DOI: 10.1148/rg.264065012
RadioGraphics 2006;26:1211-1238
From the Archives of the AFIP
Pancreatic Tumors in Children: Radiologic-Pathologic Correlation1
Ellen M. Chung, LTC, MC, USA,
Mark D. Travis, LCDR, MC, USN and
Richard M. Conran, COL, MC, USA
1 From the Department of Radiologic Pathology, Armed Forces Institute of Pathology, Alaska and Fern streets NW, Washington, DC 20306-6000 (E.M.C.); the National Capitol Radiology Consortium, National Naval Medical Center, Bethesda, Md, and Walter Reed Army Medical Center, Washington, DC (M.D.T.); the Institute for Pediatric Medical Education, Uniformed Services University of the Health Sciences, Bethesda, Md (R.M.C.); and the Department of Pathology, Georgetown University School of Medicine, Washington, DC (R.M.C.). Received February 2, 2006; revision requested March 13 and received April 21; accepted April 21. All authors have no financial relationships to disclose.
Address correspondence to E.M.C. (e-mail: chunge{at}afip.osd.mil).
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Abstract
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Pancreatic neoplasms are rare in children and have a different histologic spectrum and prognosis than those in adults.
In general, these tumors are well demarcated with expansile rather than infiltrating growth patterns. They may be quite large at diagnosis, and central cystic necrosis is common. They infrequently cause biliary duct obstruction. The imaging appearance of each neoplasm reflects its pathologic features.
Pancreatoblastoma is the most common pancreatic neoplasm in young children. At imaging, pancreatoblastomas are heterogeneous and often multilocular with hyperechoic and enhancing septa.
Solid-pseudopapillary tumor occurs in adolescent girls. It is heterogeneous in internal architecture, with a mixture of solid and cystic hemorrhagic and necrotic elements. This tumor is distinguished by its fibrous capsule and hemorrhagic nature, which are best shown at magnetic resonance imaging as a dark rim on T1- or T2-weighted images and hyper-intense foci on T1-weighted images, respectively. Islet cell tumors in children are insulinomas or gastrinomas. These tumors manifest early due to hormonal syndromes and are distinguished by their small size, homogeneous appearance, and intense enhancement with intravenous contrast material. All pancreatic neoplasms in children are capable of producing metastases, usually to the liver and lymph nodes; however, on the whole, these tumors have a better clinical outcome than most pancreatic tumors in adults. Knowledge of the differential diagnosis of pancreatic masses in children and their relatively good prognosis may promote correct preoperative diagnosis and appropriate treatment.
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LEARNING OBJECTIVES FOR TEST 6
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After reading this article and taking the test, the reader will be able to:- Describe the imaging features of pancreatic tumors in children and the pathologic bases of these features.
- Identify the features of each of these tumors that may allow differentiation from other pancreatic masses in children.
- Discuss the differential diagnosis and management of pancreatic masses in pediatric patients.
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Introduction
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Pancreatic tumors are quite rare in children, causing less than 0.2% of malignant pediatric deaths (1). The scarcity of cases limits our ability to study these tumors. Even authors from large referral centers, reporting their experience over 20–35 years, have encountered only small numbers of cases (2–5). In a surgical review of 92 pancreatic disorders in children over a period of 10 years, only 10 cases were tumors (6). In addition, confusing and evolving nomenclature makes it difficult to compare current cases to more remote cases in the literature. In general, pancreatic tumors in children have a different histologic spectrum and better clinical outcome compared to those in adults.
Pancreatic neoplasms are divided into epithelial and nonepithelial types (Table). Epithelial tumors may be further classified as exocrine or endocrine. Exocrine tumors may be of acinar, ductal, or undetermined cell origin. Only a small subset of the described neoplasms occurs in the pediatric population. The acinar cell tumor that occurs almost exclusively in children is pancreatoblastoma. Although rare, pancreatoblastoma is the most common pancreatic tumor of young children. Carcinoma of acinar cell origin has rarely been reported in older children. Ductal adenocarcinoma and its many variants are the most common pancreatic tumors in adults, but these are exceedingly rare in children. No convincing cases of the cystic neoplasms (serous cystadenoma and mucinous cystic neoplasm) have been reported in children (7). Solid-pseudopapillary neoplasm, currently classified as an epithelial neoplasm of uncertain cellular origin, is most commonly diagnosed in adolescent girls and young women. Endocrine cell tumors are uncommonly encountered in older children, and focal or diffuse neuroendocrine adenomatosis of the gland can cause neonatal hypoglycemia. Nonepithelial neoplasms arising primarily in the pancreas are quite rare in children. These include lymphoma, primitive neuroectodermal tumor, and mesenchymal tumors. Secondary involvement of the pancreas by adjacent tumor, especially neuroblastoma, may be difficult to distinguish from a primary pancreatic tumor and is much more common than the latter. Congenital and acquired cystic lesions can occur in children and mimic cystic neoplasms.
In this article, the clinical, pathologic, and imaging features and prognosis of the most common pancreatic neoplasms affecting children are reviewed, illustrated, and correlated. The differential diagnosis of pancreatic masses in children is discussed.
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Pancreatoblastoma
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Pancreatoblastoma, also called pancreaticoblastoma or infantile-type carcinoma of the pancreas, is the most common pancreatic tumor of young children (8). Like all pancreatic tumors in children, pancreatoblastoma is rare, accounting for only 0.2% of 645 pancreatic tumors reviewed by Cubilla and Fitzgerald (9). The tumor was first described in a 15-month-old boy as "infantile adenocarcinoma of the pancreas" by Becker (10) in 1957. In subsequent case reports, Horie et al (11) in 1977 observed histologic similarities to the normal embryonic appearance of the pancreas at 8 weeks gestation, analogous to other embryomas, and proposed the name pancreatoblastoma. Since then, fewer than 75 cases have been reported in the literature.
Clinical Features
Pancreatoblastoma most commonly occurs in the first decade of life. The age range is fetus to 9 years (mean, 4.5 years), although rare cases in adults have been reported (11–16). There is a male predominance ranging from 1.3:1 to 2.7:1 (8,14,17). More than half of reported cases are in Asians (8,17). Patients most commonly present with an asymptomatic, large abdominal mass (15,18–20). Those with symptoms usually have nonspecific complaints such as abdominal pain, fatigue, lethargy, weight loss, anorexia, diarrhea, or vomiting (13–15,18). Jaundice is uncommon (8,13,14). There are reports of associated elevated 
-fetoprotein level in up to one-third of patients (8), as seen in other embryonal tumors such as hepatoblastoma and embryonal carcinoma.
