Keywords ultrasound measurements - reference values - pancreas - guideline - student
Introduction
Why and when should pancreatic measurements be carried out? Normal values are used
to
detect deviations. Subjective impressions can be viewed objectively. Common
indications for ultrasound of the pancreas are upper abdominal complaints,
lipasemia, initial diagnosis, worsening of diabetes mellitus, acute and chronic
pancreatitis, exocrine pancreatic insufficiency, obstructive jaundice, and other
reasons for suspecting tumors. The measurements detect focal or generalized organ
enlargement and can be used as baseline measurements for subsequent scans. Different
examiners can also carry these out at various times. For example, the measurements
are part of the follow-up checks and treatment decisions for autoimmune pancreatitis
under cortisone therapy. In routine clinical practice, exocrine pancreatic
insufficiency is a common laboratory finding that has to be matched with imaging to
make treatment decisions. It is not only pancreatic diseases such as chronic
pancreatitis, autoimmune pancreatitis, or cystic fibrosis that lead to exocrine
pancreatic insufficiency. The natural pancreatic aging process is characterized by
lipomatosis and fibrosis and may result in parenchymal atrophy and exocrine
insufficiency [1 ]
[2 ].
Main pancreatic duct (MPD) dilatation is associated with different pathologies that
need to be assessed in conjunction with the patient’s history, examination, and
other findings such as pancreatic duct stones or calcification. It is one of the
criteria for the diagnosis of chronic pancreatitis. It is rarely associated with
intraductal papillary mucinous neoplasia of the main duct type, while MPD dilatation
with downstream ductal stricture may indicate a malignant tumor. Minor dilatation
of
the MPD also occurs in older people in the context of parenchymal atrophy, MPD
requires diagnostic clarification to detect a malignant tumor at an early stage
[3 ].
It is not necessary to measure the pancreas in every patient. However, one should
know the normal values to diagnose pathological deviations and disease criteria. It
is vital to measure correctly, and this requires correct sonographic imaging of the
pancreas.
In general, measurements allow the comparison of unknown quantities, e. g., an
organʼs length, width, thickness, and volume, with normal values or, in other words,
known quantities [4 ]. These results allow
quantitative statements on the diameters of an organ, duct, vessel, or any anatomic
structure [5 ]
[6 ]
[7 ]. However, the measured values
should not be seen in isolation but in the overall context of the clinical question,
the patient’s history, laboratory values, and findings in the other organ
systems.
Image storage and documentation of measurements and normal findings should be part
of
quality assurance in imaging.
Aim
This paper aims to review the published literature and provide current knowledge of
sonographic measurements and reference values of the pancreas, including limitations
and pitfalls. In addition, the connection between ultrasound examination technique
and reliable measurements, the influence of age, gender, constitution, ethnicity and
other variables, the comparison of ultrasound measurements to measurements using
other imaging techniques, and the clinical relevance of measurements are analyzed
and illustrated. A comprehensive clinical evaluation should describe the pancreatic
size and volume, pancreatic duct diameter, echogenicity, and elastographic
properties. A selection of ultrasound measurements for the daily routine is given,
together with practical advice on how to use them. In addition, anatomical and
congenital variations and their possible clinical implications are summarized.
Material and Literature Review Methods
Material and Literature Review Methods
Three papers published in German journals between 2010 and 2012 reported the normal
sonographic values for abdominal sonography [5 ]
[6 ]
[7 ]. An analysis of scientific literature
published from 2011 to 2023 on reference values in pancreatic ultrasound was
conducted for the current narrative review.
Search strategy
PubMed was searched for entries from 01/01/2011 to 17/02/2024 using the following
keywords and binary operators: Pancreas AND (ultrasound OR ultrasonography OR
sonography) AND (measurement OR sizing OR diameter OR width OR height OR length
OR “reference value” OR “normative value” OR “cut-off value”). 2311 entries were
identified in PubMed (final search date: 17.2.2024).
Study selection
Two of the authors independently reviewed titles and abstracts for eligibility.
