Solid pseudopapillary tumor of the pancreas: clinical features and imaging findings

Accepted Manuscript Solid pseudopapillary tumor of the pancreas: clinical features and imaging findings

Dong-Li Li, Hong-Sheng Li, Yi-Kai Xu, Quan-Shi Wang, RuiYing Chen, Fang Zhou PII: DOI: Reference:

S0899-7071(17)30200-0 doi:10.1016/j.clinimag.2017.10.006 JCT 8323

To appear in: Received date: Revised date: Accepted date:

23 December 2016 16 September 2017 9 October 2017

Please cite this article as: Dong-Li Li, Hong-Sheng Li, Yi-Kai Xu, Quan-Shi Wang, RuiYing Chen, Fang Zhou , Solid pseudopapillary tumor of the pancreas: clinical features and imaging findings. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Jct(2017), doi:10.1016/j.clinimag.2017.10.006

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Solid pseudopapillary tumor of the pancreas: clinical features and imaging findings

Dong-Li Li a, Hong-Sheng Li b, Yi-Kai Xu a,*, Quan-Shi Wang b, Rui-Ying Chen , and Fang Zhou a

PT

a

RI

a. Medical Imaging Center, Nanfang Hospital, Southern Medical University, Guangzhou

SC

510515, Guangdong, China.

b. PET Center, Nanfang Hospital, Southern Medical University, Guangzhou 510515,

NU

Guangdong, China.

MA

* Corresponding author: Prof. Yi-Kai Xu; Medical Imaging Center, Nanfang Hospital, Southern Medical University, No.1838 Guangzhoudadao Avenue north,

D

Guangzhou 510515, Guangdong, China.

PT E

Tel.: +862061642086; Fax: +862061642127; E-mail address: [email protected]

E-mail address:

CE

[email protected] (Dong-Li Li);

[email protected] (Hong-Sheng Li); [email protected] (Quan-Shi Wang);

[email protected] (Rui-Ying Chen);

[email protected] (Fang Zhou);

AC

[email protected] (Yi-Kai Xu);

Conflict of interest: None Funding: This study was supported by a grant from the National Natural Science Foundation of China (No. 81301215, and 81071174).

1

ACCEPTED MANUSCRIPT Solid pseudopapillary tumor of the pancreas: clinical features and imaging findings ABSTRACT This study aimed to report clinical features and CT, MRI, PET/CT findings of solid

PT

pseudopapillary tumor (SPT) of the pancreas. Thirty-four patients with pathologically proven SPT were retrospectively reviewed. Most patients were asymptomatic. SPTs in male patients

RI

mainly appeared as solid and near solid tumors. Mixed tumors and cystic tumors had larger size than solid and near solid tumors. Solid tumors and solid part of mixed tumors were T2

showed markedly even or uneven

18

SC

hyperintense and T1 hypointense and had progressive enhancement. Four tumors (80%) F-FDG uptake. These characteristic features can help

NU

differentiate SPT from other pancreatic neoplasms.

MA

Keywords:

Solid pseudopapillary tumor; Pancreas; Computed tomography; Magnetic resonance imaging;

AC

CE

PT E

D

2-Deoxy-2-[18F] fluoro-D-glucose; Positron emission tomography

2

ACCEPTED MANUSCRIPT 1. Introduction Solid pseudopapillary tumor (SPT) of the pancreas is a rare and probably misdiagnosed tumor with low malignant potential, accounting for 1-2% of all pancreatic tumors [1]. It was first described by Frantz in 1959 and also known as Frantz's tumor [2]. Pathogenesis,

PT

histogenesis and differentiation of SPT are still uncertain. Various names have been used to

RI

describe this lesion, such as solid and papillary tumor, solid-cystic tumor, papillary-cystic

SC

tumor, papillary epithelial neoplasm, papillary and solid neoplasm, solid and pseudopapillary epithelial neoplasm, and solid and cystic acinar cell neoplasm [3]. Grossly, SPT of the pancreas

NU

is a well encapsulated mass with variable degrees of internal hemorrhage and cystic

MA

degeneration. Microscopically, the tumor is composed of solid areas and variable cystic degeneration with characteristic pseudopapillae [4]. In 1996, the World Health Organization

D

(WHO) finally defined this neoplasm as "SPT of the pancreas ".

PT E

Although uncommon, the number of reported cases has increased over the past two decades due to the increased use of advanced imaging modalities and the accumulated

CE

awareness of this rare tumor. SPT predominantly occur in young female patients, especially in their second and third decade of life. It was reported that approximately 10-15% of cases of

AC

SPTs are malignant, but most SPTs are clinically indolent with a favorable prognosis following complete resection [5]. Accurate detection and characterization of SPTs of the pancreas and clear depicting of the relationships with adjacent structures are essential for ensuring appropriate operation and for preventing unnecessary resection. Diagnostic imaging such as computed tomography (CT), magnetic resonance imaging (MRI) and combined positron emission tomography and computed tomography (PET/CT) with

3

ACCEPTED MANUSCRIPT 2-deoxy-2-[18F] fluoro- D-glucose (18F-FDG) are of great value for preoperative diagnosis, operation plan and evaluation of prognosis of pancreatic tumors. However, clinical rarity and various non-specific presentations of SPTs of the pancreas made the preoperative diagnosis challenging.

18

F-FDG PET/CT findings were summarized, in order to help

RI

features, CT, MRI and

PT

In this study, thirty-four patients with SPT were retrospectively analyzed and their clinical

SC

radiologist familiar with them and achieve correct diagnosis. 2. Material and methods

NU

2.1. Patients

MA

A total of 34 patients (6 male and 28 female) with pathologically proven SPT of the pancreas from April 2010 to December 2015 were included in our retrospective study. The

D

mean age of the patients was 33.3 ± 13.1 years (range 10-62 years). Clinical features, imaging

PT E

findings, and pathologic confirmations of the diagnosis were recorded. All 34 patients had contrast-enhanced CT, five had 18F-FDG PET/CT and five had MRI available for review. All

CE

patients underwent surgical resection for primary tumor and SPT was pathologically confirmed

AC

by our pathologists. This retrospective study was approved by our institutional review board and the requirement for informed consent was waived. 2.2. Imaging procedures CT scans were performed using SOMATOM Definition scanner (Siemens Healthcare, Erlangen, Germany) or LightSpeed16 scanner (GE Medical Systems, Waukesha, WI, USA) before and after injection of contrast agent. Three-phase of enhanced CT scanning was performed. The scanning times for the arterial phase, portal venous phase, and delayed phase 4

ACCEPTED MANUSCRIPT were 20-25 s, 60-65 s, and 100-120 s, respectively. The scanning covered the area from the top of the diaphragm to beneath the liver with a 5-mm thickness of the reconstruction slice, 120 kV of tube voltage and automatic milliampere. Nonionic contrast agent was injected by high pressure syringe through elbow vein with 1.5 mL/kg of dosage and 2.5-3.0 mL/s of injection

PT

rate. The total amount of contrast agent was 60-90 mL.

