to 15 mm length of the common channel has been reported.[48]
Fig. 5 Magnetic resonance cholangiopancreatography image demonstrating biliary pancreatic
junction (solid arrow) outside the duodenal wall with abnormally long common channel
(interrupted arrows).
Various imaging techniques such as MRCP, US, ERCP, or percutaneous or intraoperative
cholangiogram can be used for the diagnosis ABPJ as well as its complications. MRCP
is superior to ERCP in depicting the biliary anatomy[49] ([Fig. 5]). Additionally, secretin enhanced MRCP images can be helpful in functional analysis.
Gadoxetic acid, a hepatobiliary-specific MRI contrast agent, is excreted into the
bile ducts and can be used to demonstrate biliopancreatic reflux in patients with
ABPJ.[50] ERCP can help confirm the lack of effect of the sphincter of Oddi on the ABPJ even
in patients with a relatively short common channel.[51] Important advantages of ERCP are that it allows bile and tissue sampling as well
as biliary intervention. An elevated amylase level in bile suggests reflux of pancreatic
juice through an ABPJ.[47]
Iatrogenic Ampullary Stenosis
Morphologically iatrogenic stenosis can be divided in two subtypes: type I, is when
the stenosis only involves the intraduodenal part of the sphincter complex, and type
II, when the stenosis extends to involve the CBD. Clinical presentation of biliary
obstruction in the presence of history of prior endoscopic or biliary surgery, and
the presence of a biliary dilation in absence of a mass at MRI or CT, without the
evidence of an ampullary mass is concerning for iatrogenic stenosis[41] ([Fig. 6]). Imaging is important to rule out the presence of a mass lesion.[52] Finding that is useful on CT is the size of the papilla: diameter of the papilla
more than 12.3 mm is concerning for malignancy.[53] MR findings of an ampullary mass, papillary bulging, and irregular CBD stricture
are associated with cancer.[32]
Fig. 6 Severe ampullary stricture is demonstrated on three-dimensional magnetic resonance
cholangiopancreatography (A) and postcontrast coronal magnetic resonance images (B) with severe biliary dilation (interrupted arrow) with smooth distal tapering (solid
arrow in A) with uniform enhancement of the ampulla without mass lesion (open arrow
in B).
Ductal Anomalies
Ductal anomalies include pancreas divisum, ABPJ (previously discussed), choledochocele,
and annular pancreas.
Pancreas Divisum
Pancreas divisum is the results when the ventral and dorsal pancreatic ducts fail
to fuse.[54] The ventral duct (duct of Wirsung) drains only the ventral pancreatic tissue into
the major papilla, whereas the majority of the gland empties into the minor papilla
through the dorsal duct (duct of Santorini). There is abnormal proportion of the duct
size and draining enzymes, dorsal duct being smaller in caliber and draining most
of the pancreatic tissue. This may sometimes give rise to santorinicele that is a
focal dilatation of the terminal portion of the dorsal pancreatic duct secondary to
the relative obstruction at the minor papilla[55] ([Fig. 7]). Pancreas divisum is usually asymptomatic but can be associated with patients with
chronic abdominal pain and idiopathic pancreatitis.[56] The diagnosis of pancreas divisum can be made with MRCP, multidetector computed
tomography, and ERCP. Endoscopic retrograde pancreatography shows ventral duct opacification
when standard cannulation of the major papilla is performed. MRCP, on the other hand,
demonstrates noncommunicating dorsal and ventral ducts, independent drainage sites,
and a dominant dorsal pancreatic duct.[49] The ventral duct is typically short and narrow.
Fig. 7 Magnetic resonance cholangiopancreatography image showing nonfusion of the dorsal
(solid arrow) and ventral (interrupted arrow) pancreatic duct suggestive of pancreas
divisum. Focal dilation of the dorsal duct near its insertion to the minor papilla
(open arrow) represents Santorinicele.