Animal studies, studies related only to pediatric cohorts (0–14 years), case
studies (<10 cases), editorials, letters to the editors, articles without
English, German, French, or Spanish text, duplicates and articles referring not
to the pancreas, articles including only measurements of pathologic conditions
of the pancreas and articles only including non-ultrasound imaging modalities
were excluded. Articles already included in the reference list of the review on
reference values in biliopancreatic ultrasound published in 2011 [6 ]
[8 ]
[9 ]
[10 ]
[11 ]
[12 ]
[13 ]
[14 ]
[15 ]
[16 ]
[17 ]
[18 ]
[19 ]
[20 ]
[21 ]
[22 ]
[23 ]
[24 ]
[25 ]
[26 ]
[27 ]
[28 ]
[29 ]
[30 ]
[31 ]
[32 ] were separately evaluated and partly included as the review was
initially published in German only. Extensive crosschecking of the reference
list of the retrieved articles was also performed. Disagreements regarding
eligibility were resolved by discussion and consensus among all authors.
Data extraction
Data were extracted for the year of publication and imaging method used for
pancreatic assessment (e. g., transabdominal ultrasound, endoscopic ultrasound,
CT, MRI, shear wave elastography). Furthermore, data were sorted by selected
pancreatic parameters (e. g., size, volume, pancreatic duct, fat content). For
search results, see the flowchart [Fig.
1 ].
Fig. 1 Flowchart describing search strategy and selection of
studies included in this review. *other reasons, e.g. same study
population with follow-up, selection of most recent study version of
same clinical question, same review topic. **further important
references were included from 2010 and earlier according to the review
by Sienz et al. and if very recently published during the last weeks and
with important content.
Examination technique
Prerequisites for measurement (e. g., transducer type and frequency, position
of the patient)
Patient preparation
The planned examination should preferably be performed under fasting
conditions, as food residues in the stomach may lead to artifacts
limiting the sonographic assessment of the pancreas. Regardless, the
advantage of an ultrasound examination is that it can be carried out
at any time, especially in acute situations. However, better results
are achieved under fasting conditions (usually 4 to 6 hours, under
study conditions often up to 8 hours).
Drinking 500–700 ml of water 10–15 min. before examination can be
considered.
Patient positions
Transducer type and initial transducer position
Standard abdomen 2–7 MHz multifrequency curvilinear probe, positioned
in the epigastric triangle directly below the sternum (subcostally
and subxiphoidally) for the pancreatic head, body, and parts of the
tail [Fig. 2 ]
[3 ]
[4 ] and an intercostal probe
position in the 10th to 11th intercostal space for the left lateral
parts of the pancreatic tail [Fig.
5 ].
Fig. 2 The pancreas head is imaged in the transverse section
and appears uniformly normal in size. L: Liver. ST: Stomach. AGD:
Superior gastroduodenal artery. DUO: Duodenum. IVC: Inferior vena
cava. AO: Aorta. C: Confluens (portal vein).
Fig. 3 In the right upper abdomen, with a transducer position
slightly more caudal than for the pancreatic corpus, the normal
pancreatic head is imaged. Longitudinal section with craniocaudal
(60 mm) and anteroposterior measurements (28 mm). The liver,
stomach, and spine are indicated. PH: Pancreatic head. IVC: Inferior
vena cava. PV: portal vein. HA: Hepatic artery.
Fig. 4 The pancreas body is measured over the superior
mesenteric artery region from the leading edge to the trailing
edge.
Fig. 5 In the splenic hilus, the pancreas tail is measured
from the anterior edge to the posterior edge.
Ultrasound examination workflow and criteria
As a rule, the body of the pancreas is first shown in a cross-section over the
splenic vein and superior mesenteric artery. To assess the head of the pancreas,
the transducer is moved slightly clockwise to the patientʼs right and tilted
caudally.
Visibility of the pancreas may be improved by repeat dosed compression with the
US probe while the patient is breathing in and out and/or when the patient
bulges out their abdomen. For mobile patients, better visualization can be
attempted while standing [Fig. 2 ]
[3 ]
[4 ]
[5 ]
[Table 1 ].
Table 1 What should you do when learning and performing
ultrasound?
Anatomical structure
What should I do?
Pancreatic body
In the supine position, the pancreatic body is imaged in a
transverse section. The standard section shows the splenic
vein and the superior mesenteric artery.
The pancreatic body is measured from the ventral
contour to the dorsal contour.
In the pancreatic body, the pancreatic duct is
routinely assessed. The inside diameter is
measured.
Note:
The pancreas is easier to see when the abdomen is
bulged out.
