• Pancreatic serous cystic neoplasms account for approximately 20% of primary cystic pancreatic neoplasms1
• Most serous cystic neoplasms are benign and represent serous cystadenomas (SCAs)1
• Classically, serous cystadenomas have been described as multilocular well-circumscribed masses that contain a central stellate scar and calcifications2
• However, serous cystadenomas have a wide spectrum of CT appearance ranging from an unilocular cystic lesion to a solid hypervascular mass3

• The CT appearance of SCAs may overlap with potentially malignant cystic neoplasms such as mucinous cystic neoplasms and intraductal mucinous neoplasms (IPMNs)4
• Due to rarity of SCAs and variable CT appearance, accuracy of preoperative CT diagnosis has been reported to be as low as 23.3%5
• The predictive value of CT for diagnosis of SCAs improved with increasing number of detectors5
• Therefore, further characterization of CT features on dual-phase multidetector may improve diagnostic accuracy of SCAs

• To characterize morphologic features and CT attenuation of pancreatic serous cystadenomas on dual-phase multidetector CT
• To determine CT features which may be useful in differentiating serous cystadenomas from other pancreatic lesions
• To review the management implications

• Institutional review board approved retrospective study
• From January 2003 to December 2010, 68 patients with surgically resected and pathologically confirmed pancreatic serous cystadenomas were identified from the pathology database
• 68 patients had preoperative dual-phase multidetector CT examinations 40 female, 28 male, mean age 58
• CT examinations were performed on a 16-slice, 64-slice, or dual source multidetector CT

• +/- Septations
• +/- Calcifications
• +/- Peripheral rim enhancement
• +/- Main pancreatic duct (MPD) dilatation
• +/- Common bile duct (CBD) dilatation
• +/- Vascular invasion
• +/- Suspicious liver mass
• +/- Mesenteric lymphadenopathy

• Arterial phase:
  • Region of highest attenuation within the SCA
  • Region of lowest attenuation within the SCA
  • Background pancreas
• Portal venous phase:
  • Corresponding highest and lowest attenuation regions
  • Background pancreas

• 70 serous cystadenomas were identified in 68 patients
• Mean maximal axial dimension = 4.5 cm
  • Range: 1.0 cm to 12.2 cm
• Location:
  • Head (29%)
  • Neck (6%)
  • Body (27%)
  • Tail (39%)

• ~ Half of the calcifications were located centrally
• Less than half of the calcifications were located peripherally

• Vascular displacement due to mass effect was uncommon
• Vascular occlusion was rare

• Atrophy or fatty replacement of background pancreas (11%)
• No suspicious liver lesion
• No mesenteric lymphadenopathy

• Pancreatic SCAs were subdivided based on CT attenuation and morphologic features:
  • Oligocystic (9%)
    • < 6 cysts, each cyst > 2 cm
  • Polycystic (37%)
    • > 6 cysts, each cyst < 2 cm
  • Cystic and solid (34%)
    • Contains both soft tissue component and cystic component
  • Solid (20%)
    • Soft tissue attenuation without identifiable cysts

• “Classic” serous cystadenoma has been described as a cystic lesion with:2
  • Multiple thin non-enhancing septations
  • Central calcifications
  • Absence of main pancreatic duct dilatation
  • Absence of vascular involvement
• 20% of the cases fulfill this “classic” description

• “Classic” SCAs were generally larger in size: (p = 0.005)
  • Mean diameter of “classic” lesion = 6.3 cm
  • Mean diameter of “non-classic” lesion = 4.0 cm
• Higher percentage of larger SCAs demonstrated “classic” morphology
  • Lesion < 3cm: 7% with “classic” morphology
  • Lesion > 3cm: 29% with “classic” morphology

• Traditional classification of SCAs was based on imaging and gross pathologic features:3,6
  • Microcystic (70%)
  • Honeycomb (20%)
  • Oligocystic (<10%)
• Classification of SCAs based on CT attenuation and morphologic features:
  • Polycystic (37%)
  • Cystic and solid (34%)
  • Solid (20%)
  • Oligocystic (9%)

• The polycystic pattern and cystic and solid pattern fit into the microcystic category and represented the most common CT appearance of serous cystadenomas
• Most of the solid cystadenomas fit into the honeycomb category, in which the individual cysts were too small to be resolved on CT
• One of the solid cystadenomas was a rare solid variant of serous cystadenoma, which did not contain any cystic spaces on histopathology

• Pseudocyst 18.9 HU ± 3.8
• Mucinous cystic neoplasms 13 HU ± 2.5
• IPMNs 11.4 HU ± 2.7

• DDX: Mucinous cystic neoplasm, pseudocyst, IPMN
• External Contour:
  • External lobulations has been reported as a specific feature for SCAs4,8
    • 72% of oligocystic and polycystic SCAs demonstrated external lobulations
  • Mucinous cystic neoplasm: Smooth contour
  • Pseudocyst: Smooth contour
  • IPMN: Pleomorphic or clubbed fingerlike cystic shape
• Fibrous Central Scar ± Calcifications:
  • Highly specific and virtually path gnomonic for SCA6

