abdominal mesothelial cyst

The lesions are unifocal and multifocal.

The lesions are located on the surface of the peritoneum in the cul de sac, on the intestines, urinary bladder, uterine adnexa, also involved round ligament within the pelvis and in the inguinal canal.

Additionally, small cysts, free-floating in the peritoneal cavity can be present.

Gross appearance

 The lesions can be polycystic.
 The surgical materials range from three fragments measuring 0.5 cm each to seven fragments, with the maximum size of 14x6 cm.
 The cysts are from microscopic size to 2 cm in diameter.
 The majority are thin-walled, semitranslucent, filled with clear or yellowish fluid or gelatinous contents.
 In some cases, the cyst walls are thicker and show intense inflammatory lesions and fibrinous exudate.

Microscopy

 The majority of cysts are lined with a single layer of flattened or cuboid mesothelial cells (CK+, calretinin+).
 In some patients, the mesothelium demonstrated diffuse squamous cell metaplasia.
 Sometimes, the cells focally form small papillae and are vacuolated.
 No mucus is observed either in the cytoplasm or outside the cells.

Immunochemistry

 Immunohistochemical reactions to CEA, ER, PR and MIB-1 are negative.
 Intramural proliferations and intracystic detached clumps of cells showed both mesothelial cells (without any mitotic activity and signs of atypia) and macrophages (CD68+).

Types

 unifocal
 multifocal

Localization

 diaphragmatic mesothelial cysts
 peritoneal surface (surface of the peritoneum)

• peritoneal cul-de-sac
• intestines
• urinary bladder
• uterine adnexa
• round ligament within the pelvis
• inguinal canal
• free-floating cysts in the peritoneal cavity

 visceral

• intra-hepatic mesothelial cysts (12489001)
• splenic mesothelial cysts

Synopsis

 Gross appearance: polycystic lesions
 Size: microscopic size to 2 cm in diameter
 thin-walled, semitranslucent, filled with clear or yellowish fluid or gelatinous contents
 cysts were with a single layer of flattened or cuboid mesothelial cells (CK+, calretinin+)
 diffuse squamous cell metaplasia
 cells focally forming small papillae
 vacuolated cells
 no mucus

Immunohistochemistry

 CK +
 calretinin +

Associations

 diaphragmatic defect (diaphragmatic hernia)

References

 Mesothelial inclusion cysts (so-called benign cystic mesothelioma)—a clinicopathological analysis of six cases. Urbańczyk K, Skotniczny K, Kuciński J, Friediger J. Pol J Pathol. 2005;56(2):81-7. PMID: 16092670

 Arber DA, Strickler JG, Weiss LM. Splenic mesothelial cysts mimicking lymphagiomas. Am J Surg Pathol. 1997 Mar;21(3):334-8. PMID: 9060604