In mobile patients, the pancreas can also be examined
while standing.
Drinking still water can improve visibility in the
case of disturbing gas in the stomach
Pancreatic head
After examining the pancreatic body, the transducer is moved
slightly clockwise to the patientʼs right and tilted
caudally in the transverse section, and the pancreatic head
is adjusted.
In this position, the transducer is rotated into the
longitudinal section.
The anteroposterior and transverse diameters are
measured.
Pancreatic tail
The tail of the pancreas is located intercostally in the
splenic hilum. When locating the tail of the pancreas, it is
helpful to target the splenic vein, as this forms the dorsal
border of the tail of the pancreas.
The tail of the pancreas is measured from the
anterior to the posterior contour or along its
orthogonal axis.
Attention is paid to whether the tail of the pancreas
can be seen and whether it is enlarged. In this
case, it is measured.
Due to the retroperitoneal location and proximity to ultrasound-reflecting
structures (e. g., gas in the digestive tract), complete sonographic examination
is often challenging. This is particularly true for the pancreatic tail. A
previous Japanese study tried to quantify the possible “blind area” in
ultrasound visualization of the pancreatic tail [33 ]. They investigated 39 patients using ultrasound with GPS-like
technology and fusion imaging with CT. The real unobservable length of the
pancreatic tail was estimated to be approximately 4 cm, accounting for
approximately 25% of the real pancreatic length (mean 16 cm in this study).
Using the intercostal approach, complete visualization of the pancreatic tail
was possible only in 33% of patients [33 ].
Another study reported incomplete pancreatic tail visualization in 32% of cases
[34 ]. Therefore, it is crucial to
realize the possible limitations of transabdominal ultrasound with respect to
visualizing the whole pancreatic tail.
Nakao et al. [35 ] published a protocol for
better visualization of the whole pancreatic organ that entails positioning the
patient in a sitting position, having the patient drink 350 ml of liquid (mostly
tea), and then waiting for the patient’s stomach to fill in order to eliminate
disturbing gas. By using this “special pancreatic ultrasonography” and taking
more than 20 minutes for every investigation, they achieved a significantly
higher sensitivity (92%) compared to routine ultrasound (70%) for detecting
cysts (447 cysts in 186 patients). The improvement in cyst detection was
significant for all parts of the pancreas but was more evident for the
pancreatic head (97% vs. 70%) and tail (67% vs. 27%) compared to the body,
body-tail, and uncinate process [35 ]. In
our experience, visualization of the tail of the pancreas depends mainly on the
examinerʼs experience. In order to achieve the most complete assessment of the
pancreas, the examination should be carried out in the supine, left and right
lateral, and standing positions. If qualitatively adequate and complete
sonographic visualization of the pancreas is not achieved despite an adequate
preparation and examination technique by an experienced examiner, a decision
must be made as to whether to perform radiological cross-sectional imaging or
endosonography, depending on the indication for the examination.
When assessing the pancreas, the size of the different parts (head, body, and
tail) and their harmonic relation, contour, echogenicity of the pancreatic
parenchyma, and the diameter of the pancreatic duct are evaluated [6 ].
Complete assessment of the whole pancreatic organ is essential for detecting and
excluding a pancreatic pathology. Particular attention should be directed to
ductal changes, which may be the result of aging processes of the parenchyma
[1 ]
[3 ] as well as early signs of chronic pancreatitis and especially
neoplastic pancreatic lesions, including pancreatic ductal adenocarcinoma (PDAC)
and its important differential diagnoses [36 ]
[37 ]
[38 ]
[39 ]
[40 ].
Pancreatic size and volume
Pancreatic size and volume
The head of the pancreas is imaged in transverse and longitudinal sections. The
transverse diameter and the anteroposterior diameter are measured at the head of the
pancreas in its largest dimensions [6 ]
[41 ]
[42 ]
[43 ]
[44 ]
[45 ]
[46 ]. The pancreatic body is
viewed in a transverse section. The most reproducible and, therefore, reliable point
is measured at the level of the superior mesenteric artery anteroposterior from the
ventral to the dorsal contour [6 ]
[42 ]
[43 ]
[45 ]. For the tail, the maximal
orthogonal diameter is evaluated with the probe in the 10th to
11th intercostal space in the anterior axillary line [6 ]
[13 ]
[42 ]
[43 ]
[45 ].
