Approach to diagnostic cytopathology of serous effusions

Chapter 3 Approach to diagnostic cytopathology of serous effusions

Vinod B. Shidham, Barbara F. Atkinson

TABLE OF CONTENTS

GENERAL APPROACH 31

PROCESSING APPROACH 32

INTERPRETATION APPROACH 34

CYTOLOGIC APPROACH 36

Cell groups and intercellular cohesion 36

Arrangement of neoplastic cells 38

Cytoplasm of neoplastic cells 38

Special structures and cytologic features 38

Other features 40

IMMUNOCYTOCHEMICAL APPROACH 41

GENERAL APPROACH

Aspiration of an effusion is a relatively simple procedure. Cancer is one of the frequent causes of an effusion fluids and it may be the first manifestation of advanced cancer. Consequently, any general pathology laboratory may receive effusion for cytologic evaluation. As a consequence, all general pathologists and cytopathologists should be conversant with the diagnostic challenges and pitfalls of effusion fluid cytology. These facts emphasize the significance of understanding the approach to effusion fluid cytology by all practicing pathologists.

Finding neoplastic cells in effusion specimens not only reveals that a patient has cancer but also denotes the advanced nature of the disease, which, at this stage, is almost always incurable. Other than the detection of cancer cells in cerebrospinal fluid, no other exfoliative cytology specimen carries such an ominous prognostic significance to the detection of cancer cells. Apart from the finding of cancer cells, cytopathologic examination of serous effusions may reveal inflammatory conditions, parasitic infestations, bacterial, fungal, or viral infections, and certain other non-neoplastic conditions (see Chapter 6).

Other than high-grade neoplasms with pleomorphic cells (Figures 3.11, 3.12), the standard cytologic criteria of malignancy based on evaluation of single cell morphology are not applicable for most of the effusion cytology specimens. Since cells in a fluid medium ‘round up’ because of surface tension, the native shapes of cancer cells cannot be a guiding feature for deciding the primary origin of malignant cells. As effusion fluids are nutrient rich, the cancer cells with the potential to proliferate may continue to divide and form proliferation spheres. It is crucial to consider these factors when interpreting effusion cytology.

Figure 3.11 Metastatic poorly differentiated non-small-cell carcinoma of lung (pleural fluid). The specimen predominantly shows non-cohesive solitary cells (a–d). The neoplastic cells (NC inset d) are pleomorphic, with unequivocal features of malignancy. Mitotic figures (MF in c) are present in concert with apoptotic cells, which show apoptotic bodies (AP in d). Solitary cells (NC in d) may resemble high-grade lymphoma cells. DQ-stained preparation and immunocytochemistry on cell block sections may help in cases with unknown primary. This patient had poorly differentiated adenocarcinoma of lung. AP, apoptotic cells; MF, mitotic figure; NC, neoplastic cells. [a–d, PAP-stained SurePath preparation (a, 10×; b, 40×; c,d, 100×; d inset, 100× zoomed).]

Figure 3.12 Metastatic poorly differentiated adenocarcinoma (peritoneal fluid). Specimen predominantly shows neoplastic cells (NC in insets c,d) with unequivocal features of malignancy. Mitotic figures (MF in c) are present in concert with apoptotic cells with apoptotic bodies (AP in d). Some cells show unequivocal cohesive pattern (arrowheads), consistent with carcinoma. Such specimens do not need ancillary help of DQ stain or cell block sections for immunocytochemistry, unless a search for unknown primary is indicated. AP, apoptotic cells; MF, mitotic figure; NC, neoplastic cells. [a–d, PAP-stained SurePath preparation (a, 10×; b, 40×; c,d, 100×; insets of c,d, 100× zoomed).]

Although adenocarcinomas are the most common neoplasm to spread to the peritoneum, pleura, and pericardium, almost any type of cancer may do so. Any neoplasm including carcinomas, melanomas, hematopoietic neoplasms, sarcomas, and mesotheliomas may involve serous cavities. Carcinomas are almost always adenocarcinomas. In general, sarcomas metastatic to serous cavities are rare. The morphologic features of most of the cancer cells in effusion smears are different from those seen in exfoliative, brushing, and fine-needle aspiration cytology.