RI

MRI examinations were performed using Signa Excite 3.0 T scanner (GE Medical

SC

Systems, Milwaukee, WI, USA). Imaging sequences include coronal and transverse T2- and T1-weighted fat suppressed images with 5- to 8- mm section thickness and a matrix size 160 ×

NU

256. Standard dynamic enhanced scanning was performed using a fat suppressed T1-weighted

MA

sequence before and after injection of contrast agent with 5 mm of slice thickness. The contrast agent gadopentetate dimeglumine was administrated at a dose of 0.1 mmol per kilogram of

D

body weight and an injection rate of 2.0 mL/s, followed by 20 ml of normal saline.

PT E

PET/CT examinations were performed using a Biography mCTX PET/CT scanner (Biography mCTX, Siemens, Germany). The imaging agent 18F-FDG (radiochemical purity >

CE

95%) was produced by PETtrace cyclotron (GE Medical Systems, USA). After fasting for more 18

F-FDG per

AC

than 6 h, patients were intravenously administered approximately 5.5 MBq of

kilogram of body weight when blood glucose concentration was less than 140 mg/dL. Whole body PET/CT imaging was started after resting in the dark room for 60 min and urination. A low dose CT scan for PET correction was first obtained, immediately followed by emission imaging covering 5-6 bed positions, with an acquisition time of 2.0 min per bed position. CT scan was performed using automatic electric current at a voltage of 140 kV, with a pitch of 0.75 and rotation time of 0.8 s. CT, PET and their fusion images were obtained by the iterative 5

ACCEPTED MANUSCRIPT reconstruction of CT X-ray data after attenuation correction. 2.3. Image analysis CT, MRI and

18

F-FDG PET/CT images were reviewed on a picture archiving and

communication system workstation monitor using the consensus of two radiologists with 10

PT

years’ experience. Imaging features were evaluated for the following characteristics: tumor

RI

size (longest diameter in centimeters), tumor shape, tumor location within the pancreas, tumor

SC

margins, density and solid-cystic ratio, presence of a capsule, calcifications, enhancement, bile or pancreatic duct dilatation, presence of parenchymal atrophy, lymphadenopathy, and

NU

presence and location of metastasis. CT values (Hounsfield units) of solid tumor, solid part of

MA

mixed tumor, the wall of cystic tumor, and normal pancreatic parenchyma in the body of the pancreas were measured on CT images before and each phase after injection of contrast agent.

D

Tumor to normal pancreas ratio (T/N) was calculated. The solid-cystic ratio was categorized

PT E

into five types (Table 1) according to proportion of each component, being “type I” if the lesion was purely solid, “type II” if the lesion was near solid with only small focal cystic degeneration

CE

on type I background, “type III” if the lesion present marked cystic degeneration but the solid

AC

portion was more than 50%, “type IV” if the solid portion was less than 50%, and “type V” if the lesion was purely cystic. The five types are also illustrated in Figs. 1, 2, 3, 4, and 5. The pancreatic localizations were classified as being at the head, neck, body, or tail. On MRI images, T1 and T2 signal intensity as well as enhancement was compared with adjacent pancreas parenchyma and categorized as “hypo”, “iso” or “hyper”. On 18F-FDG PET/CT images, 18F-FDG uptake was scored as increased or decreased than adjacent pancreas parenchymal activity. For semi-quantitative analysis, a region of interest was 6

ACCEPTED MANUSCRIPT drawn on each lesion in all axial sections, and maximum standard uptake value (SUVmax) was recorded. The SUVmax was defined as the ratio of activity per milliliter of tissue to the activity in the injected dose, corrected for the decay and for the patient’s body weight. 2.4. Statistical analysis

PT

Continuous variables are expressed as the mean ± standard deviation and categorical

RI

variables are expressed as number of patients or frequency (percent). Comparison of the patient

SC

ages between male and female patients was performed using Independent-samples t-test. CT values and T/N ratios in pre-contrast, arterial phase, portal venous phase and delayed phase

NU

were compared using one-way ANOVA. Chi-square test and one-way ANOVA were used to

MA

determine if there were differences in tumor characterization among five types of solid-cystic ratio of SPTs. Chi-square test and Independent-samples t-test were used to find factors that

D

correlated with malignant potential. The differences were considered significant when P-value

PT E

was less than 0.05. All statistical analysis were performed using the Statistical Package for Social Sciences version 13.0 for Windows (SPSS Inc., Chicago, Illinois, USA).

CE

3. Results

AC

3.1. Clinical features

From April 2010 to December 2015, a total of 34 patients (6 male and 28 female) with histopathologically proven SPTs of the pancreas were retrospectively analyzed. Their mean age was 33.3 ± 13.1 years (range 10-62 years). Among them, male patients aged from 25 to 59 years with the mean age of 38.7 ± 8.8 years, and female patients aged from 10 to 62 years with the mean age of 32.2 ± 13.7 years. The median ages of male and female patients were 39 and 31 years, respectively. There were four female patients over 50 years of age. There was no 7

ACCEPTED MANUSCRIPT statistical difference between the ages of male and female patients (38.7 ± 8.8 vs. 32.2 ± 13.7, t = 1.104, P = 0.278). Most patients (20/34, 58.8%) were asymptomatic and discovered incidentally during health examination or imaging studies following the workup for unrelated conditions. Vague

PT

abdominal discomfort and pain was the most frequent clinical symptom (10/34, 29.4%),

RI

followed by back pain after eating greasy food (2/34, 5.9%), abdominal pain accompany with

SC

repeated vomiting (1/34, 2.9%), and acratia and diarrhea (1/34, 2.9%).

Serum amylase levels and carcinoembryonic antigen (CEA) were all within normal ranges.

NU

Serum lipase and CA19-9 were elevated in three (3/34, 8.8%) and four (4/34, 11.8%) of patients,

MA

respectively. Serum α-fetoprotein (AFP) was elevated in one patient accompanied with hepatic carcinoma. Two patients had history of chronic pancreatitis.

D

The histological diagnosis was established with surgical resection in all patients.