Treiber et al. conducted a retrospective study establishing reference values for the
pancreatic head, body, and tail based on 921 patients (443 males, 478 females, aged
41±13 years old) without pancreatic disease. The pancreatic head and body were
measured from ventral to dorsal, and the tail was measured perpendicular to the main
axis of the pancreas. Normal values (5th and 95th percentile)
were 2.2±0.49 cm (1.5–3.1) for the head, 1.1±0.32 cm (0.6–1.6 cm) for the body, and
2.1±0.49 cm (1.4–3.0) for the tail. The craniocaudal diameter was not reported. Body
height, weight, and BMI were positively correlated with pancreatic size, whereas age
only showed a significant correlation with the pancreatic head and body size.
Patients with chronic pancreatitis showed slightly but significantly larger
measurements than the average population. Mean differences were 3 mm at the head,
3
(male) respectively, 4 (female) mm at the body, and 2 mm at the tail. They concluded
that despite a statistically significantly enlarged pancreas size in chronic
pancreatitis, the mean absolute values were still 5–95% percentile in healthy
adults. Therefore, the clinical value of pancreatic measurement for the
differentiation of healthy or pathologic conditions remains unclear [42 ].
In the study by Pirri et al., 77 healthy subjects (25 males and 52 females, 56±18
years) were analyzed regarding the biliopancreatic system. Patients were examined
in
a supine and left lateral decubitus position in epigastric longitudinal orientation,
measuring the craniocaudal and anteroposterior pancreatic head diameter, and in
transverse orientation, measuring the right-left and anteroposterior diameters. A
mean value of 49±10 mm [26–77] mm (mean±SD [minimum-maximum] for the cranio-caudal
pancreatic head diameter was found [41 ]. The
antero-posterior diameter in a supine position was 23±5.5 mm in females and
25±5.3 mm in males.
A prospective study with 16 asymptomatic volunteers (8 males, 8 females; age 21±2
years) was performed with a 1–5 MHz convex probe to evaluate sizes and to determine
elasticity. The images were obtained with patients in a supine position in a
transverse or slightly oblique transverse plane. Dimensions of the pancreatic head,
body, and tail were recorded. The mean dimensions were reported as follows: 17±3 mm
for the head, 14±4 mm for the body, and 14±6 mm for the tail, with a significant
correlation with age, height, and weight [47 ].
The study by Almutairi showed smaller pancreas dimensions for all three segments,
therefore calling into question the existence of an established measurement method
between different studies.
Khammas et al. aimed to determine baseline values in Malaysian adults. 408
participants were analyzed with abdominal US, and 294 were classified as normal.
After an 8-hour fasting period, participants were positioned in a supine or lateral
decubitus position. A 3.5 MHz probe was used. Measurements were taken using a high
epigastric probe position in the antero-posterior direction. Values of 2.62±0.53 cm
for the head and 1.61±0.49 cm for the body were measured. Due to the difficulty in
assessing the pancreatic tail on the transverse scan, this study did not measure it.
Increased diameters were found in patients with hepatobiliary disease [46 ].
In a Nigerian cohort, pancreatic measurements were performed to compare 150 diabetic
and 150 matched non-diabetic persons [48 ].
They reported an anterior-posterior head diameter of 2.32±0.22 cm, body diameter of
1.43±0.19 cm, and tail diameter of 1.34±0.20 cm in the non-diabetic controls.
In transverse computed tomography (CT) and magnetic resonance imaging (MRI)
examinations, determination of the anterior-posterior and lateral diameters is
considered standard [49 ], and the craniocaudal
diameter is often neglected since it is only illustrated by reconstruction. One
study showed a significant discrepancy between MRI and US measurements with smaller
sizes using ultrasound for each pancreatic segment ranging from 14.4–43.3% compared
to MRI [43 ]. As has been shown by a study
including measurement of the cranio-caudal pancreatic head diameter [41 ] and a comparison of measurements performed
on US and MRI [43 ]: “The pancreatic head is
larger than often assumed” [41 ].
Factors influencing interpretation
Physiological aging processes of the pancreas with initially focal and later
during aging diffuse changes have to be differentiated from irreversible chronic
inflammation and fibrosis [1 ]
[3 ]
[19 ]. An increase in diameter with inspiration has also been stated
[50 ]. This may partly explain
differences between measurement results of ultrasound and cross-sectional
imaging methods carried out under more extended breath-holding inspiration
maneuvers.