Annular Pancreas
Annular pancreas is a rare congenital anomaly in which incomplete rotation of the
ventral anlage leads to a segment of the pancreas encircling the second part of the
duodenum.[57] Annular pancreas has different presentation in adults and children; duodenal obstruction
is the predominant features in children, whereas, pancreatitis is the main presentation
in adults.[58]
Annular pancreas can be diagnosed on the basis of CT and MR imaging findings that
reveal pancreatic tissue and an annular duct encircling the descending duodenum. Pancreatic
tissue appears hyperintense on T1-weighted images, and T2-weighted images and MRCP
can help in identifying the annular duct encircling the duodenum ([Fig. 8]).[58]
Fig. 8 Annular pancreas seen on axial (A) and coronal (B) postcontrast computed tomography images as soft tissue surrounding the duodenum
(solid arrows) with enhancement similar to pancreas. Duct of the annular pancreas
is well demonstrated on magnetic resonance cholangiopancreatography image (interrupted
arrow in C)
Choledochocele
Choledochoceles are cystic dilatations of the distal most (intraduodenal) portion
of the CBD that causes enlargement of the papilla.[1] Classified per Todani classification as type III choledochal cysts, however, they
have distinctive demographic and anatomic features than other types. They also have
lower risk of malignancy than other types of choledochal cysts.[45] Choledochoceles often present at an older age, with an average age at presentation
of 51 years.[59] Clinical presentation is variable with most common presentation being upper abdominal
pain. Most common complication is pancreatitis and other less common complications
include cholestasis, choledocholithiasis, gastric outlet obstruction, and bleeding.
Some researchers believe choledochoceles as a variant of duodenal duplication.[59] Endoscopically it appears as a protrusion of a dilated intramural segment of the
CBD into the duodenum. On sonography, CT or MR imaging, cystic dilation of the duodenal
portion of the distal CBD is seen[60] ([Fig. 9]).
Fig. 9 Cystic dilation of the intraduodenal portion of the common bile duct is shown with
white arrow on greyscale sonographic image (A), T2-weighted axial image(B), postcontrast coronal image (C), and coronal magnetic resonance cholangiopancreatography image (D). Endoscopy image showing smooth bulging papilla (black arrows in E)
Inflammatory Conditions Affecting Ampulla and Periampullary Region
Duodenal Papillitis
Papillitis is an acute inflammation of mucosa overlying major papilla at the junction
of CBD and MPD and can be seen with biliary or pancreatic abnormalities including
cholangitis, pancreatitis, choledocholithiasis, parasitic infestations, or periampullary
diverticulitis.[61] An inflamed papilla is usually enlarged measuring more than 10 mm, hyperenhancing
compared with adjacent duodenal mucosa, which may be homogeneous or striated.[61]
[62] Symmetric wall thickening and hyperenhancement suggest benign papillitis compared
with hypovascular malignant neoplasm.
Groove Pancreatitis
Groove pancreatitis is a rare form of chronic pancreatitis involving a region (groove),
bordered by pancreatic head, duodenum, and CBD.[63] It may be associated with alcohol abuse, smoking, or functional obstruction of minor
papilla.[64] Contrast-enhanced CT and MRI show “sheet like” curvilinear crescentic infiltrating
soft tissue in pancreaticoduodenal groove, showing progressive enhancement on delayed
images.[63]
[65] Additionally, thickening of medial duodenal wall is seen along with cysts within
the wall ([Fig. 10]). On MRI, the soft tissue appears hypointense on T1, variable on T2 weighted images,
showing progressive enhancement on contrast enhanced images. Duodenal wall cysts are
prominently seen on T2-weighted images. MRCP may show distal CBD and pancreatic duct
strictures, widening distance between ampulla and medial duodenal wall and a dilated
“banana shaped” gall bladder.[66] It may be difficult to exclude duodenal or pancreatic malignancy on noninvasive
imaging necessitating an endoscopic US and biopsy and some patients may have to undergo
Whipple’s surgery due to continued suspicion of malignancy.[63]
Fig. 10 Groove pancreatitis is seen as inflammatory changes in the duodenopancreatic groove
with thickened medial wall of the duodenum showing cystic areas.
