Classification

The cystic pancreatic lesions can be classified as:
1.    Mucinous cystic neoplasms (30%)
2.    Non mucinous cystic neoplasms (40%)
3.    Pseudocysts (30%)
Mucinous cystic neoplasms present intermediate malignant potential therefore resection is recommended. On the other hand resection is not mandatory for non mucinous cystic neoplasms that present low or no malignant potential and for pseudocysts.

Approach to the Pancreatic Cysts: The Problems

• Half of these lesions are asymptomatic and incidentally discovered at the time of imaging for other reasons.

• It is unlikely that any combination of clinical and radiological parameters can accurately make the important distinction between mucinous and non-mucinous cystic pancreatic lesions.

• Pancreatic surgery carries significant morbidity. If resection is performed for all incidentally discovered cystic pancreatic lesions, there is the potential to harm patients for whom the malignant risk is negligible [1].

Imaging features- morphologic types

Incidentally discovered pancreatic cysts are classified into four gross morphologic types based solely on imaging appearance at MDCT [2]:

• Unilocular (pseudocysts, lymphoepithelial cysts, small IPMTs)

• Microcystic (serous cystadenoma)

• Macrocystic (mucinous cystic tumor, IPMTs)

• Cysts with a solid component (solid pseudopapillary neoplasm, MCN).

The radiologist to make his report is based on the following features:

• presence or absence of septa/loculations

• presence and location of calcification

• location of the mass within the pancreas

• presence of main pancreatic duct involvement

• presence of mural nodules or papillary proliferations

The importance of the pancreatic cyst size

• Small cysts (closer to 1 cm) are more likely to be benign.

• Cysts of this size are frequently detected at MRI but they are not easily characterized through imaging.

• Size alone cannot be an independent decision making variable.

• Radiologists must attempt to exclude the presence of morphologic abnormalities that raise the suspicion of a complex cyst (mural nodules, dilatation of the common bile duct, dilatation of the main pancreatic duct larger than 6 mm, duct wall enhancement, lymphadenopathy, peripheral calcifications).  

The importance of the patient symptoms

• 90% of patients with malignant cystic lesions are symptomatic.

• In asymptomatic patients with pancreatic cysts smaller than 3 cm, the incidence of occult malignancy is  3.3%

• The presence or absence of patient symptoms (eg, weight loss, jaundice, diabetes, anorexia) is a critical component of the management decision.

Criteria used for follow-up

• Cystic lesion size < 3 cm

• no mural nodules

• no papillary proliferations

• no main pancreatic duct dilatation

• asymptomatic patient

Examples in daily practice

A radiologist could face the following diagnoses during interpretation of an incidentally discovered pancreatic cyst:

1. A certain diagnosis (microcystic adenoma) (fig. 1, 2)

2. An uncertain diagnosis (macrocystic lesion-MCN) (fig. 3, 4)

3. A likely diagnosis (main duct type IPMN) (fig. 5)

4. A questionable diagnosis that needs more imaging tests to be confirmed (branch duct type IPMN) (fig. 6, 7)

5.  An easy diagnosis but only when features are typical (SPEN) (fig. 8, 9, 10)

6. A rare diagnosis (neuroendocrine cystic neoplasm, lymphoepithelial cysts) (fig. 11, 12)

7.  An unexpected diagnosis (pancreatic metastasis) (fig. 13, 14)

8.  An impossible diagnosis (very small cyst) (fig. 15, 16)

The role of EUS-FNA of Pancreatic Cyst Fluid

• Cytologic examination of cyst fluid has been proven insensitive (few exfoliated cells in the cyst).  

• More helpful: Analysis of cyst fluid for tumor markers.

• Surprisingly, CA 19-9 has not been helpful [3].

• CEA>480ng/mL and viscosity>1.6: accurately predict MCN

• CEA>6000ng/mL: indicates malignancy

Variation in recommendations - practice

A remarkable variation has been noticed in reporting, in management recommendations and finally in practice [4, 5].

• 83% of recommendation variation is the result of the preference or opinion of the individual radiologist.

• Variation in management recommendations can lead to under- or overtreatment.

• Variation in practice can lead to underuse, misuse, and overuse of care.

Guidelines

Several professional societies have developed guidelines for the management of pancreatic cysts. They reflect either an international consensus of gastroenterologists, surgeons, and pathologists, all of whom are recognized authorities in pancreatic imaging or proposals by a number of interested medical and surgical societies [6, 7].

Follow up frequency-Sendai guidelines

• <1cm: each year.

• 1-2cm: for 24 months at 6-month intervals and then yearly for a second 24 months declaring stability after 4 years.

• 2-3cm: every 3 to 6 months.

Follow up frequency - ACR guidelines [8]

• <2cm: a single follow-up in 1 year.

• 2-3cm: a follow-up of every 6 months for 2 years and then yearly for lesions.

MRI is the preferred follow up procedure (superior contrast resolution,  lack of radiation).

For patients older than 60 years, ionizing radiation issues may not be as compelling.
Care must be taken to assure that measurements are made carefully and consistently.

• >3cm: resect unless they are serous cystadenoma or proven to be pseudocyst through aspiration.

Conclusions

1. Increasing use of imaging has resulted in wider recognition of these lesions in asymptomatic individuals.

2. Risk of malignancy is determined in large part by distinction between mucinous (higher risk) and non-mucinous (no risk) subtypes.

3. Determination of CEA and amylase levels in cyst fluid aspirated by EUS-FNA is helpful in making the diagnosis.

4.  Diagnostic uncertainty often remains, leading to a final diagnosis at the time of surgical resection.

5.  Microsyctic adenoma is the only type of cystic neoplasm that can be diagnosed with almost complete certainty.

6.  Diagnosis of mucinous cystic tumors is often hypothetical.

7.  Small lesions are more susceptible to misdiagnosis.

8. Radiologists need to be familiar with published guidelines for the management of pancreatic cysts.