The influence of age [20 ]
[25 ]
[29 ]
[30 ]
[32 ] and gender [25 ]
[46 ] on pancreatic size has been discussed in the literature. The
organ size of the pancreas correlates to some degree with body weight and height
[29 ]
[51 ]. A positive correlation of pancreatic size with diabetes mellitus
type 2 (DM) was shown, whereas a negative correlation with DM type 1 was
demonstrated [9 ]
[29 ]
[48 ]
[52 ]. However, conflicting
results with a negative correlation with diabetes type 2 were shown in a
Nigerian study [48 ]. The longer duration
of diabetes mellitus was associated with smaller pancreas body and tail
dimensions, while pancreas head dimension was not significantly affected by the
duration of illness [48 ]. The pancreas
enlarges in inflammatory diseases, including acute and chronic pancreatitis and
neoplastic infiltration [42 ]. In patients
with cystic fibrosis, the corpus and cauda may show atrophy with an enlarged
pancreatic head with strong echogenicity [13 ]. The pancreatic size has also been described as smaller in
protein deficiency syndrome, marasmus, and Kwashiorkor [29 ]. In summary, most studies state a
larger pancreatic size in men than women and a decrease in pancreatic size
during aging. However, no significant correlation between aging and sex was
demonstrated in diabetics [48 ].
Reference values and documentation
Pancreatic head:
49±10 (26–77) mm in (longitudinal plane, cranio-caudal measurement) [6 ]
[41 ].
34±8 (19–52) mm (right-left diameter) [6 ]
[41 ].
23±5 (14–39) mm (antero-posterior diameter) [6 ]
[41 ]
[45 ].
Corpus: 10–20 mm [6 ]
[13 ]
[45 ].
Cauda: 20–35 mm [6 ]
[13 ]
[45 ].
The size of the pancreatic head should be documented in at least two diameters.
We recommend the documentation of all three dimensions reflecting examination
quality. However, the benefit of absolute size measurements in the clinical
routine remains an open issue.
Pancreatic Duct
The pancreatic duct should be identified and measured in all (mobile) patients. If
this is not possible in the supine position, the examination should also be
performed in the left lateral and standing positions [Fig. 6 ]
[7 ]. The maximum diameter is measured from the inner-to-inner layer in the
corpus and should be less than 2 mm [45 ]. The
values in the pancreatic neck (between head and corpus) may be physiologically
larger than 2 mm [19 ]. An increase in
pancreatic duct diameter with aging was also demonstrated [3 ]
[17 ].
It is essential to know that the diameter of the pancreatic duct will increase in
about 50% of healthy subjects when changing the position from supine to upright
[53 ] and during inspiration [50 ] and secretin stimulation as used in
magnetic resonance imaging (MRCP) of the pancreatic duct and rarely also in
endoscopic retrograde cholangio-pancreaticography (ERCP) [54 ]
[55 ].
However, pharmaceutical secretin preparations are no longer available on the market.
Endosonographically, the Ductus Wirsungianus can be visualized regularly. The
average diameter of the normal MPD was 1.7 mm, with an interquartile range of
0.9–4.3 mm [34 ]. In an MRI study, Wang et al.
describe the diameter of the pancreatic duct in the pancreatic body as 1.57±0.35 mm,
with an age-related increase [56 ]. Beyer et
al. described the average width of the pancreatic duct on MRI as 1.8±0.96 mm [57 ].
Fig. 6 The pancreatic duct is measured in the pancreas body near the
pancreas head, and the measurement is performed at the inner contours (a,
b).
Fig. 7 Slightly hyperechoic pancreas with slightly less echogenic
ventral attachment to the pancreatic head and well visible, very narrow
pancreatic duct. The course of the pancreatic duct is marked by the
measurements.
Interestingly, the pancreatic duct was slightly wider after cholecystectomy:
2.1±1.09 mm. This study also described an increase in the width of the pancreatic
duct as part of the aging process. The authors considered a duct width of up to 3 mm
normal in people up to 65 years of age and up to 4 mm in people over 65 [57 ].
Reference values and documentation
Pancreatic body:<2 mm (age-dependent>50 years old up to 2.5 mm).