Congenital cases of pancreatoblastoma have been described in association with Beckwith-Wiedemann syndrome, and these are predominantly cystic in nature (16,21). Beckwith-Wiedemann syndrome is a genetic, systemic disorder characterized by macrosomia, macroglossia, omphalocele, and visceromegaly. Patients are at increased risk of developing embryonal tumors, including nephroblastoma, hepatoblastoma, rhabdomyosarcoma, and pancreatoblastoma (16,21,22). The risk of malignancy is estimated to be about 4% (23).
For information on the molecular genetics of pancreatoblastoma, see Appendix E1 at radiographics.rsnajnls.org/cgi/content/full/26/4/1211/DC1.
Pathologic Features
Gross Features.—
Pancreatoblastomas are usually large, solitary masses (Fig 1). The size range is 1.5–20 cm with a mean of 10.6 cm (14). Approximately half arise in the head of the pancreas (8,13,15). The tumor is a well-defined or partially circumscribed, solid mass with lobulated margins (Fig 1) (8,14,24). The cut surface is yellowish to tan with lobulations separated by fibrous bands (13–15). The mass may contain cystic spaces due to hemorrhagic necrosis and cystic degeneration (8,9,24) (Fig 1). They may be grossly cystic, as reported in most cases associated with Beckwith-Wiedemann syndrome (21).
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Figure 1a. Pancreatoblastoma in an 11-year-old girl who presented with abdominal pain, vomiting, and syncope after minor trauma. (a) Computed tomographic (CT) scan enhanced with intravenous contrast material shows a large, well-circumscribed, heterogeneous mass growing exophytically from the body and tail of the pancreas. Round, unenhancing cystic areas (arrow) and foci of intense enhancement (arrowheads) are noted within the mass. (b) Photograph of the cut surface of the resected gross specimen shows the encapsulated heterogeneous mass with cystic components filled with serous fluid (arrows). (c) Photomicrograph (original magnification, x16; hematoxylineosin [H-E] stain) shows small, rosette-like glandular structures (arrows) intermixed with solid sheets of uniform epithelial cells (arrowheads).
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Figure 1b. Pancreatoblastoma in an 11-year-old girl who presented with abdominal pain, vomiting, and syncope after minor trauma. (a) Computed tomographic (CT) scan enhanced with intravenous contrast material shows a large, well-circumscribed, heterogeneous mass growing exophytically from the body and tail of the pancreas. Round, unenhancing cystic areas (arrow) and foci of intense enhancement (arrowheads) are noted within the mass. (b) Photograph of the cut surface of the resected gross specimen shows the encapsulated heterogeneous mass with cystic components filled with serous fluid (arrows). (c) Photomicrograph (original magnification, x16; hematoxylineosin [H-E] stain) shows small, rosette-like glandular structures (arrows) intermixed with solid sheets of uniform epithelial cells (arrowheads).
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Figure 1c. Pancreatoblastoma in an 11-year-old girl who presented with abdominal pain, vomiting, and syncope after minor trauma. (a) Computed tomographic (CT) scan enhanced with intravenous contrast material shows a large, well-circumscribed, heterogeneous mass growing exophytically from the body and tail of the pancreas. Round, unenhancing cystic areas (arrow) and foci of intense enhancement (arrowheads) are noted within the mass. (b) Photograph of the cut surface of the resected gross specimen shows the encapsulated heterogeneous mass with cystic components filled with serous fluid (arrows). (c) Photomicrograph (original magnification, x16; hematoxylineosin [H-E] stain) shows small, rosette-like glandular structures (arrows) intermixed with solid sheets of uniform epithelial cells (arrowheads).
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Histologic Features.—
Pancreatoblastoma is composed of epithelial tissue in an organoid arrangement of acinar, trabecular, or solid formations separated by dense stromal bands (Fig 1) and distinctive squamoid corpuscles (8,9). The acinar areas are composed of columnar or cuboidal cells surrounding luminal spaces. Scattered throughout the solid and glandular areas are islands of cells referred to as squamoid corpuscles, which are one of the most characteristic features of pancreatoblastoma. The islands are composed of cells with basophilic or clear cytoplasm in formations varying from islands of polygonal cells to whorled nests of spindled cells. These may demonstrate central keratinization. The stroma may be scant to abundant.
Imaging Features
Although the pathologic features of pancreatoblastoma are well described in the literature, few series describe the radiologic features of pancreatoblastoma. Often the mass is so large at presentation as to make determination of the organ of origin quite difficult. In the series of Montemarano et al (15), in only half of the cases did the imaging appearance suggest the pancreas as the organ of origin. These large tumors typically compress surrounding structures without appearing to invade them, although local invasion may be evident at surgical resection (11,13,15,18). Dilatation of the biliary tree is uncommon, although half arise in the pancreatic head and most are quite large at presentation. This is likely due to the soft consistency of the tumor (15). Identification of local adenopathy at imaging is difficult (15). Encasement of large arteries has been reported (17,18).
At sonography, the majority of pancreatoblastomas appear as well-circumscribed heterogeneous masses with solid and cystic components (15,17). Cystic structures are hypoechoic with hyperechoic internal septa (15,18,19,25). Occasionally, a hypoechoic, solid mass is seen (25).
At CT, the mass is most commonly well or partially circumscribed, although an infiltrative margin is uncommonly encountered (13,15). The tumor is often smooth and may be multilobulated (25). Although lobulation is typically identified at gross pathologic inspection, it is an inconstant finding at CT (15). In the majority of cases, the mass is heterogeneous due to internal cystic areas, reflecting areas of necrosis seen at pathologic inspection (Fig 1). Frequently, the tumor appears multiloculated with enhancing septa (15,18,25). Small punctate, clustered, or curvilinear calcifications may be identified (15,25). Although there are few reports of cases with imaging before and after administration of intravenous contrast material, attenuation similar to that of enhancing vessels is common at CT (15) (Fig 1). Hepatic metastases are typically hypoattenuating at CT.
Few reports or series describing the magnetic resonance (MR) imaging appearance of pancreatoblastoma exist, and those available involve small numbers of cases. Typically, pancreatoblastomas are well marginated with low to intermediate signal intensity on T1-weighted images and heterogeneous high signal intensity on T2-weighted images (13,15,20). Low signal intensity on T1-weighted images corresponds to foci of necrosis (26). One reported case demonstrated intense enhancement on MR images obtained with intravenous contrast material (15). One report of MR imaging of hepatic metastases demonstrated signal intensity characteristics paralleling those of the pancreatic primary tumor (15).