PT E

Histopathologic features suggesting malignant potential were found in 12 patients (12/34, 35.3%), including pancreatic tissue infiltration (8/34, 23.5%), focal capsular invasion (3/34,

CE

8.8%), and hepatic metastases (1/34, 2.9%). All 34 tumors had no infiltration of surrounding

AC

organs or lymph node metastasis. Tumor recurrence was not found during the follow-up period (more than 6 months). Hemorrhage was identified in eighteen cases (18/34, 52.9%) on pathological findings. 3.2. CT findings All 34 patients had a single tumor representing SPT. Thirteen patients (13/34, 38.2%) were found to have tumor in the head of the pancreas, four patients (4/34, 11.8%) in the neck, seven patients (7/34, 20.6%) in the body, and ten (10/34, 29.4%) in the pancreatic tail. The average 8

ACCEPTED MANUSCRIPT tumor size was 5.4 ± 2.7 cm in the greatest diameter, ranged between 1.6 cm and 11.9 cm. There was no statistical difference between symptomatic and asymptomatic patients in tumor size (6.3 ± 2.5 vs. 4.9 ± 2.7, P = 0.138). Thirty-three tumors were round or oval in shape and one was lobulated. The tumor margin was well defined in twenty-six cases (26/34, 76.5%) and

PT

ill defined in eight cases (8/34, 23.5%). Twenty-six cases (26/34, 76.5%) presented exophytic

RI

lesion from the pancreatic gland, the center of the lesion located in the edge part of the pancreas

SC

or outside of the pancreatic contour, pushing around pancreatic tissue to form cup like impression.

NU

According to proportion of solid and cystic component observed on CT images, five types

MA

were categorized for SPT of the pancreas. Typical CT findings and uncommon findings of SPT were illustrated in Figs. 1 to 6. Demographic and CT findings were summarized in Table 2.

D

Type III, mainly solid tumor, was the most frequent (10/34, 29.4%), followed by type IV

PT E

(mainly cystic, 9/34, 26.5%), type I (solid, 7/34, 20.6%), type II (near solid, 4/34, 11.8%) and type V (cystic, 4/34, 11.8%). The tumor sizes of type I to type V of SPT were 2.5 ± 0.8 cm, 3.2

CE

± 0.8 cm, 6.2 ± 1.6 cm, 7.3 ± 3.1 cm and 6.7 ± 1.3 cm, respectively. Tumors of type III, type

AC

IV and type V had larger size than type I and type II (P < 0.05). There was no significant difference between the sizes of type I and type II tumors (P = 0.593). Type III, type IV and type V tumors also had no significant difference in tumor size (P > 0.05). The patient’ gender of the five types of SPT was different (P = 0.044). SPTs in male patients appeared as type I in three patients (3/6, 50%), type II in two patients (2/6, 33.3%), and type V in one patient (1/6, 16.7%). SPTs in female patients mainly appeared as type III (10/28, 35.7%) and type IV (9/28, 32.1%), followed by type I (4/28, 14.3%), type V (3/28, 10.7%) and type II (2/28, 7.1%). The presence 9

ACCEPTED MANUSCRIPT of capsule of the five types of SPT was also different (P = 0.003). Capsule was frequently (17/19, 89.5%) present in mixed solid -cystic tumors and cystic tumors (type III, IV and V). No significant difference was found among five types of SPT with respect to patient age, symptoms, tumor location, tumor margin, calcification, pancreatic or capsule invasion and

PT

enhancement pattern.

RI

All seven solid tumors of type I showed hypodense or slight hypodense to normal

SC

pancreatic parenchyma (Fig. 1). Tumors of type II were almost solid with only small focal cystic degeneration on type I background (Fig. 2). Mainly solid (type III) and mainly cystic

NU

(type IV) tumors showed mixed solid and cystic lesions, in which solid part showed hypodense

MA

or isodense while cystic part showed hypodense (Fig. 3, 4), except one tumor of type III showed hyperdense with CT value of 54 HU (Fig. 6 A). Mainly solid (type III) tumors manifested as

D

cystic areas scattered distributed within the solid part, especially in the periphery part of the

PT E

tumor (Fig. 3). There was no obvious boundary between cystic and solid areas. Mainly cystic tumors (type IV) manifested as solid part located in periphery of the lesion or as mural nodules

AC

cm (Fig. 5).

CE

(Fig. 4). Cystic tumors (type V) manifested as thick-walled cyst with wall thickness of 0.3-0.5

On enhanced CT images, solid tumors and solid part of mixed tumors had slight contrast enhancement in arterial phase, showed as hypodense to normal pancreatic parenchyma. In portal venous phase, solid tumors and solid part of mixed tumors had progressive enhancement and slightly increased or decreased enhancement in delayed phase, showed as slight hypodense or isodense to pancreatic parenchyma (Fig. 1-4). Cystic part of tumors had no obvious enhancement, but the wall enhanced similar to solid tumors (Fig. 5). 10

ACCEPTED MANUSCRIPT CT values and T/N ratios of the 34 tumors were measured and compared. CT values of the 34 tumors in arterial phase (54.29 ± 9.27 HU), portal venous phase (67.71 ± 9.46 HU), and delayed phase (65.65 ± 8.20 HU) were all higher than that in pre-contrast (35.85 ± 5.46 HU, all P < 0.001). CT values of the tumors in portal venous phase and delayed phase

PT

were both higher than in arterial phase (both P < 0.001). There was no statistical difference

RI

between CT values of the tumors in portal venous phase and delayed phase (67.71 ± 9.46

SC

HU vs. 65.65 ± 8.20 HU, P = 0.913). T/N ratio of the 34 tumors in arterial phase (0.52 ± 0.08) was significantly lower than in portal venous phase (0.78 ± 0.11), delayed phase (0.87

NU

± 0.11) and pre-contrast (0.80 ± 0.15, all P < 0.001). T/N ratio of the tumors in portal

MA

venous phase was lower than in delayed phase (P = 0.005). T/N ratios of the tumors in portal venous phase and in delayed phase had no statistical difference with that in pre-contrast (P =

D

0.998, P = 0.082, respectively). When divided into five types, there were no significant

PT E

differences among CT values of type I to V of the tumors in pre-contrast (P = 0.296) and in each phase of post-contrast CT imaging (P = 0.387, 0.203, 0.383, respectively, Table 2).

CE

Among the twelve cases with malignant potential, eight cases had pancreatic tissue

AC

infiltration, three cases had focal capsular invasion, and one had hepatic metastases. All these were found by postoperative pathologic analysis. Imaging examinations did not show satisfied results of these characteristics except for the hepatic metastases. The CT findings of hepatic metastases were consistent with those of primary tumor. We performed statistical analysis to find factors that correlated with the malignant potential. No significant difference was found between patients with and without malignant potential in patient age, gender, tumor size, and tumor location (P = 0.334, 0.293, 0.719, 0.369, respectively). 11

ACCEPTED MANUSCRIPT Hemorrhage manifested as scattered intratumoral hyperdense in three cases and slight hyperdense in five cases that can be identified by CT (Fig. 5, Fig. 6A, Fig. 8G), hemorrhage in other ten cases manifested as iso- or hypodense that cannot be distinguished from solid or cystic part of the tumor. The size of tumors with hemorrhage was significantly larger than that of

PT

tumors without hemorrhage (6.4 ± 2.8 vs. 4.4 ± 2.2, P = 0.033).