Upper limit values in the pancreatic head, especially in the neck between the
caput and corpus, may be up to 3 mm.
The diameter of the pancreatic duct should be measured in the pancreatic body in
all patients with corresponding clinical questions. Consequently, the report
should also mention if the pancreatic duct cannot be visualized.
Practical tips, tricks, and recommendations
A review analyzing pancreatic duct imaging during aging was recently conducted
[3 ]. The consensus of the pancreatic
duct diameter of 3–2–1 mm for the head, body, and tail was further strengthened.
Aging can lead to slight pancreatic duct dilatation without pathologic
significance. However, a slight dilatation of the pancreatic duct may be
associated with pancreatic pathology (early signs of PDAC) in nearly one-fourth
of individuals [58 ]. The following
age-adjusted reference values can be recommended: upper normal limit 2 mm for
people<50 years and 2.5 mm for people>50 years. In patients with a
pancreatic duct diameter of>2 mm measured in the pancreatic body in a supine
position, an underlying (obstructive) pathology, especially PDAC, needs to be
excluded [3 ]. In geriatric [59 ]
[60 ], palliative care [61 ]
[62 ], and non-mobile patients in emergency
care [63 ]
[64 ], different questions need to be answered rather than measuring
organ diameters, which are related to the specific conditions, complications of
pancreatitis, and other pathologies [65 ]
[66 ]
[67 ]
[68 ].
Factors influencing interpretation
An increase in pancreatic duct size with aging was demonstrated [3 ]
[17 ], and changes in diameter during changes of position, e. g., wider
in upright body position compared to supine, were shown [53 ].
Echogenicity
With the aging process, the parenchymal volume decreases, and fatty infiltration
occurs. Focal areas of multiple fatty infiltration are hyperechoic and must be
differentiated from pathological changes [1 ].
An increase in the echogenicity of the pancreatic parenchyma is shown with age [1 ]
[3 ]
[17 ]
[32 ], whereas the BMIʼs influence on
echogenicity remains controversial. Knowing that body weight usually increases
during aging, such a correlation between BMI and echogenicity seems logical [25 ]
[29 ]
[32 ]. The pancreatic
echogenicity can be compared to healthy liver parenchyma [69 ]
[70 ].
Graduation of pancreatic echogenicity in comparison to the healthy liver parenchyma
has been proposed by Marks et al. [69 ] and
Worthen and Beabeau [70 ]. However, this method
is very subjective, especially in obese patients or subjects with hepatic diseases
where alterations in the liver parenchyma are present. This comparison is not
generally recommended due to significant variations during aging and the high
prevalence of pancreas and liver metabolic changes.
A Korean study retrospectively calculated the pancreato-perihepatic fat index for
286
patients [71 ]. This fat index was
significantly higher in subjects with metabolic syndrome and was strongly associated
with waist circumference.
In the literature, two parts of the pancreatic headʼs “normal” echogenicity are
described [72 ]. A demarcated hypoechoic area
within the pancreatic head compared to the rest of the pancreas can often be
observed in younger and healthy (more often in female) subjects correlating to the
embryological ventral portion [Fig. 8 ]
[72 ]. Two different embryologic origins
explain the feature. A prevalence of 28% in an ultrasound study among 32 healthy
volunteers has been published [73 ]. A 22%
prevalence of hypodense portions of the head is stated for CT examinations [74 ]. Another CT study revealed a 3.2%
prevalence of uneven fatty infiltration that has to be differentiated from focal
lesions [75 ]. Therefore, a well-demarcated
sonographically hypoechoic region within the pancreatic head without obstruction of
the MPD is a normal variant and has to be differentiated from abnormal focal
lesions. This finding is probably related to significant fat quantities in the
interlobular septa and acinar cells of the dorsal segment [72 ], and a change over time has been reported
[1 ]
[3 ].
Fig. 8 Pancreatic head transverse (a ) and longitudinal
(b ). Dorsally, the embryological ventral part is demarcated. This
is crescent-shaped, relatively smoothly bordered to the rest of the
pancreatic head, and less echogenic than the rest of the pancreatic head.
This is a physiological finding.
Factors influencing interpretation
An increase in echogenicity with age has been shown [3 ]
[17 ]
[32 ], whereas the influence
of BMI on echogenicity remains controversial (no correlation [32 ]; positive correlation [25 ]
[29 ]).
