PITFALLS IN PULMONARY CYTOLOGY

Pulmonary cytology has sensitivity and specificity ranging
from 60% to 90%. 73 Even among the experienced cytopathologists,
there are equivocal cases that are diagnostic dilemmas.
74 Majority of the medicolegal pathology cases involve
surgical pathology, but approximately one third comprise
cytology specimens, with false-positive diagnoses on sputum
cytology/bronchial washing and lung aspirates being the third
leading source of errors. 75 False-positive diagnoses tend to be
more common than false-negative diagnoses. 74,76,77 Although
difficult to entirely avoid in an active, high-volume pulmonary
cytology practice, knowledge of complete clinical history (e.g.,
presence of localized mass lesion versus rapid clinical course/
acute pulmonary damage), radiological findings, and common
origins of cytological misinterpretations can minimize errors.
False-Negative Diagnosis Sputum, bronchoalveolar
lavage, and transthoracic fine-needle aspiration cytology specimens
are often used to diagnose pulmonary lesions. Sputum
and bronchoalvoleolar lavage specimens may not be accessible
to small peripheral lesions, so CT-guided transthoracic fineneedle
aspirations are employed to target the specific pathological
process. Despite image-guidance, false-negative diagnoses
in pulmonary fine-needle aspirations occur and are frequently
a consequence of inadequate sampling, 76,77 for which repeat
aspiration is recommended. 77 The negative predictive values of
fine-needle aspirations range from 53.3% 77 to 77%. 76
In some instances, false-negative diagnoses result from interpretive
errors, especially in squamous cell carcinomas associated
with marked active inflammation. A carcinomatous abscess
with few dysplastic, foreign body reaction to keratin 9 and malignant
cells in a predominantly inflammatory could be dismissed
as reactive epithelial changes. 78 Malignant characteristics
include keratinous fragments and/or ghost cells, irregular cells,
and pyknotic nuclei. 9 Metastatic breast carcinoma can appear
bland and be misclassified as a benign process. 74
False-Positive Diagnosis Since the implementation of
lung screening and CT scans, greater numbers of pulmonary
lesions are detected. In some instances, sophisticated imaging
modalities such as positron emission tomography (PET) are
used. PET positivity results indicate malignant/“active” lesions,
but sometimes, inflammatory processes also yield false-positive
results (Figs. 18.8 and 18.9).
Similarly, in cytology, several benign processes can mimic
carcinoma. Devoid of architectural clues evident in histological
sections, the distinction between reactive change/atypia
and malignant processes in cytology can be difficult. Some
lesions have been reported more often in exfoliative specimens
and others in fine-needle aspirations. Also, the various
entities usually emulate squamous cell carcinoma and/or
adenocarcinoma.
There are several sources of pulmonary cytological pitfalls
including infectious/granulomatous disease (fungal infections,
dirofilariasis, tuberculosis, Pneumocystis carinii , cytomegalovirus),
acute lung injury (diffuse alveolar damage [DAD],
thromboemboli, infarction), iatrogenic effect (chemotherapy,
radiotherapy), meosthelial cell proliferation, benign neoplasms
(e.g., hamartoma), prior procedure-related changes, and vegetable
contaminants. 79
Infections
Fungal Granulomas in the lung are associated with various
etiologies, including infectious processes. Fungal infections
(e.g., Aspergillus ) are a source of reactive squamous atypia
that mimics keratinizing squamous cell carcinoma. 18,80,81 The
cytological specimens from the infections show squamous
cells arranged singly and in clusters 18 with eosinophilic to orangeophilic
cytoplasm, hyperchromatic nuclei, high nuclear:
cytoplasmic ratio, and smudgy chromatin. In contrast, squamous
cell carcinomas have more orangeophilic cytoplasm and
greater numbers of single atypical cells. 18 Necrosis may be associated
with both lesions 18 and cannot, therefore, be useful in
discriminating between the two.
Mycobacterial Similarly, mycobacterial infections (i.e.,
tuberculosis) produce granulomatous inflammation, which
can simulate carcinoma. 78 However, coexistence of tuberculosis
and lung carcinoma including squamous cell carcinoma
(the predominant subtype 82 ), adenocarcinoma, large cell carcinoma,
and small cell carcinoma has also been described. 83
Parasitic (Dirofilariasis) Dirofilaria immitis is a canine
heart roundworm that can infect humans. Pulmonary disease
may be incidental or symptomatic, present as solitary or multiple
nodule(s), 84 and suggest malignancy radiographically
and clinically. 85 The infection can cause infarction secondary
to pulmonary artery embolization of the parasite from
the right ventricle and granulomatous reaction surrounding
a thrombosed artery. 84 Some cytological cases are associated
with reactive squamous metaplasia of surrounding airways,
which may be erroneously diagnosed as squamous cell carcinoma,
84 whereas others demonstrate papillary clusters with
cells containing high nuclear:cytoplasmic ratio, nuclear irregularity,
mild hyperchromasia, and prominent nucleoli in
the perilesional bronchiolar epithelium suggestive of adenocarcinoma.