Invasion of adjacent organs and distant metastases may occur with pancreatoblastoma. If locally advanced, the tumor is poorly marginated and invades the surrounding pancreas, as well as peripancreatic tissue and adjacent organs (5,9, 14). Biliary invasion has been reported (15). Vascular invasion is rare, although portal and mesenteric vein invasion has been reported. Metastases to the liver and abdominal lymph nodes are found in 35% at presentation (13–15,18). Less commonly, metastases are seen in the lung and brain (15,24). Rare cases of metastasis to the omentum, pelvic cul-de-sac, colon, spleen, kidney, and adrenal glands have been reported (14,15).
Differential Diagnosis
When the mass is large and not clearly arising from the pancreas, common tumors of adjacent organs occurring in young children must be considered. These include neuroblastoma, Wilms tumor, hepatoblastoma, and other primary liver tumors. Non-Hodgkin lymphoma occurs in children in this age group and may involve the pancreas, especially Burkitt lymphoma. Predominantly cystic pancreatoblastomas can appear radiologically similar to solid-pseudopapillary tumor, but the epidemiologic characteristics of these two tumors are dissimilar. Cystic pancreatoblastomas tend to occur in newborn patients with Beckwith-Wiedemann syndrome, more commonly boys (27), whereas solid-pseudopapillary tumor tends to arise in adolescent girls and young women. Acinar cell carcinoma is pathologically similar to pancreatoblastoma, so there is overlap in their radiologic appearances. The two can be distinguished based on the age of the patient. Pancreatoblastoma occurs in children less than 10 years of age, whereas acinar carcinoma is almost exclusively seen in older patients. Endocrine neoplasms are very rare in this age group and commonly manifest while quite small due to hormonally mediated clinical syndromes, whereas pancreatoblastomas are typically rather large at presentation.
Treatment and Prognosis
Pancreatoblastomas are best treated with complete surgical resection. The benefit of adjuvant chemotherapy has not been fully elucidated, but chemotherapy is commonly used empirically (5). The long-term prognosis is good in the absence of metastatic disease with complete surgical resection (2,5,8,13,14,21,24), but recurrence is common, so long-term follow-up is compulsory.
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Solid-Pseudopapillary Tumor
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Solid-pseudopapillary tumor is a unique tumor of low malignant potential most commonly affecting females of reproductive age. This unusual tumor of unclear cellular origin was first described by Frantz (28) in 1959 in a report of three cases. The tumor was further characterized in a case involving a 12-year-old girl by Hamoudi et al (29) in 1970 and then proposed as a distinct tumor entity in 1981 by Klöppel et al (30). In 1996, the World Health Organization recognized the designation "solid pseudopapillary tumor" as a distinct tumor of the exocrine pancreas (31). The nomenclature has evolved over time but remains confusing. This tumor has been variously known as solid and papillary tumor, solid-cystic tumor, papillary cystic tumor, papillary epithelial neoplasm, papillary and solid neoplasm, solid and pseudopapillary epithelial neoplasm, solid and cystic acinar cell neoplasm, and Frantz tumor.
In the past, solid-pseudopapillary tumors were commonly misdiagnosed as nonfunctioning islet cell tumors, adenocarcinomas, cystadenomas, or pseudocysts (9,28,32,33). Recently, solid-pseudopapillary tumor has been recognized with increasing frequency, as its pathologic features have become better characterized. As of 2004, more than 700 well-documented cases had been reported in the English literature (34).
Clinical Features
Solid-pseudopapillary tumor is most commonly diagnosed in adolescent girls and young women, and a predilection for blacks and East Asians has been suggested. The age range is 2–85 years with a mean age of 21.97 years (33–37). Published reviews of the literature that separate patients by age have found that 22%–52.6% of patients are children (32,33,37,38). Most children with solid-pseudopapillary tumor present to medical attention in the second decade of life. Female patients account for 83%–98.5% of the reported cases (33–42). Zhou et al (42) reported a similar finding in children. There is no known genetic or hormonal factor to explain the strong female predilection. Several studies have suggested a racial predilection for blacks (9,35,41) and East Asians. In fact, Zhou et al (42) have suggested that solid-pseudopapillary tumor may represent the most common pancreatic tumor of Asian children.
Presenting symptoms are usually subtle and commonly include abdominal discomfort or pain and a mass. Jaundice is rare, even in patients with lesions involving the head of the pancreas (4,32, 33,42,43). Occasionally, solid-pseudopapillary tumors are asymptomatic and are discovered at abdominal imaging, physical examination, or laparotomy performed for other reasons, including health screening, abdominal trauma, and pregnancy (32,44–46). Tumor rupture and hemoperitoneum related to abdominal trauma have been reported (33,36,37,47–49).
For information on the molecular genetics of solid-pseudopapillary tumor, see Appendix E1 at radiographics.rsnajnls.org/cgi/content/full/26/4/1211/DC1.
Pathologic Features
Gross Features.—
Solid-pseudopapillary tumor is a slow-growing tumor. It is commonly large and circumscribed or encapsulated, with marked degenerative and hemorrhagic change (Fig 2). The tumors are usually round to ovoid and solitary and occur throughout the pancreas (8,33,40,42,50), although some investigators have observed a predilection for the tail (35, 36,48). In the largest review of the literature, Papavramidis and Papavramidis (34) reported that 247 of 688 tumors (35.9%) arose in the pancreatic tail and 234 (34%) in the pancreatic head. The tumors may be quite exophytic, and occasionally their pancreatic origin may not be apparent, even at surgery (48).
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Figure 2a. Solid-pseudopapillary tumor in a 12-year-old girl with a 2-week history of mild abdominal pain, nausea, vomiting, and pruritus. Laboratory examination revealed elevated results of liver function tests in an obstructive pattern. (a) CT scan enhanced with intravenous and oral contrast material shows a well-demarcated, predominantly hypoattenuating mass in the head of the pancreas. The mass deflects the superior mesenteric vein medially (curved arrow) and the common bile duct laterally (straight arrow). Note the dilated intrahepatic ducts (arrowheads). (b) Coronal CT image shows upward displacement of the main portal vein (arrow) by the mass. (c) Transverse color Doppler sonogram of the upper abdomen shows the heterogeneous mass with prominent peripheral vessels. (d) Photograph of the cut surface of the en bloc resected specimen shows the mass surrounding but not invading the opened common bile duct (arrow). Arrowhead = gallbladder, * = duodenum. (e) Photomicrograph (original magnification, x 16; H-E stain) shows the characteristic pseudopapillary formations of solid-pseudopapillary tumor (*).