Pancreatic variations
There are various pancreatic appearances and shapes, some of which are considered
normal and others pathological.
Mobile pancreas
A mobile pancreas is a common phenomenon not often recognized in the daily
routine [Fig. 9 ]
[44 ]. Significant movement of the
pancreatic head in relation to the aorta and spine can be observed by changing
the patientʼs position from supine to left lateral. Knowledge of this phenomenon
is important for the correct interpretation of endoscopic ultrasound
examinations, often with the head and tail forming a “U” around the transducer.
Both parts of the organ can be seen on one image. The moving distance is
correlated to age and sex (especially in young healthy females) and is reduced
in the presence of chronic pancreatitis. No association has been reported
between the moving distance, body mass index (BMI), and splenic size [44 ].
Fig. 9 Mobile pancreas. In the left lateral position, the pancreas
shifts to the left. The pancreatic head is on the left lateral side of
the aorta.
Normal anatomical variants of the pancreas
Contour bulges
Nature of changes : Lobus-like contour protrusion on the pancreatic
head anteriorly, dorsally, or laterally. Description : Bulging of the
contour, same echogenicity as the rest of the parenchyma. Meaning :
Can be confused with pseudo-mass and tumors.
“Tuber omentale” [76 ]
Nature of changes : Contour bulge. Description :
Bulging/prominent anterior surface of the pancreatic body. Meaning :
Can be confused with enlargement of the pancreatic body and pseudo
masses.
Echogenicity
The nature of changes has been described above.
Congenital changes in the pancreas
Fusion anomaly
Nature of changes : Pancreas divisum [77 ]
[78 ]
[79 ]
[80 ]
[81 ].
Description : Failure of fusion of the pancreatic duct between the
ventral and dorsal bud of the pancreatic head during embryonic development.
The connection between the two parts of the duct is completely or
incompletely missing. The larger part of the pancreas - the dorsal bud
(dorsal part of the pancreatic head, pancreatic body, and pancreatic tail)
drains into the duodenum via the small minor papilla. The small part - the
ventral bud drains into the duodenum via the major papilla. Sonographically,
a pancreas divisum is suspected if the pancreatic duct is accentuated or
dilated in the dorsal bud of the pancreatic head, the pancreatic body, and
pancreatic tail and feeds into the duodenum at the level of the pancreatic
neck and the gastroduodenal artery. In contrast, the pancreatic duct is
small in the ventral bud of the pancreatic head.
Meaning : The ostium of the minor papilla may not be sufficient for the
pancreatic duct from the dorsal bud, and there may be congestion of the
pancreatic duct with recurrent episodes of pancreatitis and the development
of chronic pancreatitis. In this case, endoscopic interventions on the minor
papilla with pancreatic sphincterotomy are indicated. Diagnosis is usually
made by magnetic resonance cholangiopancreaticography (MRCP) or endoscopic
ultrasound.
Developmental (rotation and migration) anomalies
Nature of changes : Pancreas anulare [76 ]
[79 ]
[82 ]
[83 ]
[84 ]
[85 ]
[86 ]
[87 ]
[88 ]. Description : Incomplete
rotation of the ventral bud. The pancreas either completely or incompletely
surrounds the descending duodenum. Sonographic diagnosis is difficult. As a
rule, the diagnosis is made by MRI. By knowing the suspected diagnosis, the
diagnosis can also be made on radial EUS if care is taken to ensure that the
pancreas completely surrounds the duodenum. CT can also be used to diagnose
the annular pancreas, but an MRI examination that does not expose the
patient to radiation would be preferred. In the prenatal period and in
childhood, the “double bubble sign” has been described. This describes
dilatation of the stomach and duodenum due to duodenal stenosis. A
“crocodile jaw” configuration should raise suspicion of an incomplete
annular pancreas. A portal annular pancreas is an anomaly in which aberrant
pancreatic tissue completely surrounds the portal vein and/or venous
confluence. Meaning : An annular pancreas can lead to duodenal
stenosis. Other complications include post-bulbar ulcerations, pancreatitis,
and biliary obstruction. In childhood, pancreas anulare is often observed in
association with other congenital anomalies (esophageal atresia, imperforate
anus, heart defect, Down’s syndrome). If the diagnosis tends to remain
undetected until adulthood, these are more likely to be incidental findings
on imaging in the case of duodenal stenosis and gastric retention.