Scarcity of atypical cells and lack of significant
hyperchromasia should favor a reparative/reactive process in
pulmonary dirofilariasis. 86,87 This distinction is important
because dirofilarial infection is benign and requires no surgical
intervention. 85
Pneumocystis Pneumoniae and Cytomegalovirus
False-positive diagnoses have been linked with cytomegalovirus
88 and P. pneumoniae 89 as well.
Wegener Granulomatosis Wegener granulomatosis,
although not of infectious etiology, is a systemic vasculitis characterized
by a triad of upper respiratory, lower respiratory, and
renal involvement. Pulmonary Wegener granulomatosis has
different histological appearances with the characteristic pattern
demonstrating geographic necrosis, multinucleated giant cells,
and mixed inflammatory infiltrate. Similar to the infectious and
granulomatous entities, cytological atypia of Wegener granulomatosis
may be a potential source of false-positive diagnosis. 90
Hyperchromatic atypical squamous cells in a background of
necrosis, acute inflammation, and hemorrhage may be misdiagnosed
as squamous cell carcinoma 90,91 and atypical bronchial
cells as BAC. 92
Acute Lung Injury Reactive type II pneumocytes, progenitors
of type I pneumocytes in response to injury, are present
in specimens when they are hyperplastic, thereby posing
a potential diagnostic pitfall. 74,93,94 In bronchoalveolar lavage
specimens, reactive type II pneumocytes have been associated
with acute lung injury, 95 organizing pneumonia, 78 alveolar
hemorrhage, 89 ventilator-associated pneumonia, 89 hypersensitivity
pneumonitis, 89 eosinophilic pneumonia, 89 medicationinduced
injury, 89 DAD, and embolism/infarction. The cells
tend to be large with high nuclear:cytoplasmic ratios and vacuolated
cytoplasm 89 suggestive of adenocarcinoma.
Diffuse Alveolar Damage DAD has acute and organizing
stages during which alveolar hyperplasia develops.
Bronchoalveolar lavage specimens obtained from patients
with DAD demonstrate cellular specimens with single cells,
two-dimensional sheets, and three-dimensional cell clusters 96
that can occasionally form glandlike structures with scalloped
edges suggestive of adenocarcinoma. 93 The cells have nuclear
atypia, cytoplasmic hobnails characteristic of hyperplastic
cells, 1 prominent nucleolus, 96 hyperchromasia, slight
nuclear irregularities, high nuclear:cytoplasmic ratio, 93 and
infrequently, dense cytoplasm suggestive of squamous differentiation.
96 Many of these features overlap with malignancy,
but lack of uniformity among cell clusters, lack of markedly
increased nuclear:cytoplasmic ratio, scalloping of cell groups
with hobnails, and intercellular clearing “windows” support
type II pneumocyte hyperplasia over carcinoma. 93
Pulmonary Embolism/Infarction Pulmonary embolism
with or without infarction can cause cytological atypia
suggestive of adenocarcinoma. 97–100 Atypical cytological features
include three-dimensional cell clusters with cytoplasmic
vacuolization, enlarged nuclei with regular borders, and
prominent nucleoli. Unlike malignant neoplasms, the atypia
is focal and fleeting, often apparent 2 to 3 weeks postthromboembolism.
99 Single atypical cells often seen in conjunction
with malignant neoplasms are lacking. 98,99,101
Type II Pneumocytes versus Malignancy There
is definite overlap between reactive type II pneumocyte hyperplasia
and carcinoma, particularly BAC. Several criteria
have been outlined in the literature to distinguish the lesions.
First and foremost, a search for cilia and/or terminal
bars is an important and simple clue to make a diagnosis
oriented to a benign process. Reactive/reparative processes
tend to have two-dimensional sheets, maintain uniformity
and polarity, 79 and demonstrate cellular streaming. 102 Two
cell populations 102 (i.e., relatively uniform and loosely cohesive
benign cells and dyscohesive malignant cells with
large nuclei), tissue fragments consisting of 2 cells with
common inner or outer community borders and single cells,
elongated or tenacious cytoplasmic borders, intranuclear intracytoplasmic
inclusions, paucity of multinucleated giant
cells, and increased nuclear area are more frequent in adenocarcinoma.
