Thoracic Imaging 2003 - Society of Thoracic Radiology

Lung Cancer Detection Failures (CXR & CT)
Phillip M. Boiselle, M.D.
Introduction and Objectives:
Approximately 1 decade ago, Lillington estimated that
150,000 new solitary pulmonary nodules were detected each
year in the United States. Considering advances in CT technology
and CT utilization in the past decade, it is likely that the
number of nodules detected has increased substantially since
that time.
Although it is difficult to arrive at an accurate estimate of the
number of nodules detected each year, it is even more challenging
to determine how many nodules are missed. For example,
in routine clinical practice, the generally accepted error rate for
missed early lung cancer on chest radiographs is 20 to 50%.
However, error rates as high as 90% have been reported.
The learning objectives of this lecture are:
• To review the causes of lung cancer detection failures on
chest radiographs & CT
• To describe methods that can help to reduce lung cancer
detection failures.
Factors Contributing to Missed Lung Cancer:
Factors contributing to missed lung cancer include technical
considerations of the study (e.g. exposure factors, motion, and
suboptimal inspiration), lesion characteristics (e.g. lesion size
and conspicuity), and observer error. The latter is considered
the most important factor. There are three major types of
observer error: 1) scanning error: occurs if a nodule is not fixated
during the 350 msec that a lesion is focused on the fovea;
2) recognition error: occurs if a lesion is adequately scanned
but not recognized; and 3) judgement error: occurs when a recognized
abnormality is incorrectly interpreted as normal or not
clinically significant. Another type of observer error is satisfaction
of search, which describes the situation that occurs when a
radiologist fails to detect a lung cancer due to distraction by an
unrelated radiographic finding.
Missed Lung Cancer on Chest Radiographs:
In 1992, Austin et al. evaluated 27 cases of potentially
resectable non small cell lung cancers that were missed on chest
radiographs. The mean size of missed lesions was 1.6 cm, and
nearly one-third of lesions were greater than 2 cm in size. These
authors concluded that the single most frequently identified
cause of missed lung cancer was failure to compare the current
chest radiograph with multiple older chest radiographs.
Austin and colleagues recently revisited this topic in order to
determine whether there were changes in the last decade in the
failure of detection of potentially resectable non small cell lung
cancers. Interestingly, the mean size (2.1 cm) of missed lesions
in the new study was slightly but significantly increased compared
to the prior study. Both studies showed a striking
predilection for missed lung cancer in the upper lobes, especially
the apical and posterior segments of the right upper lobe.
In order to reduce the risk of missing lung cancer on chest
radiographs, one should always try to interpret chest radiographs
in the context of comparison to older chest radiographs.
Additionally, search satisfaction should be avoided by resisting
the temptation to end a search once a radiographic finding has
been made. Additional important factors for reducing detection
failures include optimizing the technical aspects of the study
and using appropriate viewing conditions.
Recent technological advances in chest radiography, including
dual energy subtraction and temporal subtraction techniques,
should lead to further improvements in nodule detection. It is
likely that these techniques will play an increasing role in the
future, along with methods of computer-aided diagnosis.
Missed Lung Cancer on CT
In 1996, studies by White et al. and Gurney described the
features of missed lung cancer on CT in 23 patients. Gurney
reported that failure of detection was predominantly due to
observer error. Small lesion size was considered a major factor
in this study as all peripherally located missed lesions measured
less than 3 mm in diameter. White et al. reported that endobronchial
lesions were most often overlooked, accounting for
two-thirds of missed cases. Mean lesion size was greater than 1
cm. Search satisfaction and observer fatigue were also cited as
factors for detection failure in this study.
In recent years, low-dose spiral CT (LDCT) has been used as
a screening tool for lung cancer detection, primarily in research
settings. Kakinuma et al. recently reported 7 cases of lung cancer
that were initially missed at screening LDCT and subsequently
detected on repeat LDCT screening studies performed 6
to 18 months later. Missed nodules were retrospectively categorized
as either conspicuous (mean diameter=11 mm; n=3) or
inconspicuous (mean diameter=6 mm; n=4). In order to reduce
the number of false-negative cases, these authors emphasize the
importance of examining noncalcified nodules with thin-section
CT, even when adjacent lesions of prior tuberculosis exist. They
also caution that one should carefully inspect pulmonary vessels
in order to distinguish them from small pulmonary nodules.
Despite an initial "missed" diagnosis, 6 of 7 lesions were Stage I
neoplasms at the time of diagnosis.
The ELCAP investigators have reported an analysis of missed
lung nodules on screening LDCT that were subsequently identified
on follow-up diagnostic CT scans. Among the 163 patients who
underwent diagnostic CT imaging, 36 (22%) had additional nodules
which were not detected on LDCT. The majority (85%) of
missed nodules measured 5 mm in diameter or less and none were
greater than 10 mm in diameter. Thus, small size appears to be an
important factor related to missed nodules on LDCT. Interestingly,
a majority of missed nodules were located peripherally.
Li et al. recently described the characteristics of missed lung
cancer in a large low-dose screening trial. In this study, 32 (39%)
of 83 primary lung cancers detected in an annual screening program
were missed on 39 CT scans. Detection errors were responsible
in approximately 60% of cases and interpretation errors
were responsible in the remaining 40% of cases. Lesions missed
due to detection error were significantly smaller (9.8 mm versus
15.9 mm) than those missed due to interpretative error. Lesions
missed due to detection error were also more likely to be groundglass
in attenuation. With regard to interpretation error cases, the
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