With increased cross-sectional imaging, many cystic pancreatic lesions are found incidentally. For example, 13.5% of asymptomatic patients undergoing abdominal MRI will have incidentally detected cystic pancreatic lesions, usually small (7 mm), solitary (60%), and with an increasing incidence with age (Lee et al). Many of these small lesions are presumed branch duct IPMNs, although some may represent non-neoplastic cysts (mucinous, lymphoepithelial, or epithelial).

Larger and more complex lesions often are surgically resected, and radiologists are only 60-63% accurate in providing the correct diagnosis pre-operatively (Correa-Gallego et al, Del Chiaro et al). Increasing our awareness of these lesions and their MRI phenotype can decrease unnecessary EUS and possibly morbid pancreatic surgery. This image-rich talk will focus on these potentially surgical lesions, and how to use their MRI phenotypes to narrow the differential diagnosis.

The seven cystic pancreatic lesions to be covered can be divided into two broad categories - primarily cystic lesions and solid lesions undergoing cystic change. Primarily cystic lesions include intraductal papillary mucinous neoplasm (IPMN), mucinous cystic neoplasm (MCN), pseudocyst and serous cystadenoma (SCA). Solid lesions undergoing cystic change include cystic neuroendocrine tumor (NET), necrotic adenocarcinoma, and solid pseudopapillary tumor (SPT).

The patient's clinical history and demographics are important factors in narrowing the differential diagnosis of cystic pancreatic neoplasms. Gender and age are most helpful for MCN (95% female, middle-aged), SPT (88% female, young) and SCA (75% female, older). A convincing history of pancreatitis can suggest a diagnosis of pseudocyst.

Cyst fluid analysis obtained during EUS cyst fluid aspiration can narrow the differential. A cyst fluid CEA > 192 ng/mL yields a 73% sensitivity and 84% specificity for mucinous lesions such as MCN and IPMN (Brugge et al). Elevated amylase suggests communication with the pancreatic duct, such as IPMN and pseudocyst. Recent studies have shown that cyst fluid VEGF-A levels > 8500 pg/mL yield a 100% sensitivity and 97% specificity for SCA (Yip-Schneider et al).

1. Branch Duct IPMN

- Lesion morphology: tubular / ovoid > round; communication with duct; 40% multifocal (“field defect”); main duct involvement is under called in 20% of cases (Correa-Gallego et al)

- 2012 International Consensus Guidelines (Tanaka et al): Worrisome features include size > 3 cm, thickened/enhancing walls, main duct 5-9 mm, non-enhancing mural nodule, abrupt change in duct caliber

- High risk stigmata of malignancy: obstructive jaundice, enhancing solid component, main duct > 10 mm

- Small FOV DWI can help w/ detection of invasive component

- Additional: Older, slight male predilection, EUS CEA > 192, elevated amylase

2. Mucinous Cystic Neoplasm (MCN)

- Lesion characteristics: thin wall, clean claw sign with pancreas; +/- enhancing septations or locules; typically not T1 hyperintense unless post-biopsy; +/- peripheral calcification on CT; can be unilocular (look for nice claw sign to ddx from pseudocyst); predilection for body/tail. Size > 4 cm and enhancing soft tissue component suggests carcinomatous transformation

- Additional: Middle-aged, female (95%) as lined by ovarian stroma, EUS CEA > 192, no elevation in amylase

3. Pseudocyst *most common cystic lesion of the pancreas

- Lesion characteristics: T1 hyperintense internal debris / hemorrhage (sometimes with a fluid-fluid level); no internal enhancement; thick T2 hypointense wall which becomes more discrete over time; dissection of inflammatory tissue along fascial planes; evidence of acute/chronic pancreatitis elsewhere in gland; obliteration of venous structures

- Most helpful clue is history and prior imaging showing an evolution of pancreatitis

4. Serous Cystadenoma (SCA)

- Lesion characteristics: Lobulated / bosselated border; typically microcystic honeycomb appearance with thin enhancing septations, but also can be oligocystic (10%), mixed micro/macrocystic, and solid variant; can obstruct duct; only 30% with pathognomonic central scar (enhancing or T2 hypointense calcification). -