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Figure 2b. Solid-pseudopapillary tumor in a 12-year-old girl with a 2-week history of mild abdominal pain, nausea, vomiting, and pruritus. Laboratory examination revealed elevated results of liver function tests in an obstructive pattern. (a) CT scan enhanced with intravenous and oral contrast material shows a well-demarcated, predominantly hypoattenuating mass in the head of the pancreas. The mass deflects the superior mesenteric vein medially (curved arrow) and the common bile duct laterally (straight arrow). Note the dilated intrahepatic ducts (arrowheads). (b) Coronal CT image shows upward displacement of the main portal vein (arrow) by the mass. (c) Transverse color Doppler sonogram of the upper abdomen shows the heterogeneous mass with prominent peripheral vessels. (d) Photograph of the cut surface of the en bloc resected specimen shows the mass surrounding but not invading the opened common bile duct (arrow). Arrowhead = gallbladder, * = duodenum. (e) Photomicrograph (original magnification, x 16; H-E stain) shows the characteristic pseudopapillary formations of solid-pseudopapillary tumor (*).
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Figure 2c. Solid-pseudopapillary tumor in a 12-year-old girl with a 2-week history of mild abdominal pain, nausea, vomiting, and pruritus. Laboratory examination revealed elevated results of liver function tests in an obstructive pattern. (a) CT scan enhanced with intravenous and oral contrast material shows a well-demarcated, predominantly hypoattenuating mass in the head of the pancreas. The mass deflects the superior mesenteric vein medially (curved arrow) and the common bile duct laterally (straight arrow). Note the dilated intrahepatic ducts (arrowheads). (b) Coronal CT image shows upward displacement of the main portal vein (arrow) by the mass. (c) Transverse color Doppler sonogram of the upper abdomen shows the heterogeneous mass with prominent peripheral vessels. (d) Photograph of the cut surface of the en bloc resected specimen shows the mass surrounding but not invading the opened common bile duct (arrow). Arrowhead = gallbladder, * = duodenum. (e) Photomicrograph (original magnification, x 16; H-E stain) shows the characteristic pseudopapillary formations of solid-pseudopapillary tumor (*).
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Figure 2d. Solid-pseudopapillary tumor in a 12-year-old girl with a 2-week history of mild abdominal pain, nausea, vomiting, and pruritus. Laboratory examination revealed elevated results of liver function tests in an obstructive pattern. (a) CT scan enhanced with intravenous and oral contrast material shows a well-demarcated, predominantly hypoattenuating mass in the head of the pancreas. The mass deflects the superior mesenteric vein medially (curved arrow) and the common bile duct laterally (straight arrow). Note the dilated intrahepatic ducts (arrowheads). (b) Coronal CT image shows upward displacement of the main portal vein (arrow) by the mass. (c) Transverse color Doppler sonogram of the upper abdomen shows the heterogeneous mass with prominent peripheral vessels. (d) Photograph of the cut surface of the en bloc resected specimen shows the mass surrounding but not invading the opened common bile duct (arrow). Arrowhead = gallbladder, * = duodenum. (e) Photomicrograph (original magnification, x 16; H-E stain) shows the characteristic pseudopapillary formations of solid-pseudopapillary tumor (*).
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Figure 2e. Solid-pseudopapillary tumor in a 12-year-old girl with a 2-week history of mild abdominal pain, nausea, vomiting, and pruritus. Laboratory examination revealed elevated results of liver function tests in an obstructive pattern. (a) CT scan enhanced with intravenous and oral contrast material shows a well-demarcated, predominantly hypoattenuating mass in the head of the pancreas. The mass deflects the superior mesenteric vein medially (curved arrow) and the common bile duct laterally (straight arrow). Note the dilated intrahepatic ducts (arrowheads). (b) Coronal CT image shows upward displacement of the main portal vein (arrow) by the mass. (c) Transverse color Doppler sonogram of the upper abdomen shows the heterogeneous mass with prominent peripheral vessels. (d) Photograph of the cut surface of the en bloc resected specimen shows the mass surrounding but not invading the opened common bile duct (arrow). Arrowhead = gallbladder, * = duodenum. (e) Photomicrograph (original magnification, x 16; H-E stain) shows the characteristic pseudopapillary formations of solid-pseudopapillary tumor (*).
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Solid-pseudopapillary tumors range in size from 0.5 to 34.5 cm with a mean of 6.08–10.5 cm (34,36). The mass is always well demarcated, and the larger tumors are surrounded by fibrous capsules (35,38,40,44,45,48,51,52) (Fig 3). The mass is usually soft, fleshy, and friable. Solid areas are mixed with central cystic areas filled with bloody fluid or debris (8,33,44) (Fig 3). The tumors vary from solid to nearly completely cystic, with the majority composed of a mixture of the two components. Nearly all tumors have some component of cystic hemorrhagic or necrotic change regardless of size (27,35,47,50,51); however, smaller tumors tend to be predominantly solid and larger tumors tend to be more cystic (26,48). Occasionally calcifications are seen, most commonly in the capsule (32,33,35,38,41,45).
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Figure 3a. Solid-pseudopapillary tumor in a 14-year-old girl who developed abdominal pain after sledding. (a) CT scan enhanced with intravenous contrast material shows a well-defined, fairly homogeneous, cystic mass arising in the tail of the pancreas (arrow). The mass enhances less than the adjacent normal pancreatic tissue. Arrowhead = splenic vein. (b) Axial T2-weighted MR image shows that the mass has heterogeneous internal signal intensity (arrow), which indicates that the mass is more complex than suggested by the CT findings. (c) Axial T1-weighted out-of-phase MR image shows that the mass has peripheral high signal intensity (arrow), a finding consistent with hemorrhage. (d) Axial gadolinium-enhanced MR image shows enhancement of only the capsule of the mass (arrow). (e) Photograph of the cut surface of the resected gross specimen shows the thick capsule (arrow) and predominantly gelatinous-appearing contents.
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Figure 3b. Solid-pseudopapillary tumor in a 14-year-old girl who developed abdominal pain after sledding. (a) CT scan enhanced with intravenous contrast material shows a well-defined, fairly homogeneous, cystic mass arising in the tail of the pancreas (arrow). The mass enhances less than the adjacent normal pancreatic tissue. Arrowhead = splenic vein. (b) Axial T2-weighted MR image shows that the mass has heterogeneous internal signal intensity (arrow), which indicates that the mass is more complex than suggested by the CT findings. (c) Axial T1-weighted out-of-phase MR image shows that the mass has peripheral high signal intensity (arrow), a finding consistent with hemorrhage. (d) Axial gadolinium-enhanced MR image shows enhancement of only the capsule of the mass (arrow). (e) Photograph of the cut surface of the resected gross specimen shows the thick capsule (arrow) and predominantly gelatinous-appearing contents.
