Answers

Short answers

1. Posteroanterior and lateral chest radiographs show complete collapse of the left upper lobe.

2. In left upper lobe collapse, hyperinflation of the superior segment of the left lower lobe occurs. This aerated segment is lucent and shaped like a sickle; it outlines the aortic knob on the posteroanterior radiograph (indicated by the arrowhead in the left hand panel of the figure).¹

3. Bronchogenic carcinoma (either endobronchial or causing extrinsic compression), lymphadenopathy, mucous plugging (as a result of asthma, cystic fibrosis, patient being in intensive care), foreign body aspiration, iatrogenic causes (such as misplaced endotracheal tube), and rare tumours such as endobronchial carcinoid.

4. Bronchoscopy, computed tomography (thorax, liver, and adrenals), and positron emission tomography if needed.

Long answers
Radiological findings
The posteroanterior radiograph and lateral chest radiograph show complete collapse of the left upper lobe (fig 1). This is seen on the posteroanterior radiograph as a veil-like increased density projected over the left hemithorax with associated elevation of the left hemidiaphragm and loss of definition of the left side of the mediastinum (fig 1a; arrow).² On the lateral view the collapsed upper lobe is clearly demarcated from the lucent lower lobe by the oblique fissure (fig 1b; arrows). Figure 2 is a diagrammatic representation of this phenomenon. Classic chest radiographic appearances also occur for the other types of lobar collapse.³

View larger version (15K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 2 Diagram showing collapse of the left upper lobe of the lung, which collapses forwards. It thus presents no sharp margins on the frontal film (a), instead it casts a veil-like opacity over the left hemithorax, normally more dense towards the apex. Volume loss occurs in the left hemithorax, with elevation or tenting of the left hemidiaphragm (curved arrow). The aortic knuckle is visible (arrowhead), as is the descending thoracic aorta (arrow). The left heart border is also commonly obscured. On a lateral film (b) the collapsed lobe is visible as a band of soft tissue density retrosternally; its sharp posterior margin is produced by the almost vertical left oblique fissure. The left fissure moves anteriorly compared with the right, the arrow shows the distance between the right and left oblique fissures. The outline of the cardiac silhouette can still be seen

 
The luftsichel sign
The luftsichel sign is a clue to the diagnosis of left upper lobe collapse. As the left upper lobe collapses, it moves anteriorly and superiorly to lie against the anterior chest wall, with the hyperexpanded left lower lobe located behind the upper lobe.¹ The axial post-contrast computed tomography image of the thorax (fig 3) shows the aerated apical segment of the left lower lobe posteriorly adjacent to the aortic arch (AA), leading to the luftsichel sign. Computed tomography also shows complete collapse of the left upper lobe. Mediastinal lymph node enlargement can be seen (arrow). A soft tissue mass fills the left hilum, with irregularity of the left main pulmonary artery suggesting invasion (arrowhead).

View larger version (57K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 3 (a) Axial post contrast computed tomography of the thorax shows the aerated apical segment of left lower lobe (arrow) posteriorly adjacent to the aortic arch (AA), leading to the luftsichel sign. The image also demonstrates complete collapse of the left upper lobe. (b) Computed tomography at the same level as in part (a) but on lung windows. (c) Computed tomography showing mediastinal lymph node enlargement (arrow). A soft tissue mass fills the left hilum with irregularity of the left main pulmonary artery suggesting invasion (arrowhead). The descending thoracic aorta (A) is outlined laterally by the aerated apical segment of the left lower lobe

 
Underlying disease processes
Underlying disease processes include:

Luminal obstruction: caused by bronchogenic carcinoma; mucous plugging (as a result of asthma, cystic fibrosis, or patients being in intensive care); foreign body aspiration; misplaced endotracheal tube; clots; or less commonly endobronchial lesions such as carcinoid, metastases, and lymphoma.

Stenosis of the bronchus: caused by granulomas, inflammation, polychondritis, or radiotherapy.

Extrinsic compression: caused by bronchogenic carcinoma, lymphadenopathy, or rarely mediastinal tumours (such as sarcoma).⁴

Any lesion causing luminal obstruction or narrowing, either intrinsic or extrinsic, can cause lobar collapse.⁵ In postoperative patients, the most common cause is a mucous plug. The incidence of lobar collapse caused by a mucous plug in children and adults in intensive care has been reported to be as high as 15%.⁶ Outside intensive care, the relative frequency of the various causes of lobar collapse are not documented in the literature; however, in adults a central obstructing tumour or mediastinal lymph node enlargement secondary to spread of tumour should always be considered as the underlying cause. Bronchogenic carcinoma is relatively uncommon in adults under 40, and bronchial carcinoid tumour should be considered in such patients. The most common causes in children are an inhaled foreign body (particularly a peanut, which cannot be visualised by plain radiography) and mucous plugging in asthma.