Periampullary Neoplasms
Periampullary Adenomas
Benign neoplasms arising from the ampulla and the periampullary region are rare, representing
less than 10% of periampullary neoplasms. The most common benign lesions are adenomas.
Ampullary adenomas are glandular dysplastic lesions that arise in and around the duodenal
papilla.[67] Within the duodenum, 10% of all duodenal polyps are ultimately found to be adenomas,
and the most common location is in the periampullary region.[68] Ampullary adenomas are benign lesions but some have considered them to be premalignant
and may possibly progress to carcinoma.[67]
[68] Sixty to ninety percent of adenomas are known to have features of carcinoma especially
in larger lesions.[68]
[69]
Ampullary adenomas may occur sporadically or in the setting of familial adenomatous
polyposis (FAP). Patients with FAP almost invariably develop duodenal adenomas and
have a risk for ampullary carcinoma that is 124-fold greater than the general population.[69] These are often asymptomatic and incidentally discovered on endoscopy. Patients
may present with symptoms related to obstruction of the biliary or pancreatic duct.[69]
Multiple modalities are available for staging of these lesions and to help guide the
most appropriate therapy. Contrast-enhanced CT or MRI show adenomas as a smoothly
marginated, enhancing mass in the periampullary region of the duodenum ([Fig. 11]). Signs of biliary obstruction can also be seen. The role of imaging is to detect
aggressive features such as heterogeneity, ulceration, vascular invasion, and metastasis,
and it also aids in operative planning.[8]
Fig. 11 Periampullary adenoma depicted on axial (A) and coronal (B) contrast-enhanced computed tomography as smooth enhancing mass at the ampulla causing
biliary dilations (black arrow in B).
Cholangiocarcinoma
Cholangiocarcinomas of the extrahepatic duct mostly arise from the proximal one-third
of the duct and distal CBD cholangiocarcinomas account for up to 20% of cases.[70] There is frequent involvement of the periductal nerves and lymphatics.[70] Ninety-five percent of these patients show ductal obstruction at the time of diagnosis.[68] There are three different morphologic subtypes that have different imaging appearances.
These include a mass-forming cholangiocarcinoma, periductal infiltrating cholangiocarcinoma,
and intraductal cholangiocarcinoma. The mass-forming cholangiocarcinoma usually presents
as a discrete lesion that obstructs the extrahepatic bile duct, penetrates the wall,
and invades the periductal tissues. These lesions can show some hypervascularity on
arterial phase images with progressive increased enhancement on delayed images ([Fig. 12]).[68]
[70] There is resultant proximal biliary ductal dilatation to varying degrees.[70] The periductal infiltrating variant is more challenging to identify and may present
as asymmetric and/or concentric ductal wall thickening with associated enhancement
at the site of transition and usually involves a short segment.[68] The thickness of the wall may measure up to 1 cm. The extent of the tumor varies,
ranging from 0.5 to 6 cm in length, sometimes involving all the extrahepatic ducts
and may extend proximally as far as the intrahepatic ducts.[70] On CT or MRI, the thickened bile ducts can be visualized as an enhancing ring or
spot. Periductal-infiltrating cholangiocarcinoma tends to spread along the bile duct
wall via the nerve and perineural tissues toward the porta hepatis. Portions of the
tumor may extend beneath the intact mucosa. The tumor grows longitudinally and extends
along the axis of the bile ducts resembling branches of a tree.[70]
Fig. 12 Mass forming cholangiocarcinoma is seen as enhancing mass on axial (A) and coronal (B) postcontrast computed tomography images (white arrow). Mass (white arrow) is seen
obstructing the bile duct (black arrow) on endoscopic retrograde cholangiopancreatography
image.
