Solid-pseudopapillary neoplasm of the pancreas: spectrum of findings on multidetector CT
Satomi Kawamotoa, Jennifer Scudiereb, d, Ralph H. Hrubanb, d, Christopher L. Wolfgangc, d, John L. Cameronc, d, Elliot K. Fishmana
a The Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins Medical Institutions, 601 North Caroline Street, Baltimore, MD 21287, USA
b Department of Pathology, The Johns Hopkins Medical Institutions, 601 North Caroline Street, Baltimore, MD 21287, USA
c Department of Surgery, The Johns Hopkins Medical Institutions, 601 North Caroline Street, Baltimore, MD 21287, USA
d The Sol Goldman Pancreatic Cancer Research Center and The Johns Hopkins Medical Institutions, 601 North Caroline Street, Baltimore, MD 21287, USA
Received 1 October 2009. Accepted 10 November 2009. Available online 13 January 2011.
http://dx.doi.org/10.1016/j.clinimag.2009.11.007
Abstract
Solid-pseudopapillary neoplasms of the pancreas are uncommon and usually occur in young women. They are generally large, encapsulated masses with mixture of solid, cystic, and hemorrhagic components. Some cases have atypical features; for example, they can form a small predominantly solid mass and produce dilatation of the main pancreatic duct. In this article we discuss and illustrate the spectrum of the appearances of this distinctive neoplasm on multidetector CT.
1. Introduction
Solid-pseudopapillary neoplasms (SPNs) of the pancreas are rare tumors that predominantly occur in young women. They were first described by Frantz in 1959 as a “papillary tumor of the pancreas, benign or malignant” [1]. This neoplasm is also known by other names including solid and papillary epithelial neoplasm, solid and cystic tumor, papillary–cystic neoplasm of the pancreas, Frantz tumor, and Hamoudi tumor [2]. In 1996, The World Health Organization renamed this tumor as solid-pseudopapillary and this name is now uniformly accepted [3].
The reported incidence of SPN of the pancreas is 0.13–2.5% of all pancreatic neoplasms [4], [5] and [6]. Most cases are found in women (>90%), and these tumors usually occur in the second or third decades of life [5]. Most SPNs are isolated to the pancreas, although 10–15% of patients will develop metastatic disease. Surgical resection is usually curative [7], [8] and [9].
The objectives of this article are to discuss and illustrate the spectrum of the appearance of SPN of the pancreas on multiphasic multidetector CT (MDCT) and to discuss findings that help differentiate SPN of the pancreas from other pancreatic masses. We will also briefly discuss the pathological and clinical features of SPN of the pancreas.
2. Pathological features
Most SPNs of the pancreas are large, well-demarcated masses with areas of hemorrhagic degeneration on cross section. SPNs are fundamentally solid tumors with extensive degenerative changes rather than truly cyst-forming neoplasms. Microscopically, SPNs are composed of uniform poorly cohesive oval-shaped cells [10]. SPNs contain multiple delicate branching vessels. The neoplastic cells immediately adjacent to these vessels appear intact, while the cells furthest from the vessels degenerate and are replaced by blood, producing pseudopapillary fronds and cystic spaces [10], [11] and [12].
Most SPNs are surrounded by a well-developed capsule, but some tumors invade the capsule and the surrounding structures [13]. A small number of SPNs of the pancreas metastasize, most commonly to the liver [13].
SPN can be found in any portion of the pancreas. Although the predominating site for SPN was reported in the tail of the pancreas [11], in other series, the masses were located in the head, body, and tail at a ratio of approximately 4:2:4 [6] and [7]. A few cases of SPN have been found adjacent to but anatomically separate from the pancreas [4] including in the mesocolon, omentum, retroperitoneum, and liver.
The exact histogenesis is unknown, and numerous hypotheses have been suggested. These neoplasms are, however, unified by the presence of β-catenin gene mutations [10]. These mutations help explain the poorly cohesive nature of the neoplastic cells.