Further investigations
In many patients with lobar collapse, the cause is apparent from the patient’s history, clinical findings, and chest radiograph—for example, mucous plugging in patients with asthma or those in intensive care. In a patient presenting with acute lobar collapse, vigorous coughing and chest physiotherapy are the first line treatment.⁷ If this does not reverse the findings, the possibility of mechanical obstruction should be considered. In these patients bronchoscopy can be both diagnostic (by detecting a bronchogenic carcinoma) and therapeutic (by clearing the mucous).⁷ In patients with a suspicion of malignancy, current evidence recommends initial computed tomography because this can improve the diagnostic yield from bronchoscopy by providing information about whether the tumour is likely to be accessible by bronchoscopy and to provide a "road map" for the bronchoscopist to access the lesion.⁸ As in this case, computed tomography should be performed of the thorax, liver, and adrenals, which are common sites of metastases. Computed tomography is highly sensitive for detecting primary bronchogenic cancer and mediastinal lymph node stage.⁹ It can also detect endobronchial lesions.⁴ In this case, squamous cell carcinoma was diagnosed by bronchoscopy and biopsy. The histological diagnoses of squamous cell carcinoma, adenocarcinoma, and large cell carcinoma are grouped together for treatment purposes as non-small cell lung carcinoma. If tissue diagnosis cannot be obtained by bronchoscopy, percutaneous computed tomography guided biopsy of a lung mass can be performed.

Overview of the staging of non-small cell lung cancer with imaging
A primary aim of imaging is to eliminate unnecessary thoracotomy in patients in whom resection is not possible. The addition of positron emission tomography to the staging of these patients has enhanced the accuracy of the initial work-up. It has enabled regional lymph node metastases and spread to be detected in patients with apparently localised disease. The revised International System for Staging Lung Cancer 1996, which is based on the TNM classification, is the standard staging classification currently used (figs 4 and 5).^{10 11}

View larger version (37K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 4 TNM classification of tumours

 

View larger version (24K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 5 Relation between TNM subset and stage. Staging is not relevant for occult carcinoma, designated TX N0 M0

 
Stage I and II tumours are suitable for surgical treatment. Stage IIIA disease includes patients with potentially resectable ipsilateral mediastinal metastases who may be suitable for surgery after neoadjuvant therapy and patients with "bulky" nodal disease who require non-surgical treatment only.¹² Chemoradiotherapy is the only recommended treatment for most patients with stage IIIB disease. Stage IV disease includes any patient with distant metastases and is treated with palliative chemoradiotherapy only.

The seventh edition of the TNM Classification of Malignant Tumors is due to be published early in 2009. In preparation for this, the International Association for the Study of Lung Cancer established its lung cancer staging project in 1998. This committee recommended changes to the staging of lung cancer which include adding extra cut-offs for tumour size, with tumours greater than 7 cm moving from T2 to T3; reassigning the category given to additional pulmonary nodules in some locations; and reclassifying pleural effusion as an M descriptor. In addition, it is suggested that T2b N0 M0 cases be moved from stage IB to stage IIA, T2a N1 M0 cases from stage IIB to stage IIA, and T4 N0-1 M0 cases from stage IIIB to stage IIIA. The proposed changes would improve the alignment of TNM stage with prognosis and, in certain subsets, with treatment.¹³

Computed tomography
Computed tomography should be carried out in all patients with non-small cell lung cancer to localise the primary tumour and to provide information about resectability. It can also identify mediastinal adenopathy, mediastinal invasion, pleural thickening or nodularity, and chest wall invasion. The intravenous contrast agent used for computed tomography is associated with a low risk of anaphylaxis (mild anaphylactic reactions occur in 0.7-3.1% and severe reactions in 0.02-0.04% of procedures) and can cause renal impairment in patients with background renal impairment.¹⁴ Computed tomography is avoided in pregnancy because of the radiation dose, although it can be performed on the thorax with shielding of the abdomen if absolutely necessary. If a short axis diameter greater than 10 mm is used as the criterion for nodal positive disease, computed tomography has a pooled sensitivity and specificity of 57% and 82%, respectively.⁹ Because of this relative insensitivity for mediastinal nodes, all patients with suspected N2 disease and T stage 3 or less on computed tomography should be further investigated with mediastinoscopy or positron emission tomography (or both) to detect lymph nodes metastases.^{15 16} Patients with obvious N3 disease on computed tomography are at least stage IIIB and, therefore, not eligible for resection, which eliminates the need for mediastinoscopy. Distant metastases are seen in 40-49% of patients at presentation, especially metastasis to the adrenals, bones, liver, or brain.

Positron emission tomography
Positron emission tomography or integrated positron emission tomography and computed tomography is becoming the investigation of choice for guiding preoperative mediastinal lymph node staging in patients with diagnosed non-small cell lung cancer. Current National Institute for Health and Clinical Excellence guidelines support the use of positron emission tomography in all patients who are suitable for surgery and who are negative for nodal disease on computed tomography.¹⁷ Like computed tomography, positron emission tomography exposes the patient to a high dose of radiation and is used mostly for evaluating malignancy. Adding positron emission tomography to the staging process altered the stage in 27-62% of patients with non-small cell lung cancer, and prevented unnecessary thoracotomy in 20% of patients.^{18 19} All positive nodes should be further evaluated by direct sampling at mediastinoscopy to ensure that surgery is not withheld from a potentially curable tumour.²⁰ Around 11-17% of patients otherwise suitable for surgery will have extrathoracic disease on subsequent whole body positron emission tomography.¹³

Cite this as: BMJ 2008;337:a1505