RI

Calcifications were seen in 12 lesions (12/34, 35.3%). Four patients had punctate

SC

calcifications and five had chunky, nodular calcifications in solid part of the tumor (Fig. 2A, Fig. 4B), and three patients had punctate or annular calcifications in peripheral solid part and

NU

capsule (Fig. 6B, C). Bile and pancreatic duct dilatation was found in three patients (Fig. 3).

MA

All of them had tumor located in the pancreatic head. Two patients had history of chronic pancreatitis and present pancreatic atrophy.

D

3.3. MRI findings

PT E

Demographic and MRI findings were summarized in Table 3. All five tumors on MRI were T2 hyperintense and T1 hypointense, and heterogeneous enhancement on contrast-

CE

enhanced T1-weighted images (Fig. 7). Cystic degeneration present as intratumoral T2

AC

hyperintense and T1 hypointense. Hemorrhage was found in two lesions as hyperintense within the mass on T1-weighted images (Fig. 8). Capsule was seen as a peripheral hypointense rim on T1- and T2-weighted images. After gadolinium administration, five tumors had progressive enhancement similar to that on CT images. Displacement of the surrounding vascular structures was found in two patients. Bile and pancreatic duct dilatation was not identified in any tumor. 3.4. PET/CT findings Demographic and PET/CT findings were summarized in Table 3. Five patients had 18F12

ACCEPTED MANUSCRIPT FDG PET/CT available for review. Three lesions were solid or near solid and two mixed solid and cystic. Their mean size was 4.7 ± 4.2 cm in the greatest diameter. Four tumors (4/5, 80%) showed markedly increased even or uneven (1/5, 20%) showed slightly increased

18

18

F-FDG metabolism (Fig. 7, 8) and one tumor

F-FDG metabolism. The average SUVmax of these

PT

tumors was 8.1 ± 5.9 (range 2.4-18.2). All five tumors had no infiltration of the surrounding

RI

organs or lymph node metastasis. No abnormal density or distribution of radioactivity was

SC

found in other parts of the body. 4. Discussion

NU

SPT of the pancreas is rare, but awareness of its importance in potential differential

MA

diagnosis has recently increased. SPT of the pancreas has the predilection to involve adolescent girls and young women, but has also been reported in older females, males and children [6, 7].

D

In the present study, there were 28 female and six male patients with SPT, and the female to

PT E

male ratio was nearly 5:1. There were four female patients over 50 years of age. There was no statistical difference between the ages of male and female patients in our study (38.7 ± 8.8 vs.

CE

32.2 ± 13.7, P = 0.278).

AC

Most SPTs of the pancreas grows slowly and have indolent behavior. Patients are usually asymptomatic and incidentally found in health examination or by abdominal imaging studies performed for other unrelated purposes. When the tumor grows large enough, it push organs around it and cause corresponding clinical symptoms [8]. But there was no statistical difference between symptomatic and asymptomatic patients in tumor size in our study (6.3 ± 2.5 vs. 4.9 ± 2.7, P = 0.138). This result indicates that the presence of symptoms has no correlation with tumor size. The reason may be that the tumor in this study is not large enough, or it may be 13

ACCEPTED MANUSCRIPT incompletely accurate because of the small sample size. An evaluation of a larger number of subjects seems to be necessary to confirm the results of this finding.

Main symptoms reported

in the literature include: vague abdominal discomfort and pain, nausea, poor appetite, vomiting, and dyspepsia, which are associated with tumor compression of the adjacent upper

PT

gastrointestinal system [9]. In this study, most of the patients (20/34, 58.8%) were

RI

asymptomatic and discovered incidentally during health examination or imaging studies

SC

following the workup for unrelated conditions, 29.4% (10/34) of the patients presented with vague abdominal discomfort and pain, 11.8% (4/34) of the patients presented with

NU

gastrointestinal symptoms, such as waist and back pain after eating greasy food, abdominal

consistent with the literature reports.

MA

pain accompany with repeated vomiting, diarrhea and fatigue. These clinical findings are

D

Usually, patients with SPT have normal serum amylase level and negative tumor markers

PT E

such as CEA, AFP, and CA19-9. Only two of the 116 patients (1.7%) reported by Yun-Qiang Cai et al. [6] had mildly increased CA19-9. In our study, Serum amylase levels and CEA were

CE

all within normal ranges. Serum lipase and CA19-9 were elevated in three (8.8%) and four

AC

(11.8%) of patients, respectively. Serum AFP was elevated in one patient accompanied with hepatic carcinoma. In the patients with increased CA19-9, two cases had pancreatic parenchyma encroached, and the other two cases had increased CA19-9 pre- and post resection of SPT. In three patients with increased pancreatic lipase, two cases had a history of chronic pancreatitis, considering the increase of the lipase may be associated with chronic pancreatitis. Therefore, hematology laboratory examination provides limited information for the diagnosis of SPT. Most of the patients with SPT, especially asymptomatic patients, were found 14

ACCEPTED MANUSCRIPT accidentally during the examination of abdominal imaging. SPT can occur in any part of the pancreas, and more commonly occurs in the head and tail of the pancreas [10]. In this group of cases, masses were separately located in the head, neck, body and the tail of the pancreas. In which, 38.2% (13/34) occurred in the head of the pancreas

PT

and 29.4% (10/34) occurred in the tail. Twenty-six cases (26/34, 76.5%) presented exophytic

RI

lesion from the pancreatic gland, the center of the lesion located in the edge part of the pancreas

SC

or outside of the pancreatic contour. The tumor may be quite exophytic, and occasionally their pancreatic origin may not be apparent, even at surgery. Infrequently it may occur at extra-

NU

pancreatic sites such as retroperitoneum, mesocolon or liver [11, 12].