3. Clinical features
Clinically, patients with SPN of the pancreas usually have vague abdominal symptoms such as fullness or discomfort. Some patients experience pain, and others have a palpable abdominal mass [4] and [6]. Some patients are asymptomatic and are incidentally discovered with imaging studies performed for other reasons [11]. Typically, laboratory tests (serum amylase) and tumor markers (CA19-9, CEA, and α-fetoprotein) are normal [14].
The treatment of choice is surgical resection, and the long-term prognosis for patients with a SPN of the pancreas is excellent after surgical resection [5], although local recurrence and metastases may occur. Lam et al. [6] reviewed 452 reported cases of SPN of the pancreas in the English literature, and reported that 66 of 452 neoplasms (15%) metastasized or invaded adjacent structures [4]. Metastasis reportedly occurred 12 to 131 months after original diagnosis, and therefore, long-term follow-up of these patients is required [6].
4. CT techniques
CT examinations were performed on MDCT scanners including a Siemens Sensation 16 or 64 scanner (Siemens Medical Solutions, Malvern, PA, USA). Detector collimation settings of 16×0.75 mm or 64×0.6 mm were used. The data were reconstructed 0.75-mm slice thickness at 0.5-mm intervals for multiplanar reformation (MPR) and three-dimensional (3D) imaging. For diagnostic reading, 3-mm slice thickness and 3-mm reconstruction interval were used. The image data were reconstructed with soft tissue algorithm and reviewed on a workstation (Leonardo, Siemens Medical Solutions) using interactive MPR and 3D rendering techniques, including maximal intensity projection and volume rendering.
Our MDCT examination protocol typically included arterial phase imaging at 25 s and early portal venous phase imaging at 55–60 s after the injection of an intravenous contrast material. We injected 120 ml of iohexol (Omnipaque 350; GE Healthcare, Princeton, NJ) via a peripheral venous line at 3 to 4 ml/s. After fasting for at least 2 to 3 h, each patent ingested 750–1000 ml of water. Typically, we administer 500 ml of water 30 min prior to the study and an additional 250 ml of water immediately prior to the study.
5. Appearance of SPN of the pancreas on multiphasic MDCT
Typically, CT shows a well-encapsulated heterogeneous mass in the pancreas with both solid and cystic components [11], [12], [13] and [15]. These tumors are generally large (Fig. 1, Fig. 2, Fig. 3 and Fig. 4), and reported mean transverse diameter in radiological series was 8–11.5 cm (tumor size ranging from 2.5 to 17.0 cm) [11], [12], [15] and [16].
Fig. 1. A 27-year-old woman with SPN of the pancreas. (A) Arterial-phase and (B) venous-phase axial images show large exophytic mass arising from tail of pancreas with central cystic region (arrowheads). Peripheral solid portion shows mild contrast enhancement between these two phases. (C) Venous-phase anterior volume-rendered image shows bilobular shape exophytic mass (large arrows) containing central cystic region. Small internal calcification (small arrow) is also seen. Pathologically, it was 10.5 cm SPN of pancreas involving tail of pancreas.
Fig. 2. A 39-year-old woman with SPN of the pancreas. (A) Arterial-phase and (B) venous-phase axial images show large cystic mass with heterogeneous internal attenuation in the tail of pancreas. There is amorphous area of soft tissue attenuation (arrows) that shows no clear contrast enhancement between these two phases and small area of linear enhancement (arrowhead) at periphery on venous phase. (C) Venous-phase anterior volume-rendered image shows cystic mass with heterogeneous internal attenuation. Pathologically, it was 6.0 cm SPN of the pancreas involving the tail of pancreas.