• Pancreatic Duct:
  • SCA: No communication with pancreatic duct
  • IPMN: Communication with pancreatic duct
• CT Attenuation Values:
  • Similar to reported values for pseudocyst, mucinous cystic neoplasms, and IPMNs
• Clinical Information:
  • SCA: No history of pancreatitis
  • Pseudocyst: History of pancreatitis

• Yoon et al. (2011) reported mean CT attenuation values for pancreatic adenocarcinoma:9
  • Pancreatic parenchymal phase – 109.4 HU
  • Hepatic venous phase – 96.0 HU
• Liu et al. (2009) reported mean CT attenuation values for insulinomas:10
  • Arterial phase – 114.48 ± 27.30 HU
  • Portal venous phase – 112.19 ± 19.52 HU

• DDX: Adenocarcinoma, islet cell tumor, solid pseudopapillary tumor
• Pancreatic Duct and Common Bile Duct Dilatation:
  • SCA: Uncommon
  • Adenocarcinoma: Common
• Vascular Involvement:
  • SCA: May compress adjacent vessels due to mass effect, vascular occlusion rare
  • Adenocarcinoma: Vascular involvement frequently seen, important determinant in resectability

• Liver Metastasis and Mesenteric Lymphadenopathy:
  • Absent in SCAs
  • May be seen in serous cystadenocarcinoma (extremely rare)
  • Presence suggestive of adenocarcinoma or islet cell tumor
• CT Attenuation Values:
  • May overlap with adenocarcinoma and islet cell tumor
• Clinical Information:
  • Older age group than solid pseudopapillary tumor
  • Absence of symptoms associated with functioning islet cell tumor

• Important to differentiate serous cystadenoma from other malignant or premalignant lesions
• Management of SCAs depend on patients’ age and comorbidities, tumor size and location, presence or absence of symptoms, local practice patterns, and surgeon preferences5
• If diagnosis of SCA can be made based on imaging and laboratory findings, surgical resection is usually reserved for:11
  • Symptomatic patients
  • > 4cm in size regardless of symptoms

• However, many SCAs do not demonstrate “classic” imaging characteristics and remain indeterminate
• ACR Guidelines for management of pancreatic cystic lesions17:
  • < 2cm: Single follow-up in 1 year, no further follow-up if asymptomatic
  • 2 to 3 cm:
    • Mucinous: Follow-up every 6 months
    • Uncharacterized: Follow-up yearly
    • Serous cystadenoma: Follow-up every 2 years
  • > 3cm: Consider surgery
  • Endoscopic ultrasound and cyst aspiration may be useful adjuncts

• All cases of serous cystadenomas were surgically resected and pathologically proven
• All preoperative dual-phase multidetector CTs were performed with consistent technique, which allowed for:
  • Qualitative morphologic assessment
  • Quantitative CT attenuation measurements

• This retrospective surgical series may contain a higher proportion of atypical cases
  • Typical cases based on CT morphology may not be referred to surgery and were excluded
• CT acquisition and ROI measurement techniques were not the same as previous studies
  • We elected to measure regions with the highest and lowest attenuation due to the variability of attenuation within the same lesion
  • Limited comparison of CT attenuation among various pancreatic lesions

• “Classic” morphology of pancreatic serous cystadenoma was uncommon and only found in 20% of cases
• Most common CT appearance of serous cystadenoma was a polycystic or mixed cystic and solid mass
• Wide spectrum of CT appearances ranging from unilocular cyst to hypervascular solid mass

• Significant overlap in CT attenuation among serous cystadenoma and other cystic and solid pancreatic lesions
• Presence of external lobulations useful in differentiating serous cystadenomas from other cystic pancreatic lesions
• Absence of aggressive features useful in differentiating serous cystadenomas from solid malignant pancreatic lesions

1. Basturk O, et al. Arch Pathol Lab Med 2009;133:423-438
2. Curry CA, et al. AJR 2000;175:99-103
3. Kim HJ, et al. AJR 2008; 190:406-412
4. Kim SY, et al. AJR 2006; 187:1192-1198
5. Khashab MA, et al. Am J Gastroenterol 2011; 106:1521-1526
6. Sahani DV, et al. Radiographics 2005; 25:1471-1484
7. Chalian H, et al. JOP 2011; 12:384-388
8. Cohen-Scali F, et al. Radiology 2003; 228:727-733
9. Yoon SH, et al. Radiology 2011; 259-442-452
10. Liu Y, et al. Radiol Med 2009; 114:1232-1238
11. Berland LL, et al. J Am Coll Radiol 2010; 7:754-773

Acknowledgements

• LC Chu, MD
• AD Singhi, MD PhD
• RH Hruban, MD
• EK Fishman, MD