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Figure 3c. Solid-pseudopapillary tumor in a 14-year-old girl who developed abdominal pain after sledding. (a) CT scan enhanced with intravenous contrast material shows a well-defined, fairly homogeneous, cystic mass arising in the tail of the pancreas (arrow). The mass enhances less than the adjacent normal pancreatic tissue. Arrowhead = splenic vein. (b) Axial T2-weighted MR image shows that the mass has heterogeneous internal signal intensity (arrow), which indicates that the mass is more complex than suggested by the CT findings. (c) Axial T1-weighted out-of-phase MR image shows that the mass has peripheral high signal intensity (arrow), a finding consistent with hemorrhage. (d) Axial gadolinium-enhanced MR image shows enhancement of only the capsule of the mass (arrow). (e) Photograph of the cut surface of the resected gross specimen shows the thick capsule (arrow) and predominantly gelatinous-appearing contents.
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Figure 3d. Solid-pseudopapillary tumor in a 14-year-old girl who developed abdominal pain after sledding. (a) CT scan enhanced with intravenous contrast material shows a well-defined, fairly homogeneous, cystic mass arising in the tail of the pancreas (arrow). The mass enhances less than the adjacent normal pancreatic tissue. Arrowhead = splenic vein. (b) Axial T2-weighted MR image shows that the mass has heterogeneous internal signal intensity (arrow), which indicates that the mass is more complex than suggested by the CT findings. (c) Axial T1-weighted out-of-phase MR image shows that the mass has peripheral high signal intensity (arrow), a finding consistent with hemorrhage. (d) Axial gadolinium-enhanced MR image shows enhancement of only the capsule of the mass (arrow). (e) Photograph of the cut surface of the resected gross specimen shows the thick capsule (arrow) and predominantly gelatinous-appearing contents.
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Figure 3e. Solid-pseudopapillary tumor in a 14-year-old girl who developed abdominal pain after sledding. (a) CT scan enhanced with intravenous contrast material shows a well-defined, fairly homogeneous, cystic mass arising in the tail of the pancreas (arrow). The mass enhances less than the adjacent normal pancreatic tissue. Arrowhead = splenic vein. (b) Axial T2-weighted MR image shows that the mass has heterogeneous internal signal intensity (arrow), which indicates that the mass is more complex than suggested by the CT findings. (c) Axial T1-weighted out-of-phase MR image shows that the mass has peripheral high signal intensity (arrow), a finding consistent with hemorrhage. (d) Axial gadolinium-enhanced MR image shows enhancement of only the capsule of the mass (arrow). (e) Photograph of the cut surface of the resected gross specimen shows the thick capsule (arrow) and predominantly gelatinous-appearing contents.
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Histologic Features.—
The histologic appearance of solid-pseudopapillary tumor is characterized by regions of solid, pseudopapillary, and cystic changes merging with one another. The tumor is primarily solid with a rich supply of small, poorly supported blood vessels. The solid components of the tumor are composed of sheets and nests of uniform, polygonal epithelioid cells arranged around a network of numerous small, delicate blood vessels, surrounded by varying amounts of collagen. The fragility of this vascular supply leads to secondary degenerative changes with formation of cystic areas of hemorrhagic and necrotic change. The remaining cells surround delicate hyalinized fibrovascular stalks containing the small blood vessels, forming pseudopapillae (Fig 2).
Imaging Features
The imaging features of solid-pseudopapillary tumor reflect the pathologic findings of cystic and solid components, intratumoral hemorrhage, a fibrous capsule, and, less commonly, calcification. When present, the fibrous capsule and internal hemorrhage are the features that distinguish solid-pseudopapillary tumor from other pancreatic tumors.
Occasionally, solid-pseudopapillary tumors are discovered incidentally on abdominal radiographs due to rim-like calcifications within the tumor capsule or chunky calcifications inside the tumor (35,47,53).
At ultrasonography (US) and CT, the tumor is usually large, well circumscribed, and quite variable in appearance depending on its composition. The mass almost always appears well demarcated, even in cases with pathologic findings of adjacent organ invasion (35,47) (Figs 2, 3). The fibrous capsule may be visualized as an echogenic or, less commonly, hypoechoic rim at US (50). The capsule is typically hypoattenuating at CT (51). The tumors are usually large at presentation and often compress adjacent structures rather than invading them (26,51) (Fig 2). Associated duct dilatation is uncommon even with large masses in the head of the pancreas (47,49). Solid-pseudopapillary tumors are frequently exophytic, and the origin from the pancreas may not be apparent.
The internal architecture varies from a solid mass to a thick-walled cyst, with most tumors appearing as a mixture of solid and cystic elements (49,54). Very small tumors may be completely solid and are usually homogeneous. Larger tumors tend to be centrally cystic with enhanced through transmission. Occasionally, the tumors are nearly completely cystic with a small amount of residual solid tumor at the periphery. Most commonly, solid-pseudopapillary tumors appear complex in internal architecture, with echogenic, solid components and variable amounts of hypo-echoic, cystic areas corresponding to hemorrhagic necrosis (50,51,55). They usually display no through transmission (56). Occasionally, the mass can be echogenic with enhanced through transmission corresponding to friable tumor with massive hemorrhagic necrosis (50). At CT, the solid portions of the mass are isoattenuating to the pancreas. The attenuation of the cystic components is slightly higher than that of fluid in the gallbladder, with attenuation coefficients of 20–50 HU, likely due to the presence of blood products and debris (41,47,49,54,56). Fluid-debris levels are seen in up to 20% of tumors (35). Less than one-third demonstrate internal septations (47,50). Calcifications were previously thought uncommon but may be seen in up to one-third of cases, usually in the periphery of the tumor (35,47,50,55).
Enhancement with intravenous contrast material increases the conspicuity of the tumor but is usually slight (47,56). Enhancement is limited to the solid portions of the tumor, most often at the periphery, with unenhancing fluid and debris centrally (35,47,54). A peripheral rim of enhancement can also be seen with a thick fibrous capsule (41,51) (Fig 3).