Fig. 3. A 31-year-old woman with SPN of the pancreas. (A) Arterial-phase and (B) venous-phase axial images show large complex cystic mass with peripheral solid component in body of pancreas. There are enhancing septum-like structures (arrowheads) and peripheral solid component (arrow) within mass. Small internal calcifications are also seen. (C) Arterial-phase anterior volume-rendered image shows displacement of common hepatic artery (large arrow) and gastroduodenal artery (arrowhead) as well as left gastric artery (small arrows) by mass. (D) Venous-phase anterior volume-rendered image shows displacement of portal vein (arrows) due to mass. Peripheral and internal calcifications (arrowheads) are also seen. Pathologically, it was 11.0 cm SPN of the pancreas.
Fig. 4. A 19-year-old woman with SPN of the pancreas. (A) Arterial-phase and (B) venous-phase axial images show large mass (arrow) with central coarse calcification in head of pancreas. Mass is slightly heterogeneous in attenuation without significant contrast enhancement between these two phases. Superior mesenteric vein is compressed (arrowhead) by mass, but is patent. (C) Venous-phase anterior volume-rendered image shows large mass (arrow) with central calcification and splaying of the duodenal loop (arrowheads). Pathologically, it was 12.0 cm SPN of the pancreas (images of this patient were used in Ref. [7]).
SPNs most commonly have a mixed cystic and solid in appearance [12] and [15] (Fig. 1, Fig. 2 and Fig. 3). Less commonly they are mostly cystic (Fig. 4) or mostly solid [12] and [14] (Fig. 5 and Fig. 6). This entire spectrum from a completely solid to an almost completely cystic mass may be encountered on CT [11], [12] and [15] depending on the extent of degenerative changes [12]. Solid areas are usually located in the periphery of the tumor, and cystic areas are usually located centrally [11], [12] and [15] (Fig. 1, Fig. 2 and Fig. 3). CT numbers in cystic regions vary from fluid attenuation equal to that of water to soft tissue attenuation in areas rich in blood [11] and [12]. Fluid-debris levels corresponding to cystic hemorrhagic cavities have been reported on CT, MR imaging, and ultrasound [11]. On MR imaging, areas of high signal intensity on T1-weighted images correspond to areas of hemorrhagic necrosis or hemorrhagic debris [11] and [16]. However, the absence of high T1 signal within the lesion should not exclude the diagnosis of SPN [17].
Fig. 5. A 36-year-old woman with SPN of the pancreas. (A) Arterial-phase and (B) venous-phase axial images show 3.5-cm hypoattenuating mass (arrow) in tail of pancreas with minimal homogeneous contrast enhancement. (C) Arterial-phase anterior volume-rendered image shows hypodense mass in tail of pancreas (arrows). Pathologically, it was 3.5 cm SPN of the pancreas.
Fig. 6. A 27-year-old woman with SPN of the pancreas. (A) Noncontrast, (B) arterial-phase, and (C) delayed-phase axial images show 2.5 cm slightly hypoattenuating solid mass (arrow) in body of the pancreas with small central calcification. The mass is solid and shows homogeneous contrast enhancement without cystic component. Pathologically, it was 2.5 cm SPN of the pancreas.
SPNs of the pancreas are usually angiographically hypovascular, and conventional angiography reveals mild to moderate vascularity with avascular regions corresponding to areas of extensive hemorrhage and/or necrosis with splaying and displacement of nearby vessels [12]. Similar findings can also be seen on 3D CT angiography and MPR images (Fig. 3).
Calcifications are commonly seen in SPNs. In a study by Buetow et al., 16 of 56 patients (29%) had calcifications. There may be peripheral rim calcifications [11], [13], [15] and [16] (Fig. 3), which can be dense and extensive [13] and [16]. Central, stippled calcifications may also be seen [13] (Fig. 1, Fig. 2, Fig. 4 and Fig. 6).
Fig. 7. A 25-year-old man with SPN of the pancreas. (A) Venous-phase axial and (B) oblique coronal MPR images show 3-cm round, slightly heterogenous cystic mass (arrow) in head of pancreas. There is mild dilatation of main pancreatic duct (arrowhead) in body of the pancreas. Pathologically, it was 3.0 cm SPN of the pancreas with cystic degeneration.
