Cystic tumors

Pancreatic cystic tumors account for about 5% of pancreatic neoplasms. They also include cystic dilatations of intraductal neoplasms, cystic degenerations of solid neoplasms (solid-pseudopapillary tumor), and solid neoplasms with focal cystic change (ductal adenocarcinoma with cystic degeneration, cystic acinar cell carcinoma, cystic pancreatic endocrine tumor).

Serous cystadenoma

It usually occurs in elderly women, most often in the body and tail of the pancreas. It is usually benign, although rare cases of serous cystadenocarcinoma have been reported. Star-burst calcifications within a central scar can be diagnostic on imaging when present. Most tumors are ‘microcystic’ with multiple, <2cm cysts, but can be unilocular due to specific variant or due to haemorrhagic degeneration, causing problems with imaging diagnosis.

Cytologic preparations are characterized by low cellularity and the cells are arranged in small clusters or flat sheets. The cytoplasm is clear or vacuolated and the nuclei are small and round. The presence of glicogen is demonstrated by PAS positivity.

Cytologic diagnostic features

Watery, non-mucinous fluid
Scanty cellularity
Clean, proteinaceous or bloody background
Monolayered sheets or small, flat clusters
Bland, uniform, round nuclei
Scanty but visible non-mucinous cytoplasm

Differential diagnosis

Benign ductal or acinar epithelium
Lymphangioma/hemangioma
Mucinous cystic neoplasm
Cystic pancreatic endocrine tumor
Metastatic renal cell carcinoma

Mucinous cysts of the pancreas

WHO classification

Mucinous cystic neoplasm
- Mucinous cystadenoma
- Borderline mucinous cystic neoplasm
- Mucinous cystadenocarcinoma
Intraductal papillary mucinous neoplasm
- Intraductal papillary mucinous adenoma
- Intraductal papillary mucinous neoplasm of borderline malignancy
- Intraductal papillary mucinous carcinoma
- Intraductal papillary mucinous neoplasm with invasive carcinoma: tubular type or colloid carcinoma

Mucinous cystic neoplasms

They usually arise in women in the fourth and fifth decades, mostly in the pancreatic tail. They encompass a spectrum ranging from benign to low malignant potential to frankly malignant. The cytomorphology of mucinous epithelium does not reliably predict biologic behaviour.

They are lined by mucinous epithelium which is generally non-papillary, but can also be focally papillary. In women they can show a subepithelial ‘ovarian-like’ stroma. The cysts do not communicate with the pancreatic ductal system and may contain thin septae.

Cytologic diagnostic features

Abundant background mucin and muciphages
Columnar mucinous cells in sheets, papillae and single cells
Varying degrees of nuclear and architectural atypia
Nuclear pseudostratification
Nuclear enlargement, crowding or overlapping
Complex papillary groups

Both intra- and extracellular mucin are highlighted by a mucicarmine stain.

Mucinous cystadenocarcinoma – cytologic diagnostic features

High cellularity
Abundant background mucin
Increased cellular dyshesiveness
Marked nuclear atypia (enlargement, anisonucleosis, macronucleoli)
Signet ring cells
Numerous mitoses
Necrosis

Intraductal papillary mucinous neoplasm

This tumor is characterized by a primarily intraductal growth and its cytomorphology encompasses a spectrum ranging from benign to frankly malignant. It may grow diffusely along the entire length of the duct and its branches, or form focal complex papillary proliferations. The cytologic features are similar to those of mucinous cystic neoplasms. Necrosis, mitoses and marked nuclear atypia lead to a diagnosis of papillary mucinous carcinoma.