Branching anomaly
Nature of changes : Pancreas bifidum – tail fish pancreas [89 ]
[90 ]
[91 ]
[92 ]. Description : Branching
anomaly of the pancreas defined by its duplication in the pancreatic tail.
Meaning : Its clinical impact is not well established.
Parenchymal development anomalies
Nature of changes : Incomplete aplasia/hypoplasia/aplasia of parts of
the pancreas.
Description : Parts of the pancreas are missing. Meaning :
Exocrine and endocrine insufficiency may occur depending on the extent of
aplasia. The absence of parts of the pancreas on ultrasound may be
misinterpreted as poorly adjustable or “air-superimposed” pancreas.
A short introduction to pancreatic elastography
A short introduction to pancreatic elastography
Ultrasound elastography (USE) of the pancreas allows pancreatic tissue stiffness
assessment. A prerequisite of all kinds of elastography is the complete
visualization of the gland. Two main types of USE are used: Ultrasound strain
elastography (SE) and ultrasound shear wave elastography (SWE). Both techniques can
be applied endoscopically or transabdominally [93 ]
[94 ].
Comparatively little is known about the elastographic properties of the pancreatic
parenchyma [40 ]
[95 ]
[96 ].
Previous published studies on pancreatic stiffness are limited in number and are
heterogeneous in terms of study design, definition of health status, examination
technique (transabdominal versus endosonographic), ethical aspects (especially
invasive endosonographic examination of healthy subjects), examination technique
used (transient elastography, point shear wave elastography, 2D and 3D shear wave
elastography, strain imaging with histogram analysis, and all of the mentioned
techniques specifically and separately analyzed for the transabdominal versus the
endosonographic approach) [97 ]
[98 ]. A combined comparison of data and a
summary of reference values up to now is not possible [Fig. 10 ]. In addition, the different
characteristics of the pancreatic head, body, and tail, as well as the different
organ volumes, aging processes, and various confounding factors, must be considered.
We also refer to a separate publication on virtual touch imaging quantification
elastography in measurements of the pancreas [95 ].
Fig. 10 Endoscopic ultrasound images are shown with focal fatty
infiltration (between marker) and other degenerative signs (a ). Color
Doppler ultrasound reveals the supplying splenic vein branch (b ).
Different elastographic methods are shown in the same patient with a small
focal lesion (in between markers) being soft using strain imaging
(c ). Shear wave speed measurement with higher values (70 kPa) than
normal is shown in (d ) in comparison to a normal pancreas in
(e ) with 10.5 kPa.
A short introduction to contrast-enhanced ultrasound
A short introduction to contrast-enhanced ultrasound
Contrast-enhanced ultrasound (CEUS) can assess the vascularization of the pancreatic
parenchyma and focal lesions using the transabdominal and endosonographic approach.
CEUS is performed using the ultrasound contrast agents SonoVue® and
Sonazoid® with a device-specific low mechanical index of < 0.3. In the pancreas,
the arterial phase starts at 10–20 seconds and lasts until 35–40 seconds after
injection of the ultrasound contrast agent. Peak enhancement occurs at
22–26 seconds. In the parenchymal phase, enhancement decreases progressively [99 ]. Critical clinical applications are the
detection of pancreatic necrosis, the differentiation between the usually
hypoenhancing PDAC and the diverse group of iso- and hyperenhancing solid pancreatic
lesions, and the characterization of septa and mural nodules in pancreatic cystic
lesions [100 ]
[101 ].
Conclusion
In conclusion, complete assessment of the pancreas should be targeted in every
ultrasound examination of the abdomen, and it is possible in the vast majority of
cases if the examination technique is appropriate. The size of the pancreatic head
should be documented at least in two diameters. We recommend the documentation of
all three dimensions at least during the learning curve since “the pancreatic head
is larger than often assumed” [41 ], and the
pancreas is mobile during body position changes [44 ]. The diameter of the MPD should be documented in the pancreatic body
in all patients, as even a slight increase can be an important indication of early
PDAC [3 ]
[39 ]
[40 ]. Particular attention
should be directed to the aging processes of the parenchyma [1 ]
[3 ].
Due to lipomatous transformation, the echogenicity of the parenchyma increases with
the aging process and BMI, and this process often starts focally.
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