The intraductal variant is rare and can have a variable morphology. This subtype is
not readily distinguishable from the other two morphologic subtypes. These lesions
usually spread along the inner surface of the bile duct, either as a superficially
spreading mass, focal wall thickening, or as a discrete intraluminal polypoidal lesion.[68]
Discrete multiple tumors (cholangiocarcinomatosis) may be present along the inner
surface of the bile ducts. This variety is limited to the mucosa and invades the wall
and the surrounding tissue in the very late phase. Intraductal papillary cholangiocarcinoma
is friable and sloughs easily at the time of surgery or endoscopic biopsy. It can
also slough spontaneously and mimic bile duct stones, occluding the bile ducts.[70]
Ampullary Carcinoma
The duodenal papilla is lined by intestinal mucosa, whereas the ampullary portions
are covered by simple mucinous epithelium, as in the normal bile duct, malignancies
of the ampulla can arise from these two cell types. Pancreaticobiliary type of differentiation
is more common than intestinal. Intestinal type is associated with better prognosis.[71]
Ampullary carcinoma is rare, with an incidence rate of 4 to 6 per million. The intestinal
type ampullary carcinoma is relatively more common, and its incidence can increase
200- to 300-fold among genetically susceptible groups such as patients with hereditary
polyposis syndromes. The average age at diagnosis of sporadic ampullary carcinomas
is 60 to 70 years old with patients with an inherited polyposis syndrome presenting
at an earlier age.[71]
The biologic behavior of these tumors depends on the exact organ of origin. Pathologists
divide these tumors into three groups: tumors arising from the duodenal epithelium,
tumors arising from the pancreato-biliary epithelium of the distal CBD or pancreatic
duct, and intra-ampullary tumors showing histologic overlap with combined duodenal
and pancreaticobiliary epithelium.
Intra-ampullary tumors tend to have the best prognosis with relatively earlier presentation
because of early, severe ductal obstruction and a lesser invasive component. Tumors
arising from the pancreatobiliary epithelium tend to have a worse prognosis with prognosis
relatively similar to pancreatic adenocarcinoma.[8] Tumors arising from the duodenal mucosa tend to be large at presentation with a
greater propensity for lymph node metastases. These three subtypes cannot be reliably
distinguished on imaging[68] ([Fig. 13]).
Fig. 13 Ampullary adenocarcinoma arising from duodenal mucosa is shown on axial (A) and sagittal (B) contrast enhanced computed tomography as a large lobulated mass arising from the
periampullary region (arrows).
Ampullary Carcinoid
Isolated ampullary carcinoid tumors are exceedingly rare and are biologically distinct
from other small bowel or duodenal carcinoid tumors, with ampullary carcinoids showing
a higher predilection for metastatic disease. These tumors tend to present as small
lesions, can develop nodal disease even when the primary tumor is quite small, and
almost never present with a hypersecretion syndrome. Given the risk of aggressive
behavior even with small lesions and their tendency to obstruct the biliary tree,
these tumors invariably are treated with a pancreaticoduodenectomy.
Like other neuroendocrine tumors in the bowel or the pancreas, ampullary carcinoid
tumors (and their locoregional lymph node metastases) are isointense to muscle on
T1-weighted images and are either hyper- or isointense to muscle on T2-weighted images[8]
[68]
The most characteristic appearance of carcinoid tumor of the ampulla of Vater is an
avidly enhancing discrete submucosal mass without necrosis or hemorrhage[32]
[72] ([Fig. 14]).
Fig. 14 Periampullary neuroendocrine tumor is seen on coronal contrast-enhanced computed
tomography (A) and axial postcontrast magnetic resonance (MR) image (B) as an avidly enhancing mass that is hyperintense on T2-weighted MR images (C).
Pancreatic Adenocarcinoma
A pancreatic head or uncinate process adenocarcinoma is difficult to differentiate
from a primary ampullary neoplasm. These neoplasms appear to have common imaging findings
and presentation with similar biliary and pancreatic ductal obstruction and relative
hypoenhancement to the surrounding pancreas on imaging ([Fig. 15]). This is especially challenging in the region of the pancreaticoduodenal groove.
Clear differentiation between these two types of lesions is not considered important
given that both are treated with pancreaticoduodenectomy.[68]
Fig. 15 Contrast enhanced axial computed tomography image shows a large necrotic pancreatic
adenocarcinoma arising from the pancreatic head, close to the ampulla.
Periampullary Duodenal Adenocarcinomas
Adenocarcinoma represents up to 80 to 90% of all primary duodenal malignant tumors.
