Solid Pseudopapillary Tumor of the Pancreas: Diagnosis with CT and MRI Mengsu Zeng, Xiuzhong Yao 曾蒙苏 姚秀忠 Department of Radiology, Zhongshan Hospital of Fudan University and Department of Medical Image, Shanghai Medical College of Fudan university, Shanghai, China

Background With the increasing radiological reports of Solid pseudopapillary tumor of the pancreas, its typical imaging features have been well known to radiologists. However, with the improvement in the imaging modalities and widespread use of CT and MRI, those atypical neoplasms have been becoming more and more common.

SOLID-PSEUDOPAPILLARY EPITHELIAL NEOPLASM 肿瘤实质和囊性成分 年轻女性 (35岁) 85% 边缘包膜清晰，境界规则 周缘或中心可见钙化（ 29% of 56 pts） -------Buetow, et al. Radiology 1996; 199:707 肿瘤位于胰腺体尾部较多见 手术切除预后好 （恶性程度与肿瘤大小、年龄正比） 李卉 曾蒙苏 等 中华放射学 2006，8：846 史讯 曾蒙苏 等 放射学实践 2007，11：356 史讯 曾蒙苏 等 中国医学计算机成像2007，13；370 姚秀忠 曾蒙苏等 中国肿瘤影像学杂志2010，5；458 中山医院 门诊大楼

The purpose of this study was to investigate the accuracy of CT and MRI for diagnosis of solid pseudopapillary tumor of the pancreas (SPTP).

Material and Methods 39 patients with SPTP proven by histopathology were divided into the correct diagnosis and misdiagnosis group based on the preoperative imaging and histopathologic results. All CT and MR imaging signs, including gender, age, tumor size, modalities (CT or MRI), location, shape, capsule, cystic degeneration, hemorrhage, calcification and enhancement type, were retrospectively evaluated with a correlation to their pathologic findings and statistically analyzed.

Results Among 39 imaging cases, 15 (38.5%) misdiagnosed (mean age 41.07 years old) 24(61.5%) diagnosed. (mean age 26.75 years old, p=0.000). Tumor size tended to be smaller in the elder group and had a negative linear correlation with the patient age (r=-0.408, p=0.025). cause of higher misdiagnosis: correctly diagnosis : the older patients (p=0.007), gender, small tumors (p=0.037), location, CT (p=0.049) shape, non-hemorrhage (p=0.000) capsule, cystic degeneration, calcification type of enhancement . Macroscopically, large SPTPs were more likely to appear the capsule (p=0.002), cystic degeneration (p=0.003) and hemorrhage (p=0.029) than small tumors.

Results N Mean (cm) P value size misdiagnosis 15 5.0000 0.289 24 Table 1 Comparison of tumor size and age between two groups N Mean (cm) P value size misdiagnosis 15 5.0000 0.289 Correct diagnosis 24 6.1167 age 41.0667 0.000 26.7500

Results Graph 1 Linear regression analysis of tumor size and patient age Note: Bconstant=7.435, p=0.000; Bage=-0.067, p=0.025

Table 2 imaging Analysis Evaluations correct diagnosis misdiagnosis Misdiagnosis Rate P value Gender Male 3 50.0% Female 21 12 36.4% 0.658 Age＊ The elder(≥40) 5 10 66.7% The younger(＜40) 19 22.8% 0.007 Size＊ Large (＞3.0cm) 22 9 29.0% Small (≤3.0cm) 2 6 75.0% 0.037 Modalities＊ CT 11 52.2% MRI 13 38.5% 0.049 Location Head 7 46.2% Body 40.0% Tail 8 2.3% 0.631 Shape Round 38.9% Oval 4 33.3% Lobulated 44.4% 0.873 Capsule Presence 20 28.6% Absence 63.6% 0.068 Cystic degeneration 17 32.0% 50% 0.318 hemorrhage＊ 1 8.3% 14 51.9% 0.013 calcification 35.5% 0.686 gradual enhancement 37.5% 1.000 Table 2 imaging Analysis of SPTP between Two groups

Results Table 3 Tumors’ demonstrations between CT and MRI Findings CT P value Capsule Presence 14 Absence 9 2 0.086 Cystic degeneration 12 13 11 3 0.093 hemorrhage 1 22 5 0.000 calcification 8 15 0.028 gradual enhancement 21 0.547

Table 4 Histopathological analysis in tumor size and patient age Results Table 4 Histopathological analysis in tumor size and patient age Findings Size Group P value Age Group Large Small The elder The younger Capsule Presence 23 1 7 17 Absence 3 5 0.002 0.116 Cystic degeneration 22 6 4 0.003 0.049 hemorrhage 18 14 8 0.029 0.150 calcification 2 1.000

Fig. 1.—23-year-old woman with a typical solid pseudopapillary tumor of pancreas Fig. 1a (a) Photograph of gross surgical specimen demonstrates the fibrous capsule, hemorrhagic areas and cystic degeneration.

Fig. 1b Fig. 1c Fig. 1.—23-year-old woman with a typical solid pseudopapillary tumor of pancreas (b, c) T2 weighted image and T1 weighted image with fat suppression showed the typical imaging features: the capsule, cystic degeneration and hemorrhagic areas.

Fig. 1e Fig. 1d (d, e,f) Dynamic contrast-enhanced MR scans revealed the early peripheral enhancement with progressively fill in and delayed enhancement of the capsule. Fig. 1f

Fig. 2.—19-year-old woman with a solid pseudopapillary tumor of pancreas misdiagnosed as mucinous cystic adenocarcinoma. Fig. 2a (a) Photograph of gross surgical specimen demonstrated the septations among chamberlets with cystic degeneration and the incomplete pseudocapsule.

Fig. 2b Fig. 2c (b, c,d) Dynamic contrast-enhanced CT scans demonstrated the pseudoseptate type enhancement and contrast medium was progressively filled in from the septation and margin to the centre of tumors. Fig. 2d

Fig. 3 —51-year-old man with a small solid pseudopapillary tumor of pancreas. Fig. 3a (a) Photograph of gross surgical specimen demonstrated a small solid tumor with the thick and irregular rim.

Fig. 3b Fig. 3c (b) Axial T1-weighted image reveals the tumor’s rim with hyperintense and the solid portions with homogeneous hypointense. (c, d) The small tumor appeared imperceptible in the contrast-enhanced T1-weighted and CT images on the delayed phase. Fig. 3d

Fig. 4—49-year-old woman with a solid pseudopapillary tumor of pancreas misdiagnosed as an inflammatory mass. Fig. 4a (a) Photograph of gross surgical specimen demonstrated a relatively large solid tumor without pseudocapsule and hemorrhagic areas.

(b) Axial unenhanced CT showed Fig. 4c Fig. 4b (b) Axial unenhanced CT showed the swelling pancreatic head with isodensity. (c, d), Dynamic contrast-enhanced CT scans displayed a large tumor with markedly early and delayed enhancement in the pancreatic head. Fig. 4d

Conclusion To avoid misdiagnosis, it should be very careful to evaluate some characteristic imaging signs in small tumors and those occurred to the aged. Compared to CT, MR was much superior to avoid misdiagnosis of SPTP.