MA

SPT of the pancreas has low-malignant potential and is curable with surgical complete excision in most instances. The overall 5-years survival is estimated to be more than 90%,

D

including patients with metastatic disease [13]. Therefore, correct preoperative diagnosis of the

PT E

tumor is crucial to minimize the range of surgical ablation compared to that required for pancreatic malignancy. Imaging examination plays an important role in the location of the

CE

tumor, evaluation of benign and malignant and the choice of surgical plan. CT and MRI are of

AC

great value for detection and characterization of SPT of the pancreas and clear demonstrating of the relationships with adjacent structures. Typically, SPT presents as a large encapsulated solid mass with clear border and varying internal cystic and hemorrhagic degeneration on CT [14]. Dynamic contrast enhanced CT shows slowly heterogeneous enhancement of solid components in portal venous phase and delayed phase. However, there are also some tumors that are almost entirely solid. In the study of Baek et al [15], SPTs with the diameter less than 3 cm frequently expressed as solid tumor 15

ACCEPTED MANUSCRIPT with clear boundary and gradually increased enhancement, weak during pancreatic phase and progressive during the hepatic venous phase. There were seven solid (7/34, 20.6%), four near solid (4/34, 11.8%) and twenty-three mixed or cystic (23/34, 67.6%) tumors in our study with the mean size of 5.4 ± 2.7 cm in

PT

maximum diameter. Capsule was found in 55.9% (19/34) of the tumors, mainly in mixed solid-

RI

cystic tumors and cystic tumors. The greatest diameters of solid and near solid tumors were all

SC

less than 5 cm. Mixed tumors (mainly solid, mainly cystic) and cystic tumors had larger size than solid and near solid tumors. Larger tumors tended to have a larger proportion of cystic

NU

component. SPTs in male patients mainly appeared as solid (50%) and near solid (33.3%)

MA

tumors. There was no significant association between solid-cystic ratio and patient age, symptoms, tumor location, tumor margin, calcification, pancreatic or capsule invasion and

D

enhancement pattern.

PT E

Solid tumors and solid part of mixed tumors were hypodense on unenhanced CT and had slight contrast enhancement on arterial phase, which remained hypodense to normal pancreatic

CE

parenchyma. In portal venous phase, solid tumors and solid part of mixed tumors had

AC

progressive enhancement, and slightly decreased or increased enhancement in delayed phase, showed as hypo- or isodense to pancreatic parenchyma. Cystic part of tumors had no obvious enhancement, but the wall enhanced similar to solid tumors. CT values of the tumors in portal venous phase and delayed phase were both higher than in arterial phase (both P < 0.001). There was no statistical difference between CT values of the tumors in portal venous and delayed phases (P = 0.913). T/N ratio of the tumors in portal venous phase was lower than in delayed phase (P = 0.005). These results confirmed the progressive enhancement feature of SPTs of the 16

ACCEPTED MANUSCRIPT pancreas. T/N ratio of the 34 tumors in arterial phase was significantly lower than that in portal venous phase, delayed phase and pre-contrast (all P < 0.001), which indicated that SPT can be clearly manifest in arterial phase with most obvious contrast to normal pancreas. Hemorrhage is one of the characteristics of SPT. Eighteen cases (18/34, 52.9%) with

PT

hemorrhage were confirmed by pathological examination in our study. Hemorrhage in eight

RI

cases manifested as hyperdense or slight hyperdense that can be identified by CT. Hemorrhage

SC

in the other ten cases manifested as iso- or hypodense that cannot be distinguished from solid or cystic part of the tumor. Hemorrhage may be manifest as hyper-, iso- or hypodense on CT

NU

images due to the amount and the time of bleeding. The size of tumors with hemorrhage was

MA

significantly larger than that of tumors without hemorrhage (6.4 ± 2.8 vs. 4.4 ± 2.2, P = 0.033). This result suggests that hemorrhage is more likely to occur in larger tumors. Hemorrhage can

D

be found in the cystic part but also solid part of the tumor. This has been postulated to be due

PT E

to the lack of powerful scaffold structure of the fragile and thin-walled vessels in the tumor [16]. Hemorrhage from microvessels within tumor tissues may frequently occur, as the

CE

weakened cell-to-cell adhesion might not fully support the microvasculature located within the

AC

solid tumor areas. Frequent hemorrhage, intratumoral necrosis, and dystrophic calcification are characteristic gross pathologic features of SPT [17]. Calcification is not infrequently seen in the internal or peripheral of the tumor. In this group of patients, hemorrhage and intratumoral necrosis were found in 79.4% (27/34) of the patients, and calcification were found in 35.3% (12/34) of the tumors, which was expressed as punctate, chunky, nodular or annular calcifications in the solid part of the tumor or capsule. It generally does not cause expansion of the bile duct and pancreatic duct, but when the 17

ACCEPTED MANUSCRIPT tumor in the head of the pancreas growth large enough, it may cause mild bile and pancreatic duct dilatation [18]. In this group, bile and pancreatic duct dilatation was found in three patients. All of them had tumor located in the pancreatic head. SPT tends to push and displace the surrounding structures rather than invasion.

PT

Although typically a non-aggressive neoplasm, metastasis or local invasion has been

RI

reported in approximately 10% to 15% of patients in the literature. The liver is the most

SC

common site for metastases [19]. Some studies have indicated that tumors occurring later in life seem to be more likely to behave aggressively, especially in male gender [14, 20]. Wang et

NU

al [21] found that when tumor size was > 6 cm, the probability of vascular involvement and

MA

capsular invasion increased significantly, and it also was more likely to present an aggressive behavior such as metastasis and recurrence. However, the youngest (10 years old) patient in

D

our series developed liver metastasis before operation. The CT findings of the hepatic

PT E

metastases were consistent with those of primary tumor. Although pancreatic tissue infiltration and focal capsular invasion were found in 32.4% (11/34) of the patients, none of them

CE

developed tumor recurrence on follow-up. Imaging examinations did not show satisfied results

AC

of pancreatic tissue infiltration and focal capsular invasion. No significant difference was found between patients with and without these malignant potential in patient age, gender, tumor size and tumor location (all P > 0.05). MRI is more accurate than CT in differentiating the cystic or solid component inside the tumor (Fig. 7) and can help distinguish SPTs from other pancreatic tumors. On T2 weighted images the cystic components are hyperintense, while the solid components have a heterogeneous intensity. MRI offers more specificity by directly demonstrating a hypointense 18

ACCEPTED MANUSCRIPT capsule on both T1 and T2 weighted images and hyperintense internal hemorrhage on T1 weighted images (Fig. 8). A fluid–fluid level hypointense on T2-weighted MRI has been described as representing a “hematocrit effect” [20]. Solid components with little or no hemorrhagic necrosis present hypointense on T1 weighted images and slight hyperintense on

PT

T2 weighted images. On gadolinium-enhanced dynamic MRI, the enhancement pattern is

RI

similar to that seen at CT, the most common consisting of peripheral and heterogeneous

lesion during portal venous and delayed phases [22].