It is predominantly located in the second portion of the duodenum. Fifty percent of
patients present with metastasis at the time of diagnosis. The presenting symptoms
are bleeding, anemia, obstructive jaundice, or duodenal obstruction with vomiting.[73] Clinical presentation including pancreatic and biliary ductal obstruction is similar,
but their biologic behavior tends to be different. On CT and MR imaging, duodenal
adenocarcinoma may present as a soft-tissue/ polypoid mass, a concentric or asymmetric
thickening, an annular narrowing with irregular borders or as an ulcerated mass.[8]
[68] Ulceration is strongly indicative of the diagnosis of adenocarcinoma and is well
visualized on CT and MR imaging. Mild, heterogeneous late enhancement after IV contrast
is seen may be seen because of a predominant fibrous component. Lymph node enlargement
is often absent contrary to other tumors such as duodenal lymphoma.[73]
Differentiating Benign and Malignant Biliary Stricture on Imaging
One of the important challenges of MRCP is to differentiate a benign versus malignant
stricture. Several studies have shown malignant strictures to be more common in males
compared with females.[74]
[75] Benign strictures are commonly related to prior cholecystectomy, inflammation, or
pancreatitis.[74] Patients with primary sclerosing cholangitis or autoimmune disease may show multiple
strictures.[76] Benign strictures are usually short segment with smooth margins and show symmetric
dilation of biliary radicals.[74]
[75]
[76] Malignant strictures on the other hand tend to be longer, irregular, and thicker
due to infiltrative growth of cancer, with indistinct margins and showing increased
enhancement relative to liver parenchyma on portal venous phase.[74]
[75]
[77]
[78] There is asymmetric upstream biliary ductal dilation in malignant strictures. Presence
of mass is highly specific for a malignant stricture; however, its nonvisualization
does not exclude the possibility.[74]
Conclusion
The ampulla of Vater is an anatomically complex region and is a site of wide range
of anomalies and pathologies. Many times presentations can be nonspecific. Noninvasive
imaging, especially, MDCT and MRCP, can detect these lesions and at times provide
accurate diagnosis with better understanding of the anatomy, embryology, and pathophysiology.
A summary of lesions affecting ampullary and periampullary region is provided in [Table 1].
Table 1
A summary of lesions affecting ampullary and periampullary region
|
Type of abnormality
|
Clinical
|
Imaging
|
|
Congenital
|
|
Periampullary Duodenal Diverticulum
|
Outpouchings along medial wall of duodenum within 2-3 cm of ampulla of Vater Incidental
findings on CT or MR Complications: diverticulitis, hemorrhage, perforation or fistula
formation, stone formation, biliary obstruction (Lemmel syndrome), cholangitis, and
pancreatitis.
|
CT and MR fluid-filled outpouching along the medial duodenal wall, may have air fluid
level seen as susceptibility artifact on MRI.
Improved visualization with MPR reconstructions and oral contrast
|
|
Intraluminal Duodenal Diverticulum
|
Result of incomplete recanalization of embryonic foregut. Usually, asymptomatic.
Rarely can cause abdominal pain and present with GI bleed or obstruction Endoscopy:
dual lumens seen.
|
Fluoroscopy: Contrast filled diverticulum surrounded by radiolucency representing
diaphragm, and outermost layer of contrast in duodenum (Windsock/finger in glove sign)
CT: Hypodense mass in duodenum.
|
|
Abnormal biliopancreatic Junction (pancreaticobiliary maljunction)
|
Rare developmental anomaly.
Pancreatic and bile ducts join outside the duodenal wall, forming long common channel.
Increased risk of biliary cancer.Need close imaging follow-up.
ERCP provides anatomical information, assess sphincter of Oddi function and bile sampling.
ERCP provides anatomical information, assess sphincter of Oddi function and bile sampling.
|
MRCP with secretin - Depicts biliary anatomy and provides functional information.
MRI with hepatobiliary contrast (Gadoxetic acid)- can show biliopancreatic reflux.
|
|
Pancreatic divisum
|
Failure of fusion of ventral and dorsal pancreatic ducts.