103 Other characteristics such as hyperchromasia,
prominent nucleoli, nuclear membrane irregularities,
elevated nucleus:cytoplasmic ratio, 103 and mitotic activity, 79
although often associated with malignancy, are also evident
in reactive processes. 103
Asthma Bronchial asthma results in excessive columnar
epithelial cell shedding, sometimes as papillary formations
suggestive of adenocarcinoma. 104 The cells tend to be of uniform
shape and size with peripheral palisading. 104 Presence of
eosinophils and Charcot-Leyden crystals is also helpful, but
lacking in the acute phase. 104
Lipoid Pneumonia Cytoplasmic vacuolization in lipid
pneumonia may also resemble vacuoles of mucinous adenocarcinoma.
79 Lack of a mucinous background and histochemical/
immunostains (mucicarmine, cytokeratin, CD68) can be
helpful in making the distinction.
Chemotherapy and Radiotherapy Many anticancer
drugs can cause atypical changes in the respiratory tract that
resemble adenocarcinoma and squamous cell carcinoma. 102
Cellular changes associated with chemotherapy and/or radiation
include cytomegaly with preserved nuclear:cytoplasmic ratio,
multinucleation, macronucleoli, and nuclear pleomorphism. 105
The chromatin is uniform or smudgy, but a coarse chromatin
pattern can be present. 102 Abnormal-appearing cells are often
part of a tightly cohesive cluster or sheet without prominent
single atypical cells (Fig. 18.9).
Mesothelial Cell Proliferations In transthoracic aspirates,
particularly of pleural-based lesions, mesothelium is
sometimes inadvertently sampled. Sheets of mesothelial cells
can be misdiagnosed as squamous cell carcinoma, 80 or the
honeycomb arrangement of relatively bland cells may suggest
a diagnosis of BAC. Recognition of intercellular windows in
mesothelial cells and, if necessary, immunohistochemical stains
for mesothelial cells (calretinin, cytokeratin 5/6, WT-1) and
epithelial cells (B72.3, BerEP4, CEA) are also helpful.
Pulmonary Hamartomas Pulmonary hamartomas may
also be mistaken for adenocarcinoma. 74,41 The myxoid background
may be interpreted as mucin, whereas bronchiolar hyperplasia,
intranuclear inclusions, intranuclear invaginations,
and multinucleation can suggest adenoarcinoma. 41,106,74
Unlike mucin, fibromyxoid stroma has fibrillar edges
and spindle-shaped nuclei. A cell block can also be made at
time of on-site evaluation for further characterization. The
mucicarmine stain would be negative, and S-100 immunostain
would highlight the spindle stromal cells. In addition,
when present, the chondroid/cartilaginous component may
be better preserved in cell block sections but not easily visualized
in smears.
Suture Granuloma and Posttracheostomy Atypia
Fine-needle aspirate of a PET-active lesion in a patient with
a history of multiple primary carcinomas was interpreted as
non–small cell carcinoma based on presence of dysplastic
cells. Surgical excision showed an inflammatory nodule at the
prior suture site. 107 Posttracheostomy atypia following laryngectomy
and/or tracheostomy can show cells with irregular
nuclear contours and fine or coarse chromatin suggestive
of squamous cell carcinoma. 108 Absence of a mass clinically
should dictate caution.
Vegetable Contaminant Patients with aspiration pneumonia
may have vegetable cells contaminants suggestive of
pulmonary epithelial cell atypia. 109 Features suggestive of malignancy
include linear arrangement of asparagus cells suggestive
of metastatic lobular breast carcinoma, 109 vacuolated and
swollen cytoplasm indicative of mucin, 109 and dark cytoplasm
reminiscent of atypical enlarged nuclei. 109 Regular quadrangular
shape, extremely large size and refractory walls favor vegetable
cell contamination. 109
Megakaryocytes Megakaryocytes are seen incidentally in
histological specimens as large, hyperchromatic, irregular cells
bulging from capillaries in patients with smoking history, sepsis,
cardiovascular disease, and metastatic malignancy. 110 Although
rare in cytology, their atypical appearance can mislead to a diagnosis
of malignancy. 11 Lobulated nuclei (single or multiple),
ruffled border, and variation in cytoplasm (dense centrally and
pale peripherally) are clues to megakaryocytic origin.
A cytological diagnosis is a synthesis of clinical, radiological,
and morphological features with appropriate sampling and
specimen preservation. False-positive diagnoses, particularly in
sputa, are of 10 related to insufficient clinical history. 73 Adjunct
studies such as immunohistochemical stains and fluorescence
in situ hybridization (FISH) analysis 74 may be helpful in some
cases. Despite these measures, cytology has limitations, and
a definitive diagnosis cannot always be ascertained. If uncertainty
remains, it is prudent to suggest additional sampling or
a frozen section prior to definitive surgery.