SC

enhancement during the arterial phase with progressive but also heterogeneous fill-in of the

NU

There are only a few studies about the appearance of SPT on 18F-FDG PET or PET/CT in

MA

the literature. 18F-FDG PET/CT has been widely used for tumor detection and differentiation between benign and malignant lesions in staging work-up, therapeutic monitoring, and follow

D

up of various malignant conditions. However, previous reports suggested that it is difficult to

intense uptake of

18

PT E

differentiate benign and malignant SPT based on

18

F-FDG accumulation [23]. Moderate to

F-FDG were found even when there was no malignant expression. The

CE

reported SUVmaxs of primary SPTs were variable, from 2.6 to 16.2 [24]. The average SUVmax

AC

of the tumors in our study was 8.1 ± 5.9 (range 2.4-18.2) without malignant expression, which consistent with previous studies. The clinical significance of

18

F-FDG uptake, glucose

metabolism, and clinical usefulness of 18F-FDG PET/CT in SPT need to be further investigated. There are limitations to our study. First, because of the retrospective nature of our study, selection bias is inevitable. Second, only surgically confirmed SPT cases were enrolled, the ability to differentiate SPT from other pancreatic tumors was not evaluated. Another limitation is the small sample size, particularly the number of patients examined with MRI and 18F-FDG 19

ACCEPTED MANUSCRIPT PET/CT. Consequently, we did not compare the conspicuity or sensitivity of a certain finding on CT versus MRI and 18F-FDG PET/CT images. In conclusion, SPT of the pancreas is a rare low grade malignancy. It can occur in male and female patients, more predominantly in young women. Most patients were asymptomatic.

PT

SPTs in male patients mainly appeared as solid and near solid tumors. Larger tumors tended to

RI

have a larger proportion of cystic component. The typical imaging features include a well-

SC

circumscribed encapsulated lesion with variable degree of hemorrhage and cystic degeneration and progressed heterogeneous enhancement on dynamic CT and MRI. Small SPTs frequently

NU

present as purely solid lesions with sharp margins and gradual enhancement, weak during

MA

arterial phase and progressive during the portal venous phase. Markedly increased even or uneven 18F-FDG metabolism can be found in SPT without infiltration of surrounding organs

None.

CE

Funding

PT E

Conflict of interest

D

or lymph node metastasis.

AC

This study was supported by a grant from the National Natural Science Foundation of China (No. 81301215, and 81071174).

References [1] de la Santa LG, Retortillo JA, Miguel AC, Klein LM. Radiology of pancreatic neoplasms: An update. World J Gastrointest Oncol 2014; 6(9): 330-343. doi: 10.4251/wjgo.v6.i9.330 [2] Słowik-Moczydłowska Ż, Gogolewski M, Yaqoub S, Piotrowska A, Kamiński A. Solid pseudopapillary 2015; 9: 268. doi: 10.1186/s13256-015-0752-z 20

ACCEPTED MANUSCRIPT [3] Vilaça AF, Rodrigues P, Scigliano H, Pinto J, Reis A. Solid Pseudopapillary Tumor of the Pancreas: a rare and probably misdiagnosed neoplasm. J Radiol Case Rep 2011; 5(7):2434. doi: 10.3941/jrcr.v5i7.690 [4] Wood LD, Hruban RH. Pathology and molecular genetics of pancreatic neoplasms. Cancer J 2012; 18(6):492-501. doi: 10.1097/PPO.0b013e31827459b6

PT

[5] Wang XG, Ni QF, Fei JG, Zhong ZX, Yu PF. Clinicopathologic features and surgical outcome of solid pseudopapillary tumor of the pancreas: analysis of 17 cases. World J

RI

Surg Oncol 2013; 11:38. doi: 10.1186/1477-7819-11-38

[6] Cai YQ, Xie SM, Ran X, Wang X, Mai G, Liu XB. Solid pseudopapillary tumor of the

SC

pancreas in male patients: Report of 16 cases. World J Gastroenterol 2014; 20(22): 69396945. doi: 10.3748/wjg.v20.i22.6939

NU

[7] Park JY, Kim SG, Park J. Solid pseudopapillary tumor of the pancreas in children: 15-year experience at a single institution with assays using an immunohistochemical panel. Ann

MA

Surg Treat Res 2014; 86 (3): 130-135. doi: 10.4174/astr.2014.86.3.130 [8] Vargas-Serrano B, Dominguez-Ferreras E, Chinchón-Espino D. Four cases of solid

D

pseudopapillary tumors of pancreas: imaging findings and pathological correlations. Eur

PT E

J Radiol 2006; 58(1):132-139. doi: 10.1016/j.ejrad.2005.11.014 [9] Yu P; Cheng X; Du Y, Yang L, Xu Z, Yin W, Zhong Z, Wang X, Xu H, Hu C. Solid Pseudopapillary Neoplasms of the Pancreas: a 19-Year Multicenter Experience in China.

CE

J Gastrointest Surg 2015; 19(8):1433-1440. doi: 10.1007/s11605-015-2862-8 [10] Papavramidis T, Papavramidis S. Solid pseudopapillary tumors of the pancreas: review of

AC

718 patients reported in English literature. J Am Coll Surg 2005; 200(6):965-972. doi:10.1016/j.jamcollsurg.2005.02.011 [11] Zhu H, Xia D, Wang B, Meng H. Extrapancreatic solid pseudopapillary neoplasm: Report of a case of primary retroperitoneal origin and review of the literature. Oncol Lett 2013; 5(5):1501-1504. doi:10.3892/ol.2013.1242 [12] Tornóczky T, Kálmán E, Jáksó P, Méhes G, Pajor L, Kajtár GG, Battyány I, Davidovics S, Sohail M, Krausz T. Solid and papillary epithelial neoplasm arising in heterotopic pancreatic tissue of the mesocolon. J Clin Pathol 2001; 54(3): 241-245. doi:10.1136/jcp.54.3.241 21

ACCEPTED MANUSCRIPT [13] Kim MJ, Choi DW, Choi SH, Heo JS, Sung JY. Surgical treatment of solid pseudopapillary neoplasms of the pancreas and risk factors for malignancy. Br J Surg 2014; 101(10):12661271. doi: 10.1002/bjs.9577 [14] Choi JY, Kim MJ, Kim JH, Kim SH, Lim JS, Oh YT, Chung JJ, Yoo HS, Lee JT, Kim KW. Solid pseudopapillary tumor of the pancreas: typical and atypical manifestations. AJR Am

PT

J Roentgenol 2006; 187(2):W178-186. doi:10.2214/AJR.05.0569 [15] Baek JH, Lee JM, Kim SH, Kim SJ, Kim SH, Lee JY, Han JK, Choi BI. Small (
2010; 257 (1):97-106. doi: 10.1148/radiol.10092089

RI

solid pseudopapillary tumors of the pancreas at multiphasic multidetector CT. Radiology

SC

[16] Sperti C, Berselli M, Pasquali C, Pastorelli D, Pedrazzoli S. Aggressive behaviour of solidpseudopapillary tumor of the pancreas in adults: a case report and review of the literature.

