Thoracic Imaging 2003 - Society of Thoracic Radiology

Unusual Manifestations of Lung Cancer
Michelle S. Ginsberg, M.D.
Objective
The common cell types of lung cancer have certain typical
radiographic appearances which will be briefly discussed.
However it is important to be familiar with the more unusual
presentations as well. The purpose of this review is to suggest
the correct diagnosis of bronchogenic carcinoma when the radiographic
manifestations of a particular tumor are rare, mimic
benign disease, or suggest disease of organs other than the lung.
The appearance of missed lung cancer, and means of improving
detection of these lesion will also be discussed.
Adenocarcinoma
Adenocarcinoma is the most common cell type of bronchogenic
carcinoma and accounts for approximately 50% of
cases. CT usually demonstrates a solitary peripheral pulmonary
nodule. The nodule may be smooth or spiculated. Hilar and
mediastinal lymph node involvement and distant metastases are
frequently present at the time of diagnosis. Peripheral tumors
may directly invade the pleura and grow circumferentially
around the lung and mimic diffuse malignant mesothelioma. 1
Central tumors may directly invade mediastinal structures or via
the pulmonary veins invade the left atrium.
Bronchioloalveolar carcinoma
Bronchioloalveolar carcinoma is considered a subtype of
adenocarcinoma and commonly presents as a solitary nodule. 2
There may also be surrounding ground glass opacity. Cavitation
an infrequent finding in adenocarcinoma may be seen in bronchioloalveolar
carcinoma. 3 Although less common, consolidation
and multiple small pulmonary nodules are other forms of
presentations. 3 High-resolution CT may demonstrate air attenuation
and pseudocavitation within the nodules corresponding to
small bronchi and cystic spaces. 4 Unusual radiographic appearances
include lobar atelectasis, expansile consolidation without
air bronchograms, or elongated lobulated opacity resembling
mucoid impaction. 5,6
Squamous cell carcinoma
Squamous cell carcinoma most often presents as a central
endobronchial obstructing lesion with associated atelectasis or
post obstructive pneumonia. Less commonly approximately a
third of these tumors may present as a solitary peripheral nodule
with or without cavitation. 7 When the tumor cavitates, the inner
wall is typically thick and irregular, and if secondarily infected
may develop an air fluid level.
Undifferentiated large cell carcinoma
Undifferentiated large cell carcinoma usually presents as a
large peripheral lesion, although a smaller proportion may also
be centrally located. These tumors grow rapidly and metastasize
early often presenting with hilar or mediastinal adnopathy.
Giant-cell carcinoma is a subtype with multiple giant cells and a
more aggressive behavior and poorer prognosis.
Multiple primary carcinomas
Synchronous lesions are defined as the presence of two
tumors at the time of or closely following initial diagnosis. The
incidence of synchronous multiple primary tumors is less than
3.5% of all lung cancer patients. 9 This number may even be
higher depending on the cell type and how carefully further primary
tumors are sought as well as the rigidity of the criteria
used to define the tumors as primary lesions. Difference in cell
type is an accepted criteria, however tumors of the same histologic
type must be physically quite separate as well as separated
by noncancerous lung tissue. 9,10
Metachronous lesions are defined as the second cancer
appearing after a time interval, usually 12 months or more.
These lesions compromise at least two thirds of multiple pulmonary
neoplasms, and on average are recognized 4 to 5 years
after the first primary. 10%-32% of patients surviving resection
for lung cancer may develop a second primary tumor. 9 These
lesions are regarded as multiple primary lesions only if they
show unique histologic features. Squamous cell cancer is the
most common histologic type of multiple carcinomas.
Metastases
The adrenal glands are one of the most common sites of
metastases from lung cancer ranging from 5-10% of the time at
presentation. In our experience we have also seen two cases of a
mass within the adrenal gland that represented a collision tumor
consistent of contiguous adrenal adenoma and metastasis.
Lung cancer may present with unusual sites of metastases.
For example the gallbladder an unusual site of metastatic disease
in general can be the site of a lung metastasis.
The kidneys, pancreas and small bowel may also be sites of
metastases and may be radiographically indistinguishable from
a primary tumor of that organ. Serosal and mesenteric implants
may become quite large. Invasion with perforation of the adjacent
bowl may result in a large mass with air within it having an
appearance indistinguishable from an abscess.
Muscle and subcutaneous tissues are other infrequent sites of
metastases from bronchogenic cancer.
Missed lung cancer
A missed lung cancer is unusual by virtue of the fact that it
was not detected. In contrast, most usual ones are detected
when in "easy" areas of lungs on a chest radiograph or CT.
Potentially resectable NSCLC lesions missed at chest radiography
were characterized by predominantly peripheral (85%) and
upper lobe (72%) locations and by apical and posterior segmental/subsegmental
locations in an upper lobe (60%). The missed
cancers had a median diameter of 1.9 cm. Most of these missed
lesions (98%) were obscured by anatomic structures on the
chest radiograph, most often by bones (ribs and clavicle). Only
the lateral radiograph revealed the cancer retrospectively in 5%
of patients. 11
Although chest CT is more sensitive for the detection of lung
nodules than chest radiographs, the potential for missing small
lung cancers at CT exists. A recent study by Li et al. evaluated
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