- Pictorial Review
- Open Access
Part 1: CT characterisation of pancreatic neoplasms: a pictorial essay
© European Society of Radiology 2011
- Received: 11 January 2011
- Accepted: 4 May 2011
- Published: 18 May 2011
The pancreas is a site of origin of a diverse range of benign and malignant tumours, and these are frequently detected, diagnosed and staged with computed tomography (CT). Knowledge of the typical appearance of these neoplasms as well as the features of locoregional invasion is fundamental for all general and abdominal radiologists. This pictorial essay aims to outline the characteristic CT appearances of the spectrum of pancreatic neoplasms, as well as important demographic and clinical information that aids diagnosis. The second article in this series addresses common mimics of pancreatic neoplasia.
- Pancreatic neoplasms
- Computed tomography
Imaging of the pancreas is typically achieved with dual- or triple-phase acquisitions. Imaging is performed in the non-contrast, arterial and delayed portal venous phases using rapid contrast agent administration at 3–5 ml/s, preferably delivered via a wide bore cannula. High-density oral contrast agent interferes with the delineation of vessels and it can also make appreciation of an arterially enhancing lesion more difficult. Oral administration of 500–700 ml water approximately 30 min before imaging time is a safe and effective way to achieve distension of the upper gastrointestinal tract . Water acts as a negative contrast agent, differentiating the duodenum from the adjacent pancreatic head. Positive oral contrast agent may also be administered as part of the imaging preparation 60 min before imaging if lower abdominal and pelvic delineation of bowel loops from adjacent structures is required. Post-resection imaging may require a positive contrast agent to differentiate bowel loops from fluid collections and to help identify anastomotic leaks.
Pancreatic ductal adenocarcinoma accounts for 90% of all pancreatic neoplasms. Most of the patients are over 60 years of age at diagnosis. It is a common malignancy in both men and women and has a low 5-year survival rate , reflecting the predominance of late diagnosis and low resection rates at presentation. These tumours grow rapidly and metastasise early and only 10-15% of patients have tumours that are potentially resectable at diagnosis . Presenting symptoms can include jaundice, weight loss and abdominal pain. Risk factors include chronic pancreatitis, diabetes mellitus and hereditary cancer syndromes. Given the significant morbidity and mortality of this malignancy, early detection and accurate determination of resectability are of vital importance.
The following computed tomography (CT) signs of vascular invasion all have specificities of over 90% for both arterial and venous invasion. Combinations of these signs provide even greater specificity [12–14]: (1) vessel embedded in tumour; (2) tumour contact with over 180° of vessel circumference; (3) vascular irregularity; (4) vascular stenosis or thrombosis.
A meta-analysis demonstrated that CT had a sensitivity of 91% and a specificity of 85% for diagnosing pancreatic adenocarcinoma outperforming magnetic resonance imaging (MRI) . CT has a sensitivity of 81% for determining resectability and a specificity of 82% . Other studies show a negative predictive value for resectability of 100% and a positive predictive value of 89% with no significant difference between systems of different generations . Differentiating post-operative inflammatory changes from tumour recurrence can also be challenging and serial imaging is frequently required .
Cystic pancreatic neoplasms range from benign to malignant, and although they may have diagnostic features on CT, often other techniques—such as ultrasound and MRI—are required for further evaluation. It is important to differentiate cystic neoplasm from non-neoplastic pancreatic cysts, which is discussed further in Part 2 of this series. Overall, cystic neoplasms of the pancreas are relatively uncommon, accounting for only 1% of all primary pancreatic neoplasms .
Previously referred to as serous cystadenomas, these tumours are further divided into microcystic and macrocystic (oligocystic) subgroups based on macroscopic variation.
Microcystic adenomas are rare benign pancreatic tumours that are more common in females and tend to occur in the 7th decade of life—therefore termed the ‘grandmother’ tumour . Despite the predilection for females, cases do occur in males. This can be helpful in differentiating these lesions from mucinous cystic neoplasms, as these almost never occur in males . Microcystic adenomas may be discovered incidentally or present with non-specific abdominal symptoms such as nausea or abdominal pain.
Microcystic adenomas occur slightly more commonly in the pancreatic head and can be so large that they almost completely replace the gland. They are differentiated from ductal adenocarcinoma by their typically large size (>10 cm), honeycombed appearance, hypervascularity and central scar . Serum tumour markers such as carcinoma embryonic antigen (CEA) and carbohydrate antigen (CA) 19.9 are typically within the normal range in cystic pancreatic neoplasms and elevation of these markers is also useful in distinguishing these lesions from ductal adenocarcinoma .
Macrocystic serous adenomas are a variant of the microcystic adenoma. They are always benign and are characterised by unilocular or bilocular cysts that are greater than 2 cm in size. Similar to microcystic adenomas, there is a female predominance and the tumours more frequently occur in patients over 50 years of age. With large cystic spaces, these tumours can be difficult to distinguish from mucinous cystic neoplasms . Generally, endoscopic ultrasound evaluation and aspiration are required to demonstrate a benign cytology and serous fluid rather than a mucinous aspirate.
Serous cystic neoplasms, in particular microcystic neoplasms, may present with symptoms of mass effect when large. Complications include obstruction of the second part of the duodenum and jaundice due to common bile duct obstruction. In these cases, complete tumour resection is the aim of management . For asymptomatic lesions, management is more controversial. Tumours greater than 4 cm in size are thought more likely to grow and eventually cause symptoms and this may be used as a criterion for prophylactic resection . Ultimately, this decision would involve a risk–benefit analysis of the patient’s age and medical comorbidities, as well as tumour size and location in the pancreas.