Can present as idiopathic pancreatitis.
ERCP show ventral duct opacification with cannulation of the major papilla.
|
MRCP show dorsal and ventral ducts opening separately in minor and major papilla respectively.
|
|
Annular Pancreas
|
Rare congenital anomaly A part of pancreas encircles second part of duodenum. Can
present as duodenal obstruction (children) and pancreatitis (adults).
|
CT/MRI: Pancreatic tissue seen surrounding the second part of duodenum.
MRCP: Pancreatic duct seen encircling the duodenum.
|
|
Choledochocele
|
Cystic dilation of intraduodenal portion of CBD resulting in enlarged papilla (type
III choledochal cyst).
Can present as abdominal pain cholestasis, choledocholithiasis, gastric outlet obstruction
and bleeding.
|
CT/MR: Cystic dilation of intraduodenal portion of distal CBD.
|
|
Acquired
|
|
Ampullary Stenosis
|
Characterized by dilated CBD and MPD with laboratory evidence of biliary obstruction
in the absence of a mass or inflammatory lesion at the ampulla.
Can present with recurrent abdominal pain, pancreatitis, and jaundice.
|
CT and MRI/MRCP: Dilated CBD and MPD.
Careful attention to rule out underlying mass
|
|
Sphincter of Oddi Dysfunction (SOD)
|
Inability of the sphincter to contract and relax in a normal way.
May cause biliary obstruction, presenting with abdominal pain and pancreatitis.
Gold standard for diagnosis: Manometric demonstration of sphincter pressures >40 mmHg
during ERCP.
|
MRCP: Dilated MPD and CBD with smooth tapering to the ampulla without calculus or
mass lesion.
Secretin-enhanced MRCP demonstrates increase in MPD diameter of more than 1 mm or
prolonged dilatation (>3 mm at 10 min)
|
|
Iatrogenic ampullary stenosis
|
Narrowing of sphincteric complex in presence of prior biliary intervention or endoscopy.
|
MRI and CT: Biliary dilation in absence of obstructing ampullary mass.
|
|
Neoplasms
|
|
Benign
|
|
Periampullary adenomas
|
Benign lesions in and around ampulla.
May have features of carcinoma in larger lesions, especially those with FAP.
May present with biliary obstruction.
|
CT and MRI: Smooth enhancing mass in periampullary region.
Biliary dilation Signs of malignancy- heterogeneity, ulceration, vascular invasion,
and metastasis.
|
|
Malignant
|
|
Cholangiocarcinoma (CCA)
|
Can be mass like, infiltrating or intraductal.
Present with obstructive jaundice.
|
CT and MRI: Depending upon tumor type.
Mass forming- Heterogenous lesion showing progressive enhancement and biliary dilation.
Periductal infiltrating- segmental enhancement and wall thickening, spreading along
bile duct branches.
Intraductal (rare)- intraluminal polyp or superficial spreading mass.
|
|
Ampullary Carcinoma
|
Mass lesions arising at ampulla.
Intestinal or pancreatobiliary type.
Seen with increased frequency in hereditary polyposis syndromes.
|
CT and MRI — Enhancing mass may be seen at ampulla with dilated bile and pancreatic
ducts.
|
|
Ampullary carcinoid
|
Rare aggressive neoplasms present with metastases even when small.
Usually, nonfunctioning.
Cause biliary obstruction.
|
CT and MRI: Enhancing mass without necrosis or hemorrhage.
|
|
Pancreatic adenocarcinoma
|
Mass in pancreatic head presenting with abdominal pain and obstructive jaundice.
|
CT and MRI: present as a hypo enhancing mass in head of pancreas
MRCP: CBD and pancreatic ductal dilation (double duct sign)
|
|
Periampullary Duodenal adenocarcinomas
|
Majority of primary duodenal malignant tumors present with bleeding, anemia, obstructive
jaundice or duodenal obstruction with vomiting.
|
CT and MRI: polypoid soft tissue mass causing concentric or asymmetric narrowing of
duodenal lumen. Ulceration strongly supports diagnosis of duodenal adenocarcinoma.
|
