Chapter 9 Answers to self-check questions

Serous effusions and peritoneal washings

9.1 What is the function of serous fluid and how is it produced?

Serous fluid acts as a lubricating fluid, which allows movement of the organs in the body cavity such as the beating of the heart, movement of the bowel, and expansion and contraction of the lungs. The fluid is formed by filtration of plasma through the capillary endothelium.


9.2 What is the difference between an exudate and a transudate?

Transudates have low protein and low specific gravity (density). The cellular content of transudates is generally low. Transudates are caused by an imbalance of hydrostatic and oncotic pressure and are associated with kidney, heart, or liver failure, or hypoalbuminemia. Exudates have higher protein content and specific gravity. They are caused by the increased permeability of capillaries, which can occur when the serous membranes are damaged by a disease process. Metastatic malignancy and infections are common causes of exudates


9.3 How do mesothelial cells and macrophages differ in their morphology?

Mesothelial cells

Usually isolated cells, Round cells, Dense staining cytoplasm, Round central nucleus, Stippled chromatin, Single nucleolus


Varied shape, Granular or vacuolated cytoplasm, Pale staining cytoplasm in MGG stain, Nuclei often bean-shaped


9.4 What typical cytological features are seen in rheumatoid effusions?

  • Multinucleated macrophages
  • Elongated macrophages
  • Granular debris
  • Cholesterol crystals


9.5 Small cell anaplastic carcinoma can rarely be confused with malignant lymphoma. Which immunocytochemical antibodies are helpful in resolving this differential diagnosis?

Small cell carcinoma can be stained with CD56, chromogranin, and synaptophysin. Cells of lymphoid origin can be marked with CD45.


9.6 List risk factors for malignant mesothelioma.

The main risk factor for mesothelioma is exposure to asbestos. Other minerals such as erionite, which have similar fibre structure to asbestos, can be linked to the development of mesothelioma. Simian virus 40 (SV40) is present in some human malignant mesotheliomas. Available evidence appears sufficient to link SV40 either alone or in conjunction with asbestos in causing malignant mesotheliomas.


9.7 Which antibodies are useful in helping to differentiate reactive mesothelial cells from malignant cells in serous effusions?

There is currently no absolute marker that can be used to differentiate between reactive mesothelial cells and malignant cells in serous effusions. Positive staining with epithelial membrane antigen (EMA) is used to support a diagnosis of malignancy. Desmin, an antibody to muscle tissue, can be used to differentiate between reactive mesothelial cells, mesothelioma, and adenocarcinoma. Desmin is generally expressed only in benign mesothelial cells; malignant mesothelioma and metastatic adenocarcinoma are unreactive and therefore do not stain.


9.8 What is the main role of peritoneal washing cytology?

Positive peritoneal washing cytology has been implemented in ovarian and peritoneal cancer guidelines because of its prognostic significance in ovarian tumours.  Positive peritoneal washings upstages the tumour. 

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