At MR imaging, a surrounding hypointense fibrous capsule and internal hemorrhage, seen as high signal intensity on T1-weighted images, are distinguishing features of solid-pseudopapillary tumor (26,35,49,54). Ohtomo et al (49) reported that four of five tumors studied had fibrous capsules and also exhibited dark rims around the tumors on T1-weighted images (51). Similar dark rims on T2-weighted images were described in all nine cases with MR imaging reported by Buetow et al (35) (Fig 3). The solid portions of the tumor are iso- to hypointense to pancreas on T1-weighted images and slightly hyperintense to pancreas on T2-weighted images (40,49,51). The presence of hemorrhage is a distinctive feature, which is present, at least focally, in most tumors and best shown on MR images (35,49,51,54) (Fig 3). On T1-weighted images, most tumors have foci that are hyperintense to normal gland and correspond to areas of hemorrhagic necrosis or debris. The signal intensity of these foci on T2-weighted images is variable, due to the presence of multiple degradation products of hemoglobin (35,49,54). The appearance of hyperintense foci on T1-weighted images was noted in six of six cases reported by Ohtomo et al (49), 22 of 22 cases reported by Sun et al (54), and 14 of 19 cases reported by Cantisani et al (40).
Few reports describe the appearance of solid-pseudopapillary tumor on gadolinium-enhanced MR images, but the enhancement pattern is similar to that seen at CT. Cantisani et al (40) describe early peripheral, heterogeneous enhancement or ring enhancement greater than that of the adjacent pancreas (Fig 3). They also observed progressive fill-in on dynamic enhanced images. On delayed postgadolinium images, almost all enhanced less than the adjacent normal pancreas overall. In seven of 10 cases, capsular enhancement was early and more intense than that of the rest of the tumor (40). Peripheral enhancement was seen in two of three cases reported by Buetow et al (35) and in nine of 11 cases reported by Sun et al (54).
At angiography, solid-pseudopapillary tumor is typically avascular to hypovascular and displaces vessels. Some blush is seen in the solid portions, usually at the periphery (41,47,51). This appearance distinguishes solid-pseudopapillary tumor from the hypervascular islet cell tumor.
Differential Diagnosis
The imaging appearance of solid-pseudopapillary tumor can overlap with that of other tumors and benign disease, such as pseudocyst, but its characteristic clinical presentation and encapsulated and hemorrhagic nature help distinguish solid-pseudopapillary tumor from other pancreatic lesions.
Treatment and Prognosis
Solid-pseudopapillary tumor is a slow-growing tumor usually with a benign clinical course but with the potential for aggressive behavior, so that it is treated with complete surgical resection.
About 85% of tumors are limited to the pancreas, and these patients have an excellent prognosis (36,37,48). More than 95% of patients with local disease are cured by complete resection (8,36, 44,48). In the past, some children were treated with limited or incomplete surgical resection due to misdiagnosis of an adenocarcinoma, the complete fibrous capsule making enucleation technically feasible, or reluctance to subject a child to a radical surgery. Unfortunately, some of these children went on to develop tumor recurrence and/or metastases, and a few eventually succumbed to the disease (34,42). Consequently, most authors recommend an attempt at curative resection for all patients with solid-pseudopapillary tumor (3,32,33,48).
Metastatic disease was initially thought to be rare, but, as the frequency of diagnosis of solid-pseudopapillary tumor increases, so do reports of aggressive behavior. Metastases develop in 7%–16% of patients, usually older women. Reports of metastases in children are rare (33,37,38,42,46). Liver metastases are usually solitary and may be amenable to surgical resection (48). Even if complete surgical resection of metastases or the primary tumor is not possible, patients with solid-pseudopapillary tumor still benefit from surgical debulking (8,32–34,36–38,44).
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Islet Cell Tumors
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Islet cell or neuroendocrine tumors are endocrine cell–derived tumors of the pancreas. Those that are benign are termed adenomas, while those that metastasize are called carcinomas. These tumors are most commonly discovered in middle age but may be encountered in older children. The age range is 7–83 years (8). The mean age at diagnosis of insulinoma is 47 years for all patients and 25 years for patients with multiple endocrine neoplasia type 1 (MEN 1) (57). Of symptomatic insulinomas diagnosed during a 60-year period at the Mayo Clinic, 4.9% occurred in children over 10 years of age (57). There is no significant sex predilection.
Given their endocrine nature, islet cell tumors may or may not elaborate a hormonally active polypeptide, and this peptide product may or may not be capable of producing a clinical syndrome. It is not uncommon for tumors to produce more than one hormonal peptide, but clinical symptoms, if present, are related to one predominant hormone (8). Tumors that produce clinical syndromes are designated functioning or hyperfunctioning islet cell tumors. All others, even if they can be shown histologically to produce a peptide product, are called nonfunctioning or clinically silent islet cell tumors. The most common type of functioning islet cell tumor is the insulinoma (47% of functioning islet cell tumors), followed by gastrinoma (30%) (8). Other types of functioning and nonfunctioning islet cell tumors are exceedingly rare or have never been reported in children.
Clinical Features
The clinical presentation varies depending on whether the tumor produces a hormone-related syndrome and on the nature of the hormonal product.
Insulinoma.—
Insulinoma is composed of B or ß cells and causes fasting hyperinsulinemic hypoglycemia. Most patients have the Whipple triad of fasting hypoglycemia, symptoms of hypoglycemia, and immediate resolution of symptoms with intravenous administration of glucose. In young children, hypoglycemia commonly manifests as behavioral problems, seizures, or coma. These symptoms may be attributed to other causes, and diagnosis may be delayed. Untreated, recurrent hypoglycemia can lead to permanent neurologic sequelae (8).
Gastrinoma.—
Gastrinoma is composed of G cells and causes the Zollinger-Ellison syndrome. Patients frequently have multiple or recurrent peptic ulcers, classically in uncommon locations, such as the postbulbar duodenum and proximal jejunum (8,27). Gastroesophageal reflux and heartburn are also common symptoms. Gastric hypersecretion may cause diarrhea.
Other Functioning Islet Cell Tumors.—
All other functioning islet cell tumors are much less common in children. Adrenal corticotropic hormone–secreting islet cell tumor (ACTHoma) is a rare cause of Cushing syndrome. VIPoma is composed of D1 cells, secretes vasoactive intestinal peptide (VIP), and causes the Verner-Morrison or WDHA syndrome of massive watery diarrhea, hypokalemia, and achlorhydria. Most cases of VIP-producing tumors in children are not of pancreatic origin, as opposed to those in adults. According to Grosfeld et al (2), only two of 56 reported cases of pediatric VIP-producing tumors were pancreatic islet cell tumors. The rest were neurogenic tumors. Somatostatinoma is composed of D cells and causes a syndrome of diabetes mellitus, gallbladder disease, and steatorrhea. Glucagonoma is composed of A or cells and rarely causes a syndrome of diabetes mellitus, painful stomatitis, and a characteristic skin rash, necrolytic migratory erythema. To our knowledge, the last two have never been reported in a child (27).