Mucinous cystic neoplasms are the most common cystic neoplasm and occur almost exclusively in middle-aged women, (the ‘mother’ tumour) . These tumours are potentially malignant (mucinous cystadenocarcinoma) and surgical resection is therefore the mainstay of treatment . Most are incidental findings with the remainder presenting with non-specific abdominal symptoms including weight loss in metastatic cases.
Compared with the serous cystic neoplasms, cyst fluid CEA is elevated in mucinous cystic tumours and the degree of elevation correlates with the diagnosis of mucinous cystadenocarcinoma or mucinous cystadenoma with malignant potential . Serum tumour markers CA 125 and CA 72–4 are also suggestive of a malignant or pre-malignant lesion .
Intraductal papillary mucinous neoplasm (IPMN) is a low-grade malignancy that more frequently occurs in elderly patients with a male predominance (the ‘grandfather’ tumour). The tumour arises from a proliferation of the pancreatic ductal epithelium and may be predominantly cystic or papillary in composition. There is resultant excess mucin production and progressive dilatation of the main pancreatic duct or cystic dilatation of the branch ducts. These lesions frequently present with pancreatitis, abdominal pain or jaundice .
Main duct type—moderate or marked dilatation of the main pancreatic duct
Segmental—can occur in the body or tail with upstream dilatation of the duct only
Branch duct type—most frequently in the uncinate process and appears as round or oval lobulated masses
Diffuse type—homogeneous low density appearance and differentiation from chronic pancreatitis can be difficult
Although frequently benign, they may contain carcinoma in situ or be frankly malignant with features of malignant degeneration including irregularity of the wall and thick septa with solid nodules . Similar to mucinous cystic neoplasms, IPMN cyst fluid analysis shows high CEA and CA 72–4. A point of difference is high amylase in IPMN . Elevated serum CEA and CA 125 are also associated with malignant lesions . The best predictor of malignant potential, however, is tumour location, with the main duct type having a 70% chance of harbouring malignancy compared with 25% for the branch duct type . All main duct type IPMN are recommended for resection, whereas branch duct type IPMN less than 3 cm in size and lacking mural nodules could potentially be managed conservatively .
Also sometimes referred to as solid pseudopapillary tumours (SPT), solid and papillary epithelial neoplasms (SPEN), or Frantz’s tumours, these tumours occur in young women in the 2nd and 3rd decades of life (the ‘daughter’ tumour), and are of fairly low malignant potential . Metastases or vascular invasion may complicate 10–15% of cases; however, long-term survival is common in these patients following surgery and chemotherapy . Complete surgical excision is always recommended, not only because of malignant potential but also because of the considerable size to which these tumours can grow. SPPNs begin as solid masses with a delicate internal vasculature. As the lesion enlarges, haemorrhagic and cystic degeneration occurs, with only the cells close to the small vessels remaining intact .
Neuroendocrine tumours, or islet cell tumours, account for 1–5% of all pancreatic neoplasms and arise from the endocrine pancreas . Patients are typically in their 50s, with a slight male predominance. Most are solitary lesions that arise sporadically, but neuroendocrine tumours may also occur as part of genetic syndromes, such as multiple endocrine neoplasia type 1 (MEN 1), von Hippel-Lindau, neurofibromatosis type 1 and tuberous sclerosis. Neoplasms in these conditions are often multiple, particularly in MEN 1.
Islet cell tumours are also classified as functional and non-functional, depending on whether the cells actively secrete hormones. The functional lesions present with classic clinical syndromes, depending on the cell type, and tend to be less than 3 cm in size at diagnosis because of systemic symptoms leading to presentation, while non-functioning tumours are more likely to present with symptoms of mass effect [37, 38]. Functional tumours include insulinomas (present with hypoglycaemia) and gastrinomas (present with peptic ulcer disease in Zollinger-Ellison Syndrome, and typically arise in the gastrinoma triangle bounded by the junction of the cystic duct insertion to the common bile duct, the body of the pancreas, and the junction of the second and third portions of the duodenum), glucagonomas (present with diabetes, anaemia, weight loss and rash), VIPomas (presents with WDHA syndrome (watery diarrhoea, hypokalaemia, achlorhydria) and somatostatinomas (present with diabetes, cholelithiasis and steatorrhoea).
Neuroendocrine lesions do not characteristically show calcification and as lesions grow they develop cystic or necrotic areas. The periphery of the lesion will continue to arterially enhance . Local vascular encasement or invasion, which is commonly seen with ductal adenocarcinoma, is rarely seen with neuroendocrine tumours . Arterial phase imaging of the liver is vital to detect hepatic metastases.
Primary lymphoma of the pancreas is rare. Secondary involvement can occur via direct extension from the retroperitoneum. Symptoms are typical of those of systemic lymphoma and jaundice is rare, even with large masses at the pancreatic head.
Metastases to the pancreas are rare, found in only 3–12% of patients at autopsy with advanced malignancy . The most frequent primary lesions are bronchogenic carcinoma and renal cell carcinoma. Other documented sources are breast, thyroid, melanoma, gastrointestinal tract and hepatocellular carcinoma .
As demonstrated, the spectrum of pancreatic neoplasms has varying age and gender profiles as well as clinical presentations. This information, coupled with knowledge of the typical CT characteristics, allows for reasonable confidence in diagnosis. Multiphase CT, with the range of post-processing techniques available, also plays a crucial role in determining the resectability of pancreatic ductal adenocarcinoma, the most common pancreatic neoplasm.
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