Linear Atelectasis around the Hilum on Chest Radiography: A Novel Sign of Early Lung Cancer

INTRODUCTION

Linear atelectasis is a focal area of subsegmental atelectasis with a linear shape. It is normally horizontal and sometimes oblique or perpendicular. Linear atelectasis may occur as a consequence of obstruction in the bronchus of a pulmonary subsegment. The collapsed lung tissue could be flattened, and it may be seen as a relatively thick, well-demarcated, linear opacity.[1]

To the best of our knowledge, linear atelectasis, especially located in the lower lung parenchyma, has usually been observed in simple hypoventilatory changes (i.e., the lung folding in on itself) in addition to some benign conditions such as pulmonary embolism or pneumonia or following aspiration.[2] Nevertheless, the linear focal atelectatic changes in perihilar lung parenchyma have not been reported to be associated with primary lung cancer.

In this study, we propose to describe an early roentgen finding of obstructing tumors, namely thick perihilar linear atelectasis, and ascertain whether this phenomenon could be used as a sign to detect radiographically occult primary lung cancer.

MATERIALS AND METHODS

Quantitative analysis

The diameter of each linear atelectasis was calculated as the diameter greatest in dimension, mostly acquired on the craniocaudal plane of PA radiographs and its distance from the cardiac border was determined as a minimum 1 cm to not include any hilar vascular structures or lymph nodes [Figure 1].

Close

Figure 1

Diameter of perihilar linear atelectasis acquired on craniocaudal plane on posteroanterior radiograph.

Export to PPT

The distribution of the perihilar linear atelectases was localized as follows: perihilum near the superior vena cava (SVC), perihilum near the right atrium and left-sided perihilum [Figure 2].

Close

Figure 2

The distribution of perihilar linear atelectasis was categorized as perihilum near superior vena cava, perihilum near right atrium and left-sided perihilum.

Export to PPT

RESULTS

Perihilar linear atelectasis was observed in 58 (0.012%) patients. Atelectasis was caused by an obstructing tumor in 21 (36%) patients [Figure 3] and a variety of other benign conditions in 37 (64%) patients [Figure 4 and Table 1].

Close

Figure 3

Left, (a) chest radiograph with left-sided perihilar linear atelectasis (asterisk) was caused by central bronchogenic carcinoma. Right, (b and c) computed tomography confirmed the linear atelectasis (asterisk) and also identified obstructing bronchogenic carcinoma.

Export to PPT

Close

Figure 4

(a-d) Posteroanterior chest radiographs demonstrate perihilar linear atelectasis was caused by variety of benign conditions.

Export to PPT

Table 1 Clinical and demographic features of the patients with perihilar linear atelectasis caused by obstructing tumor (tumor group) and benign causes (nontumor group)

Age and sex in atelectasis with or without concurrent central primary lung cancer: The mean age was 60.14 ± 9.26 years (range, 45–79 years) in the group with tumor and 65.73 ± 12.65 years (range, 34–87 years) in the group without concurrent tumor. There was no significant difference between the groups (P = 0.228). The group with tumor (female-to-male ratio: 4/17) and the group without tumor (female-to-male ratio: 22/15) were significantly different according to gender (P = 0.003) [Table 1].

Smoking history in patients with linear atelectasis: Fifteen out of 21 (71%) patients with primary lung cancers were smoked cigarettes, at a mean of 1.2 packs per day for 15 years (mean: 15.2 years; SD: ±4 years), and 21 out of 37 (57%) patients without tumors smoked cigarettes, at a mean of 1.1 packs per day for 13 years (mean: 13.3; SD: ±3.5 years). There was no significant difference between the groups (P = 0.315) [Table 1].

Three patients with linear atelectasis were found to have chest pain, four patients had shortness of breath, two patients presented with chronic cough, and one patient presented with hemoptysis as a symptom when the chest roentgenograms were acquired. There was no significant difference between the groups with or without lung cancer for the initial symptoms when the chest roentgenograms were acquired (P = 0.171) [Table 1].

None of the patients with linear atelectasis had associated ancillary findings of lung cancer on chest radiographs including narrowing or cutoff of the bronchus, pleural effusion, nodule, bronchiectasis, and evidence of mediastinal lymphadenopathy.

Craniocaudal dimensions of the atelectasis

The mean diameter of linear atelectasis was 6.95 (range: 2.5, 13.6) (SD: ±2.69) mm in the tumor group and 4.12 (range: 1.7, 7.8) (SD: ± 1.23) mm in the nontumor group. There was a statistically significant difference in diameter between the groups (P < 0.001) [Figure 5].

Close

Figure 5

Thickness of perihilar linear atelectasis was compared between the atelectasis caused by bronchogenic carcinoma or benign conditions.

Export to PPT

DISCUSSION

Primary lung cancers tend to originate from the bronchial walls and sometimes constitute a bronchial obstruction and may manifest radiographically as an atelectasis.[3] In the alveoli distal to the obstruction, the air could be trapped, leading to the appearance of obstructive atelectasis. Atelectatic changes in the tributary lung distal to the bronchial obstruction are relatively common abnormal radiographic findings in adults with obstructing tumors.