Nonfunctioning Islet Cell Tumors.—
Nonfunctioning tumors commonly manifest late with symptoms due to mass effect, local invasion, or metastatic disease. The mean age at presentation is 70 years, except when associated with MEN 1, in which they occur in younger patients (8).
Pathologic Features
Tumor Size.—
Overall, neuroendocrine tumors vary widely in size, from 0.5 mm to 20 cm, but the size of a particular tumor at presentation reflects its tendency to produce clinical symptoms and the severity and specificity of those symptoms. Nonfunctioning islet cell tumors manifest late due to mass effect and are significantly larger than functioning islet cell tumors. Most patients with insulinoma have striking clinical symptoms and present with relatively small tumors, with mean diameter in the range of 2–2.2 cm (58,59) (Fig 4). Insulinomas are usually less than 3 cm in size unless malignant (8). In contrast, very few glucagon-producing tumors are associated with a clinical syndrome, and these are much larger at presentation, with a mean diameter of 7.6 cm (8).
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Figure 4a. Insulinoma in a 9-year-old girl with unexplained seizure disorder who had hypoglycemia immediately after a recent seizure. (a) Contrast-enhanced CT scan shows a small, homogeneous, intensely enhancing mass (arrow) in the body and tail of the pancreas. (b) Photograph of the resected specimen shows the well-circumscribed tumor, which has protuberant red and yellow areas on the cut surface but no cystic spaces. (c) Photomicrograph (original magnification, x16; H-E stain) shows sheets of small uniform cells (arrows), which are separated into lobules by intervening fibrovascular stroma (arrowheads). (d) Photomicrograph (original magnification, x40; insulin stain) shows brown-staining insulin-producing cells in a trabecular pattern. (e) Photomicrograph (original magnification, x40; Congo red stain) obtained under polarized light shows apple-green birefringence (arrows), which is indicative of amyloid in the stroma, thus allowing a specific diagnosis of insulinoma.
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Figure 4b. Insulinoma in a 9-year-old girl with unexplained seizure disorder who had hypoglycemia immediately after a recent seizure. (a) Contrast-enhanced CT scan shows a small, homogeneous, intensely enhancing mass (arrow) in the body and tail of the pancreas. (b) Photograph of the resected specimen shows the well-circumscribed tumor, which has protuberant red and yellow areas on the cut surface but no cystic spaces. (c) Photomicrograph (original magnification, x16; H-E stain) shows sheets of small uniform cells (arrows), which are separated into lobules by intervening fibrovascular stroma (arrowheads). (d) Photomicrograph (original magnification, x40; insulin stain) shows brown-staining insulin-producing cells in a trabecular pattern. (e) Photomicrograph (original magnification, x40; Congo red stain) obtained under polarized light shows apple-green birefringence (arrows), which is indicative of amyloid in the stroma, thus allowing a specific diagnosis of insulinoma.
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Figure 4c. Insulinoma in a 9-year-old girl with unexplained seizure disorder who had hypoglycemia immediately after a recent seizure. (a) Contrast-enhanced CT scan shows a small, homogeneous, intensely enhancing mass (arrow) in the body and tail of the pancreas. (b) Photograph of the resected specimen shows the well-circumscribed tumor, which has protuberant red and yellow areas on the cut surface but no cystic spaces. (c) Photomicrograph (original magnification, x16; H-E stain) shows sheets of small uniform cells (arrows), which are separated into lobules by intervening fibrovascular stroma (arrowheads). (d) Photomicrograph (original magnification, x40; insulin stain) shows brown-staining insulin-producing cells in a trabecular pattern. (e) Photomicrograph (original magnification, x40; Congo red stain) obtained under polarized light shows apple-green birefringence (arrows), which is indicative of amyloid in the stroma, thus allowing a specific diagnosis of insulinoma.
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Figure 4d. Insulinoma in a 9-year-old girl with unexplained seizure disorder who had hypoglycemia immediately after a recent seizure. (a) Contrast-enhanced CT scan shows a small, homogeneous, intensely enhancing mass (arrow) in the body and tail of the pancreas. (b) Photograph of the resected specimen shows the well-circumscribed tumor, which has protuberant red and yellow areas on the cut surface but no cystic spaces. (c) Photomicrograph (original magnification, x16; H-E stain) shows sheets of small uniform cells (arrows), which are separated into lobules by intervening fibrovascular stroma (arrowheads). (d) Photomicrograph (original magnification, x40; insulin stain) shows brown-staining insulin-producing cells in a trabecular pattern. (e) Photomicrograph (original magnification, x40; Congo red stain) obtained under polarized light shows apple-green birefringence (arrows), which is indicative of amyloid in the stroma, thus allowing a specific diagnosis of insulinoma.
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Figure 4e. Insulinoma in a 9-year-old girl with unexplained seizure disorder who had hypoglycemia immediately after a recent seizure. (a) Contrast-enhanced CT scan shows a small, homogeneous, intensely enhancing mass (arrow) in the body and tail of the pancreas. (b) Photograph of the resected specimen shows the well-circumscribed tumor, which has protuberant red and yellow areas on the cut surface but no cystic spaces. (c) Photomicrograph (original magnification, x16; H-E stain) shows sheets of small uniform cells (arrows), which are separated into lobules by intervening fibrovascular stroma (arrowheads). (d) Photomicrograph (original magnification, x40; insulin stain) shows brown-staining insulin-producing cells in a trabecular pattern. (e) Photomicrograph (original magnification, x40; Congo red stain) obtained under polarized light shows apple-green birefringence (arrows), which is indicative of amyloid in the stroma, thus allowing a specific diagnosis of insulinoma.
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Gastrinomas are slightly less capable than insulinomas and more capable than glucagonomas of producing clinical symptoms. Also, symptoms of gastrin hypersecretion are less remarkable than those of hyperinsulinism and may be incorrectly attributed to common gastroesophageal reflux. In addition, gastric hypersecretory diarrhea is occasionally the dominant symptom (60). These factors could cause clinical confusion and delay of diagnosis. This likely explains the larger mean diameter of gastrinomas at presentation (4.2 cm) compared to that of insulinoma (58). Furthermore, larger tumors are associated with more malignant behavior (58). Thus, 90% of insulinomas are benign, while only 20%–30% of glucagonomas are benign, and gastrinomas are in between, with 40% exhibiting benign behavior (8).