Some SPNs of the pancreas may have atypical features on CT [13]. For example, dilatation of the main pancreatic duct can be associated with SPN, and this feature may simulate ductal adenocarcinoma of the pancreas or other tumors [13] (Fig. 7). Small SPNs of the pancreas are less sharply circumscribed and may appear as an unencapsulated, soft tissue density mass [13] (Fig. 6). Small SPNs of the pancreas with predominantly solid components may be difficult to detect on CT [14].
Metastases occur in a small number of cases. Liver metastases may have complex features similar to SPNs in the pancreas [13]. Invasion into the tumor capsule, adjacent normal pancreatic parenchyma, adjacent organs, or vascular structures, may also be seen on CT [13].
Rarely, SPN of the pancreas may present acutely with rupture of the capsule and resulting hemoperitoneum, and those patients may require urgent surgery. Mao et al. [18] reviewed 292 reported cases in the literature and found eight such cases. Rupture may be related to acute trauma [19], but five of these eight cases were without any identifiable acute cause [18]. In these cases, CT may reveal disruption of the tumor capsule, and intraperitoneal or retroperitoneal hemorrhage (Fig. 8). These tumors may simulate a perior intrapancreatic hematoma [19].
Fig. 8. A 13-year-old woman with SPN of the pancreas presented with blunt abdominal trauma and abdominal pain. (A and B) Excretory-phase axial images show hemoperitoneum around spleen and liver (arrowheads) and heterogeneous soft tissue density mass (arrows) in the left upper abdomen. Note irregular contour of the mass (arrows) suggesting rupture of capsule. The patient was treated conservatively. (C) Venous-phase axial CT performed 21 months later shows well-encapsulated large cystic mass with peripheral areas of contrast enhancement (arrows). Pathologically, it was 10 cm SPN of the pancreas with extensive hemorrhage and necrosis.
6. CT findings to help differentiate SPNs from other tumors
Differential diagnosis of SPN of the pancreas on CT includes mucinous cystic neoplasm, nonfunctioning islet cell tumor (well-differentiated endocrine neoplasm), serous (microcystic) adenoma, pancreatoblastoma in pediatric patients, calcified hemorrhagic pseudocyst, and gastrointestinal stromal tumors arising from the adjacent gastrointestinal tract when tumor is exophytic and closely related to the pancreas. When a well-encapsulated pancreatic mass with cystic and solid component is encountered in a young female patient, SPN should top the differential diagnosis. The attenuation of the cystic areas is often higher than the attenuation of water reflecting hemorrhage in SPN, whereas it tends to be closer to the attenuation of water in mucinous cystic neoplasms [12]. Fluid-debris levels may be seen in SPN of the pancreas, and is a direct sign of hemorrhagic cystic degeneration [11]; however, this finding may also be seen in mucinous cystic neoplasms [16]. Calcifications are often seen in SPNs, but they can also be seen in mucinous cystic neoplasms and serous cystadenomas. When the tumor appears solid with little or no hemorrhage or necrosis depicted by CT, it may be difficult to differentiate SPNs from other tumors, such as ductal adenocarcinoma, serous adenoma, and nonfunctional well-differentiated endocrine neoplasm, although the finding of normal caliber of the pancreatic duct supports the diagnosis of a SPN. Fine-needle aspiration biopsy may play a role in preoperative planning by helping distinguishing SPN from other pancreatic lesions [6] and [14].
7. Conclusions
SPN of the pancreas is an uncommon neoplasm that is usually found in young women. Typically, SPNs are large, well-encapsulated masses that demonstrate variable degrees of internal hemorrhage and cystic degeneration, and often associated with calcifications. When these features are encountered in a young female patient, this neoplasm should be a strong diagnostic consideration.
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