As atelectasis occurs following bronchial or bronchiolar obstruction, normal lung tissue with elastic features immediately above and below the atelectasis becomes emphysematous and permits collapse to occur in a horizontal direction. These focal linear atelectatic changes are usually found in the lower third of the lung fields, either unilaterally or bilaterally.[45] Most frequently, it is seen immediately above the diaphragm and always secondary to some other lesion, either intrathoracic or intra-abdominal.[67] Nevertheless, even after a decade, many radiologists and clinicians fail to utilize this important diagnostic finding of obstructing primary lung cancer to the best advantage. The focal atelectatic changes distal to the obstruction may be seen when some of the smaller pulmonary bronchi are occluded. The resulting areas of focal changes, such as linear atelectasis, may be suggestive of a diagnosis of occult lung cancers on the chest roentgenograms.

The diagnosis of central lung tumors is often difficult to establish on chest roentgenogram, especially when the tumor is small and obscured by the hilar structures.[8] The detection of radiographically occult lung cancer was made possible by the appearance of various radiologic findings.[9] Narrowing of the affected bronchi or focal bulging of the fissure bordering the collapsed lobe have been described in the literature[10] and could be identified rarely in chest radiographs of obstructive atelectasis. Identifying such roentgen findings, including signs of perihilar linear atelectasis, could be viewed as synonymous with taking the opportunity to make an early diagnosis of primary lung cancer. Nearly two-thirds of patients with primary lung cancer, which was difficult to detect by chest radiograph, were found to have early lung cancer. Because the survival rates of early bronchogenic cancers following resection are much higher than those of advanced stage, the effect of the recognition and detection of these roentgen findings are indeed substantial.[1112]

The propensity for bronchogenic cancer to cause atelectasis by occluding central bronchi has been studied previously. Byrd et al.[13] reviewed the initial chest radiographs of 114 patients with bronchogenic lung cancer, finding 76% of these patients had a hilar mass and 30% had signs of bronchial obstruction such as volume loss, consolidation, or obstructive pneumonitis. Chute et al.[14] found that 79% of 326 patients with small cell lung cancer presented with hilar or mediastinal involvement and that 35% had some degree of atelectasis.

Chest radiography may be an excellent diagnostic tool for showing segmental or lobar atelectasis and can be used to document central tumors as the cause of atelectasis on the basis of two major findings: evidence of a central hilar mass and evidence of perihilar thick linear atelectasis. Using both findings as plain film signs, the chest radiograph may identify atelectasis with a low false-positive rate. However, the chest radiograph is generally less sensitive than CT, indicating that in some cases, the chest radiograph cannot be used to determine if a central tumor is the cause of atelectasis.[15]

CT is able to diagnose obstructing tumors as a cause of atelectasis with an acceptable false-positive rate. In patients with postoperative acute atelectasis, clinically documented pneumonia or obstructive gross tumors on chest roentgenograms, the cause of atelectasis usually does not represent the diagnostic difficulty.[16] However, the demonstration of the pathologic cause of obstructive atelectasis in the absence of these findings may be a problem. Recent studies demonstrated that the bronchial patency and absence of a centrally located mass lesion on CT are reliable imaging findings that can be used to exclude primary lung cancers as a cause of atelectasis.[1718]

In general, the detection of hilar cancer is difficult due to the presence of variations in the anatomy of the hilar region.[19] In a screening program, Muhm et al.[20] found that 65% of lung cancers arising in the hilum were missed. In our study, lesions were skipped once in the chest roentgenogram of three patients. In one of these patients, the lesion showed little progress over a few years. The radiologist interpreted the lesions as benign linear atelectasis and did not express any suspicion of a possible tumoral lesion.

We retrospectively estimate that this 28% miss rate, which is detected in patients having perihilar linear atelectasis on chest radiograph, can be improved with the contribution of our results to the literature. The detection of early stage lung cancers may have a major impact on prognosis. Therefore, we think that chest radiographs with perihilar linear atelectasis need to be further evaluated by CT or bronchoscopy in high-risk groups.

We believe our study has some advantages. Our method of measuring linear atelectasis with quantitative assessment seems to be more objective and easy to interpolate in daily radiology practice.

Our study was retrospective, and as a result, there were some inherent limitations. The retrospective nature of the study hindered us from accurately registering the number of linear atelectasis on chest radiographs, and thus, the exact analysis of the accuracy of perihilar linear atelectasis could not have been determined. A plan to conduct a prospective study is needed to answer the following important questions: What is the prevalence of perihilar linear atelectasis? What are the sensitivity and specificity of screening using perihilar linear atelectasis?

CONCLUSION

To the best of our knowledge, no studies have been reported to address the association of perihilar linear atelectasis on chest radiography with the detection of early-form centrally located lung cancer in clinical practice. Thick perihilar linear atelectasis is a new diagnostic roentgen sign that could be suggestive of a diagnosis of primary lung cancer.