NU

World J Gastroenterol 2008; 14(6):960-965. doi: 10.3748/WJG.14.960 [17] Sunkara S, Williams TR, Myers DT, Kryvenko ON. Solid pseudopapillary tumours of the

MA

pancreas: spectrum of imaging findings with histopathological correlation. Br J Radiol 2012; 85(1019):e1140-1144. doi: 10.1259/bjr/20695686

D

[18] Yin Q, Wang M, Wang C, Wu Z, Yuan F, Chen K, Tang Y, Zhao X, Miao F. Differentiation

PT E

between benign and malignant solid pseudopapillary tumor of the pancreas by MDCT. Eur J Radiol 2012;

81(11):3010-3018. doi: 10.1016/j.ejrad.2012.03.013

[19] Lestelle V, Coster C, Sarran A, Poizat F, Delpero JR, Raoul JL. Solid Pseudopapillary

CE

Tumor of the Pancreas: One Case with a Metastatic Evolution in a Caucasian Woman. Case Rep Oncol 2015;

8(3):405-408. doi: 10.1159/000441022

AC

[20] Cantisani V, Mortele KJ, Levy A, Glickman JN, Ricci P, Passariello R, Ros PR, Silverman SG. MR imaging features of solid pseudopapillary tumor of the pancreas in adult and pediatric

patients.

AJR

Am

J

Roentgenol

2003;

181(2):395-401.

doi:

10.2214/ajr.181.2.1810395 [21] Wang DB, Wang QB, Chai WM, Chen KM, Deng XX. Imaging features of solid pseudopapillary tumor of the pancreas on multi-detector row computed tomography. World J Gastroenterol 2009; 15(7): 829-835. doi: 10.3748/WJG.15.829 [22] Guerrache Y, Soyer P, Dohan A, Faraoun SA, Laurent V, Tasu JP, Aubé C, Cazejust J, Boudiaf M, Hoeffel C. Solid-pseudopapillary tumor of the pancreas: MR imaging 22

ACCEPTED MANUSCRIPT findings

in

21

patients.

Clin

Imaging

2014;

38(4):

475-482.

doi:

10.1016/j.clinimag.2014.01.015 [23]. Kang CM, Cho A, Kim H, Chung YE, Hwang HK, Choi SH, Lee WJ. Clinical correlations with (18) FDG PET scan patterns in solid pseudopapillary tumors of the pancreas: still a surgical enigma? Pancreatology 2014; 14 (6):515-523. doi: 10.1016/j.pan.2014.08.003

PT

[24] Kim YI, Kim SK, Paeng JC, Lee HY. Comparison of 18F-FDG PET/CT findings between pancreatic solidpseudopapillary tumor and pancreatic ductal adenocarcinoma. Eur J

AC

CE

PT E

D

MA

NU

SC

RI

Radiol 2014; 83 (1) 231-235. doi: 10.1016/j.ejrad.2013.09.031

23

ACCEPTED MANUSCRIPT

Table 1. Classification of SPT on CT images based on Solid-cystic ratio Type

Description

Solid-cystic ratio

type I

Solid

the lesion was purely solid

type II

Near solid

almost solid with only small focal cystic degeneration on type I background

type III

Mainly solid

present marked cystic degeneration but the solid portion was more than 50%

type IV

Mainly cystic

the solid portion was less than 50%

type V

Cystic

purely cystic

Total(N=34)

type

I

type

type

(n=7)

II(n=4)

III(n=10) 26.1±13.3

Age (years, mean±SD)

33.3±13.1

32.3±7.5

34.0±8.6

Tumor Size (cm, mean±

5.4±2.7

2.5±0.8

3.2±0.8

type

type

IV(n=9)

V(n=4)

RI

Parameter

PT

Table2. Demographic and imaging findings of SPT according to SPT CT types

40.0

±

p value

37.5±15.9

0.212

6.7±1.3

<0.001

SC

14.8

6.2±1.6

SD) Male

6

3

2

Female

28

4

2

Present

14

1

Absent

20

6

Location

MA

Symptoms

NU

Gender

7.3±3.1

0.044

0

0

1

10

9

3 0.393

1

6

3

2

3

4

6

2 0.071

13

1

0

6

4

2

Neck

4

2

1

0

1

0

Body

7

2

3

2

0

0

tail

10

2

0

2

4

2

Ill defined Capsule Absent Calcification Present

5

3

6

8

4

1

4

1

0

2

19

2

0

5

8

4

15

5

4

5

1

0

AC

Present

26

0.516

CE

Well defined

PT E

Tumor Margin

D

Head

8

0.003

0.887 12

2

2

3

3

2

22

5

2

7

6

2

Present

12

2

2

3

4

1

Absent

22

5

2

7

5

3

36.00 ±

37.75

3.79

4.86

55.86 ±

52.75

Absent Pancreatic or Capsule invasion

0.873

CT value (HU) Pre-contrast

35.85

±

5.46 Arterial phase

54.29

±

24

±

38.20

±

6.11 ±

58.00

33.33

±

4.98 ±

49.56

33.50

±

0.296

±

0.387

6.95 ±

54.50

ACCEPTED MANUSCRIPT 9.27 Portal venous phase

67.71

±

9.46 Delayed phase

65.65

12.04

66.43 ±

62.00

6.71

14.12

64.29 ±

60.25

4.86

10.91

9.89 ±

73.10

6.80 ±

4.10 ±

68.50

64.56

14.53 ±

8.55 ±

4.95

64.22

±

9.19

RI SC NU MA D PT E CE AC

25

69.25

±

0.203

±

0.383

16.50

PT

8.20

±

5.05

69.50 13.37

ACCEPTED MANUSCRIPT Table 3. Demographic, MRI and 18F-FDG PET/CT findings of SPT of the pancreas

No.

Gender

Age

Size

(year)

(cm)

SolidLocation

Margin

Capsule

cystic

Pancreatic Calcification

Hemorrhage

ratio

duct

1

Female

37

1.6

Head

2

Male

34

3.0

Neck

3

Female

46

11.8

Tail

4

Male

37

2.5

Body

5

Female

28

6.7

Tail

6

Female

24

5.4

Head

7

Male

41

1.9

Neck

Well defined Well defined Well defined Ill defined Well defined Ill

Absent

Absent

C A

defined

Solid

Near solid Mainly cystic

Absent

No

No

Present

No

No

Present

Yes

Absent

Solid

Present

Present

cystic

D E

PT

Absent

E C

defined Ill

Absent

dilatation

Absent

Mainly solid

Solid

Imaging

T1 signal

T2 signal

18F-FDG

studies

intensity

intensity

uptake

Hyper

Slightly

homogeneous

increased

Hyper

Markedly

heterogeneous

increased

Hyper

Markedly

heterogeneous

increased

MRI,

I R

MRI,

N A

C S U No

T P

PET/CT

PET/CT MRI,

PET/CT

Hypo

hypo

hypo

No

No

MRI

hypo

Present

Yes

No

MRI

hypo

Present

Yes

Yes

PET/CT

Absent

No

No

PET/CT

M

26

SUVmax

2.4

5.8

18.2

Hyper heterogeneous Hyper heterogeneous Markedly increased Markedly increased

7.6

6.7

ACCEPTED MANUSCRIPT

Fig. 1. Type I, solid SPT of the pancreas in a 37-year-old female. Unenhanced axial CT image (A) demonstrates a pure solid mass (arrow) in the pancreatic head with hypodense to pancreatic parenchyma. The mass shows poorly enhancing on the arterial phase (B) and progressed on portal venous (C) and delayed phases (D) of dynamic contrast enhanced CT images (arrows), and manifests slight hypodense to pancreatic parenchyma on delayed phase image (D).