Reactive mesothelial cells are a consistent component of effusion fluids, and they have significant morphologic overlap with malignant cells (see Table 2.2). Consequently, the interpreter must be aware of the wide range of cytomorphologic appearances of reactive mesothelial cells in effusion fluids (see Figures 2.1, 2.2, 2.6, 2.7; Chapters 1, 2).

Table 3.2 Clinical conditions associated with the pitfall of malignant misinterpretation

Effusion fluid	Clinical association
Peritoneal fluid	Cirrhosis Renal failure with uremia Pancreatitis Bile peritonitis Huge intra-abdominal benign masses: e.g. ovarian fibroma (with florid reactive mesothelial hyperplasia of the overlying serosal surface)³⁷
Pleural fluid	Pulmonary infarction ³⁸ Infection/inflammation Pancreatitis ³⁵
Pericardial fluid	Pericarditis—viral Congestive heart failure
All fluids	Collagen vascular diseases Chemotherapy ³⁶ Radiation therapy ³⁶

Figure 3.1 Algorithm for evaluation of a ‘second foreign population’.

Figure 3.2 Cytologic evaluation of effusion fluids for primary site.^c

Figure 3.6 Hematoxylin and eosin-stained sections of cell block of an effusion (metastatic colonic adenocarcinoma, pleural fluid).

Figure 3.7 Metastatic adenocarcinoma (pleural fluid). An example with morphologically identifiable unequivocal ‘second foreign population’ (red arrow NC) other than mesothelial cells (blue arrow RM) and inflammatory cells (brown arrow IC) in DQ- and PAP-stained smears. This ‘second population’ of cells (red arrow NC) is easier to identify with the DQ stain (a) than with the PAP stain (b). IC, inflammatory cells; RM, reactive mesothelial cells; NC, neoplastic cells. [a, Diff-Quik-stained Cytospin smear; b, PAP-stained ThinPrep smear (a,b, 100× zoomed).]

To avoid various diagnostic pitfalls and increase the diagnostic accuracy, it is essential to understand multifactorial nuances in the setting of effusion fluid cytology. If one is familiar with the cytomorphologic features and the pitfalls associated with the effusion cytology, diagnostic interpretation may be facilitated, even without having to resort to the ancillary studies (Figures 3.1, 3.2).

PROCESSING APPROACH

The backbone of effusion cytopathology is to organize the specimen processing in such a manner that it accomplishes the following objectives:

1. Detection of any ‘second population of foreign cells’ other than the mesothelial and inflammatory cells (Figure 3.7).

2. Studying the nuclear details of the ‘second population’.

3. Semiquantitative evaluation of individually scattered mesothelial cells and large groups of three-dimensional mesothelial cells, as in mesotheliomas (Figure 3.1(5)).

4. Objective confirmation of the ‘second foreign population’ and the differential diagnosis of their primary neoplasm.

Any approach that does not address these objectives may lead to misinterpretation and suboptimal results.

In our experience:

The 1st objective is best evaluated in Diff-Quik (DQ)-stained (Romanowsky-stained) air-dried Cytospin smears (or an air-dried direct smear prepared from the cell pellet).

The 2nd objective is best evaluated in Papanicolaou (PAP)-stained smears (such as wet fixed direct smears from the cell pellet, liquid-based cytology preps—SurePath, ThinPrep, Cytospin smears, or filters).

The 3rd objective is best evaluated in a DQ-stained direct smear prepared from the fluid prior to concentration.

The 4th objective is evaluated better if a cell block is prepared for ancillary tests, including immunostaining, as indicated.

Based on this approach, in our laboratory we routinely process (see Chapter 14, Table 14.2, Figure 14.1) all effusion fluids by preparing a DQ-stained direct smear of unconcentrated effusion specimen (Figure 3.3), DQ-stained Mega-funnel Cytospin smear from the concentrated cell pellet (Figure 3.4), and PAP-stained SurePath preparation (Figure 3.5). In addition, in some cases with differential diagnosis of malignancy, the remaining effusion fluid is processed for cell block preparation for hematoxylin and eosin (HE)-stained sections (Figure 3.6), and for elective immunocytochemistry (Figure 5.2).¹