- DWI may be able to differentiate between mucinous cysts and SCA with 100% sensitivity and 97% specificity (Schraibman et al)

- EUS: VEGF-A > 8500 is 97% specific; also cystic fluid metabolites glucose and kynurenine are markedly elevated in SCA compared to MCNs

- Can occur in VHL patients – look for other VHL lesions such as RCC

- Benign – NO malignant potential (30 cases reported in literature, but most pathologists do not believe that SCA has malignant potential) so accurate pre-operative diagnosis prevents surgery

5. Cystic components found in 17% of resected NET

- Lesion characteristics: well circumscribed; rim of well-vascularized tissue; centrally can be completely cystic or have low level internal enhancement amongst degeneration

- Usually non-functional, lower grade / better prognosis than solid nonfunctioning NET

- More correlated with Multiple Endocrine Neoplasia (MEN) than patients with solid NET

6. Necrotic Adenocarcinoma

- Lesion characteristics: infiltrative mass w/ cystic component from necrosis, side-branch obstruction, or adjacent pseudocyst; usually causes ductal obstruction

- Main DDX: invasive adenocarcinoma in the setting of an IPMN, necrotic collection

7. Solid Pseudopapillary Tumor (SPT)

- Lesion characteristics: well circumscribed, large (avg size 9 cm), solid / papillary / hemorrhagic (T1 hyperintense) / pseudocystic mass in pancreatic tail (60%) of young (29 yo) female (88%)

- Low grade malignant potential, excellent prognosis

- Main DDX: MCN w/ invasive component, cystic NET --> all three are surgical lesions so may not change management

1. Calling a pseudocyst because “history of pancreatitis”, final pathology reveals MCN

Teaching point: History of pancreatitis can be a red herring, look at remaining gland for any signs of prior pancreatitis. A thin wall and clean claw sign with no additional signs of acute/chronic pancreatitis suggests MCN. Non-enhancing T1 hyperintensity, a thickened rind and evolution over several exams suggests a pseudocyst.

2. Calling a lobulated oligocystic lesion w/ central confluent enhancement an IPMN with enhancing nodule, when it is actually oligocystic or mixed micro/macrocystic SCA

Teaching point: If lobulated / bosselated border and possible central scar, recommend EUS w/ VEGF-A – can prevent unnecessary surgery.

3. Calling an oligocystic lesion an MCN (surgical lesion) when it is an IPMN (not necessarily surgical lesion depending on size).

Teaching point: If solitary lesion in middle aged female, favor MCN. If additional small cysts, tubular, or connection to duct, favor IPMN. If still overlap, consider EUS.

4. Assuming men cannot get SPT (12% will be in men) or MCN (at least 5% will be men)

Teaching point: If it looks like a possible SPT or MCN, put it in the differential because different pathologic stains will be performed on EUS-FNA.

5. Calling a small-moderate sized lesion an SPT because the patient is young and female, without looking as carefully at the lesion, which could possibly be a cystic NET.

Teaching point: Smaller SPTs are being found more frequently / incidentally with increased imaging (not necessarily large). SPTs have areas of hemorrhage in an overall solid mass; cystic NET tends to have a peripheral rind of enhancement and are associated with MEN syndrome.

6. Calling a main duct IPMN w/ solid components when it is chronic pancreatitis or vice versa.

Teaching point: Chronic pancreatitis can overlap with main duct IPMN – look carefully at their history, any prior CTs with calcification, EUS findings suggesting calcifications and fibrosis, main duct irregularity. Check diffusion for focal mass.

7. Calling pancreatitis and walled-off necrosis in setting of necrotic adenocarcinoma causing inflammation

Teaching point: Pancreatic adenocarcinoma can cause pancreatitis and necrotic pancreatic adenocarcinoma can mimic a complex pseudocyst / walled off necrosis. Look carefully at any cases of unexplained pancreatitis, for an obstructing or necrotic mass.

8. Calling a branch-duct IPMN when it is pathologically confirmed to be a benign lesion

Teaching point: 5% of resected pancreatic cystic lesions will be benign cysts (lymphoepithelial cysts, squamoid cysts, mucinous non-neoplastic cysts, non-classified cysts), but currently there are no specific / defining features to differentiate.