SC

RI

PT

Fig. 2. Type II, near solid SPT of the pancreas in a 33-year-old female. Unenhanced axial CT image (A) reveals a near solid mass with focal cystic degeneration and small calcification in the pancreatic neck. Dynamic contrast enhanced CT images (B, C D, arrows) demonstrate the mass with heterogeneous progressive enhancement over time. The solid component of the lesion shows hypo- or isodense to pancreatic parenchyma on portal venous (C) and delayed phases (D) of enhanced CT images (arrows).

PT E

D

MA

NU

Fig. 3. Type III, mainly solid SPT of the pancreas in a 25-year-old female. Unenhanced (A) and enhanced (B, C, and D) axial CT images demonstrate a well-circumscribed mass with solid and cystic components. Cystic areas (B, arrows) scattered distribute within the solid part, especially in the periphery part of the tumor. There is no obvious boundary between cystic and solid areas. The solid component of the lesion shows progressive enhancement over time, but is still hypodense to pancreatic parenchyma (B, C, and D). The lesion is displacing but not invading adjacent structures. On portal venous phases, the dilated pancreatic duct is found (E, arrows). Histopathology slice with haematoxylin and eosin stain (F, ×100) of the tumor demonstrates pseudopapillary structures composed of tumour cells arranged around small central vessels.

AC

CE

Fig. 4. Type IV, mainly cystic SPT of the pancreas in four patients (A: a 22-year-old female, B: a 59-year-old female, C: a 25-year-old female, D: a 47-year-old female). Axial CT images of four patients after intravenous contrast administration show predominantly cystic, well-encapsulated lesions located in the head of the pancreas. These tumors manifest as solid part located in periphery of the lesion or as mural nodules (white arrows). Cystic parts of tumors have no obvious enhancement. Solid parts enhance progressively after contrast. Nodular calcification is noted in solid part of the tumor (B, black arrow).

Fig. 5. Type V, cystic SPT of the pancreas in a 20-year-old female. Unenhanced and enhanced CT images show a large thick-walled cystic mass (white arrows) arising from head of pancreas with areas of hyperdense representing hemorrhage (A, black arrow). No solid or multi-septated lesion is seen in the mass. The wall enhanced progressively on dynamic contrast enhanced CT images (B, C and D).

Fig. 6. Uncommon findings of SPT of the pancreas. A: Hyperdense SPT of the pancreas in a 15-year-old female. 27

ACCEPTED MANUSCRIPT

RI

PT

Unenhanced axial CT image shows a hyperdense mass in the pancreatic tail (arrow) with CT value of 54 HU. Hyperdense within the lesion corresponds to hemorrhage. B: Lobulated SPT of the pancreas in a 24-year-old female. Arterial phase of enhanced axial CT image shows a lobulated lesion (white arrow) in the pancreatic head with punctate calcification. C: SPT of the pancreas with eggshell calcification in a 31-year-old female. Unenhanced axial CT image shows a hypodense mass in the pancreatic tail with peripheral eggshell calcification. D: SPT of the pancreas in a 25-year-old male with hepatic carcinoma. Arterial phase of enhanced axial CT image shows a mild enhanced mass in the pancreatic tail (white arrow). A markedly enhanced hepatic carcinoma is found in the liver (black arrows). E: Hepatic metastatic SPT in a 10-year-old female. A hypodense mass in the liver (black arrow) was found to grow larger one year after operation of SPT. Histopathology with haematoxylin and eosin stain (F, ×200) of the mass confirms the hepatic metastatic SPT.

MA

NU

SC

Fig. 7. SPT of the pancreas (type II) in a 34-year-old male. Axial fat suppressed T2-weighted image (A), coronal T2weighted image (B) and fat suppressed T1-weighted image (C) show a T2 hyperintense and T1 hypointense near solid lesion located in the neck of the pancreas. On dynamic gadolinium enhanced fat suppressed T1-weighted image, the lesion enhances mildly on arterial phase (D), progressed on portal venous phase (E) and slightly decreased on delayed phase (F) images (arrows). Cystic degeneration as intratumoral T2 hyperintense and T1 hypointense can be seen (A, B, D, and E). Punctate calcifications can be found in the lesion on unenhanced CT image (G). Axial 18F-FDG PET image (H) and PET/CT image (I) show a hypermetabolic lesion with markedly increased 18F-FDG uptake in the neck of the pancreas.

AC

CE

PT E

D

Fig. 8. SPT of the pancreas (type IV) in a 46-year-old female. Axial fat suppressed T2-weighted image (A), coronal T2weighted image (B) and fat suppressed T1-weighted image (C) show a large encapsulated mainly cystic lesion located in the tail of the pancreas. A hypointense capsule on T2-weighted image (B, arrow) and irregular hyperintense hemorrhage on T1-weighted image (C, arrow) can be seen. The solid part of the lesion shows T2 hyperintense and T1 hypointense, and progressive enhancement on dynamic enhanced fat suppressed T1-weighted images (D, E, and F). Unenhanced axial CT image demonstrates a sharply margined hypodense mass in the pancreatic tail with slight hyperdense corresponds to hemorrhage (G, arrow). Axial 18F-FDG PET image (H) and PET/CT image (I) show a heterogeneous hypermetabolic lesion with markedly increased uneven 18F-FDG uptake in the tail of the pancreas.

28

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

NU

SC

RI

PT

Figure 1

29

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

NU

SC

RI

PT

Figure 2

30

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

NU

SC

RI

PT

Figure 3

31

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

NU

SC

RI

PT

Figure 4

32

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

NU

SC

RI

PT

Figure 5

33

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

NU

SC

RI

PT

Figure 6

34

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

NU

SC

RI

PT

Figure 7

35

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

NU

SC

RI

PT

Figure 8

36

ACCEPTED MANUSCRIPT Highlights: 1. SPT of the pancreas predominantly occurs in young women. Most patients were asymptomatic. 2. SPTs in male patients mainly appeared as solid and near solid tumors. 3. Larger tumors tended to have a larger proportion of cystic component. 4. SPTs showed gradual enhancement on dynamic CT and MRI imaging.

PT

5. Markedly increased 18F-FDG metabolism was found in SPT without infiltration of surrounding organs

AC

CE

PT E

D

MA

NU

SC

RI

or lymph node metastasis.

37