Tumor Location.—
Particular cell types of islet cell tumors vary in anatomic location. Sixty-five percent of insulinomas involve the body and tail of the pancreas (8,59). The vast majority of insulinomas occur in the pancreas, with less than 1% arising in extrapancreatic sites (8,57). On the other hand, gastrinomas and symptomatic nonfunctioning islet cell tumors have a predilection for the head of the pancreas, with the head involved in 71% of reported tumors (8).
Although gastrinomas most commonly arise in the pancreas, about 30% of gastrin-secreting tumors arise in extrapancreatic locations, including the duodenum, proximal jejunum, and stomach (8). Those involving the duodenum are often microadenomas, in the range of 1–2 mm in size (8). Despite their small size, duodenal gastrin-cell microadenomas may metastasize early to regional lymph nodes. The lymph node metastasis may be much larger than the duodenal primary, and the lymph node may be mistaken for the primary tumor (8). Unlike their pancreatic counterparts, gastrin-secreting tumors of the duodenum and proximal jejunum are mostly nonfunctioning (8), although those that do cause Zollinger-Ellison syndrome occur in younger patients.
In general, gastrinomas are found in the so-called gastrinoma triangle, bounded by the porta hepatis and the second and third portions of the duodenum. This triangle contains the head of the pancreas, the duodenum, peripancreatic soft tissues, and regional lymph nodes (8,27,61) (Fig 5).
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Figure 5a. Metastatic gastrinoma in an 8-year-old girl who presented with a several-month history of abdominal discomfort, chronic diarrhea, episodic vomiting, and black stools. Esophagogastroduodenoscopy revealed erosions and an ulcer in the gastric fundus and nodularity and two ulcers in the duodenum. Laboratory studies revealed no Helicobacter pylori and an elevated serum gastrin level. (a) Reformatted coronal image from CT arteriography shows an irregular but homogeneously enhancing mass in the region of the pancreatic head (straight arrow), a small enhancing mass in the left lobe of the liver (arrowhead), and thickening of gastric rugal folds (curved arrow). (b, c) Coronal single-photon-emission CT (SPECT) images from somatostatin receptor scintigraphy performed with indium 111–pentetreotide show localization of the radiopharmaceutical in the regions of the pancreatic head (straight solid arrow) and the left lobe of the liver (curved arrow in c), which correspond to the foci of abnormality on the CT image. The activity in the gallbladder (arrowhead in b) and kidney (open arrow in c) is physiologic.
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Figure 5b. Metastatic gastrinoma in an 8-year-old girl who presented with a several-month history of abdominal discomfort, chronic diarrhea, episodic vomiting, and black stools. Esophagogastroduodenoscopy revealed erosions and an ulcer in the gastric fundus and nodularity and two ulcers in the duodenum. Laboratory studies revealed no Helicobacter pylori and an elevated serum gastrin level. (a) Reformatted coronal image from CT arteriography shows an irregular but homogeneously enhancing mass in the region of the pancreatic head (straight arrow), a small enhancing mass in the left lobe of the liver (arrowhead), and thickening of gastric rugal folds (curved arrow). (b, c) Coronal single-photon-emission CT (SPECT) images from somatostatin receptor scintigraphy performed with indium 111–pentetreotide show localization of the radiopharmaceutical in the regions of the pancreatic head (straight solid arrow) and the left lobe of the liver (curved arrow in c), which correspond to the foci of abnormality on the CT image. The activity in the gallbladder (arrowhead in b) and kidney (open arrow in c) is physiologic.
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Figure 5c. Metastatic gastrinoma in an 8-year-old girl who presented with a several-month history of abdominal discomfort, chronic diarrhea, episodic vomiting, and black stools. Esophagogastroduodenoscopy revealed erosions and an ulcer in the gastric fundus and nodularity and two ulcers in the duodenum. Laboratory studies revealed no Helicobacter pylori and an elevated serum gastrin level. (a) Reformatted coronal image from CT arteriography shows an irregular but homogeneously enhancing mass in the region of the pancreatic head (straight arrow), a small enhancing mass in the left lobe of the liver (arrowhead), and thickening of gastric rugal folds (curved arrow). (b, c) Coronal single-photon-emission CT (SPECT) images from somatostatin receptor scintigraphy performed with indium 111–pentetreotide show localization of the radiopharmaceutical in the regions of the pancreatic head (straight solid arrow) and the left lobe of the liver (curved arrow in c), which correspond to the foci of abnormality on the CT image. The activity in the gallbladder (arrowhead in b) and kidney (open arrow in c) is physiologic.
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Ninety percent of insulinomas and the majority of sporadic gastrinomas are solitary (57). Multiple islet cell tumors are the rule in MEN 1, so the finding of multiple pancreatic neuroendocrine tumors should prompt an evaluation for this condition (26,57,62).
Gross Features.—
Islet cell tumors are round or ovoid, well-demarcated tumors with expansile growth patterns. Most small tumors are homogeneous, and many larger tumors are cystic, necrotic, or hemorrhagic. Occasionally, small calcifications are found in larger tumors (8,60). Smaller tumors are unencapsulated and larger tumors have a fibrous pseudocapsule. The pseudocapsule is often incomplete, and this finding should not be mistaken for invasive behavior. Consistency varies from soft to firm or rubbery, depending on the relative content of fibrous stroma.
Histologic Features.—
Generally, islet cell tumors are composed of sheets or nests of monomorphic medium-sized cells (Fig 4). These may be arranged in three different patterns as follows: (a) trabecular with or without gyriform arrangement; (b) acinar or glandular pattern, often surrounding a lumen; and (c) medullary or solid pattern. One pattern may predominate in one cell type of tumor or in benign versus malignant tumors, but the cellular pattern does not reliably predict the cell type or the biologic behavior of the tumor. Mitoses are unusual, even in tumors that behave aggressively (58).
The amount of intervening stroma is variable and affects the gross appearance of the tumor as well as the imaging findings. The stroma may be quite dense or appear hyalinized. Numerous blood vessels in the stroma impart the hypervascular nature characteristic of islet cell tumors. The finding of amyloid, which shows green birefringence under polarized light and stains for Congo red, is highly suggestive of insulinoma.
The biologic behavior of islet cell tumors is difficult to predict. Approximately 10% of insulinomas, 60% of gastrinomas, and most other functional islet cell tumors are malignant (2). In general, primary tumors that display malignant behavior are larger than benign tumors (mean diameter, 6.4–7.4 cm for malignant vs 1.7–2.9 cm for benign tumors) (58). Although almost all tumors 2 cm or less in size exhibit
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Abstract
LEARNING OBJECTIVES FOR TEST...
