What is discoid atelectasis?

Discoid Atelectasis: Definition, Diagnosis, and Management

Discoid atelectasis is a form of pulmonary collapse characterized by a flat, plate-like or linear area of collapsed lung tissue that appears as a radiographic abnormality on chest imaging. It represents one of several types of atelectasis, which is defined as a state of collapsed and non-aerated lung parenchyma 1.

Types and Mechanisms

Discoid (also called platelike or linear) atelectasis is one of several morphological patterns of atelectasis, which can be categorized as:

• Segmental, lobar, or whole lung atelectasis
• Subsegmental atelectasis
• Platelike, linear, or discoid atelectasis
• Round atelectasis (also known as Blesovsky's syndrome, folded lung, or shrinking pleuritis)
• Generalized or diffuse atelectasis 2

The underlying mechanisms causing atelectasis include:

1. Resorption atelectasis - Caused by resorption of alveolar air distal to airway obstruction
2. Adhesive atelectasis - Results from surfactant deficiency
3. Passive atelectasis - Due to pneumothorax, diaphragmatic dysfunction, or hypoventilation
4. Compressive atelectasis - Caused by tension pneumothorax, space-occupying lesions, or abdominal distention
5. Cicatrization atelectasis - Results from pulmonary fibrosis
6. Gravity-dependent atelectasis - Due to gravity-dependent alterations in alveolar volume 2

Radiographic Appearance and Diagnosis

Discoid atelectasis appears as a thin, linear opacity on chest radiographs, often horizontally oriented and most commonly seen at the lung bases. The diagnosis of atelectasis is based on direct and indirect radiographic signs:

• Direct signs: Crowded pulmonary vessels, crowded air bronchograms, and displacement of interlobar fissures
• Indirect signs: Pulmonary opacification, elevation of the diaphragm, shift of mediastinal structures, displacement of the hilus, compensatory hyperexpansion of surrounding lung, approximation of ribs, and shifting granulomas 2

CT imaging is more sensitive than conventional chest X-rays for detecting atelectasis and is recommended when the diagnosis is uncertain or to better characterize the extent and cause 3.

Clinical Significance

Discoid atelectasis is often a transient finding that may be asymptomatic or associated with mild respiratory symptoms. It is commonly seen in:

• Post-operative patients, especially after abdominal or thoracic surgery
• Patients on bed rest
• Patients with shallow breathing due to pain or sedation
• Patients with pleural effusions or other pleural abnormalities

Unlike round atelectasis (which may mimic a tumor), discoid atelectasis rarely presents a diagnostic challenge in distinguishing it from malignancy 4.

Management

Management of discoid atelectasis depends on the underlying cause and severity:

1. Preventive measures:

   • Early mobilization
   • Deep breathing exercises
   • Incentive spirometry
   • Adequate pain control to allow for effective coughing and deep breathing

2. Treatment approaches:

   • Chest physiotherapy and postural drainage
   • Bronchodilator therapy when bronchospasm is present
   • Anti-inflammatory therapy if inflammation is contributing
   • Removal of persistent mucous plugs by bronchoscopy in severe cases 1

3. For mechanically ventilated patients:

   • Application of positive end-expiratory pressure (PEEP)
   • Periodic recruitment maneuvers
   • Avoiding high FiO2 (>0.4) when possible to prevent atelectasis formation 3, 5

Monitoring and Follow-up

• Repeat chest imaging to confirm resolution
• Monitor respiratory status, including oxygen saturation
• Assess for complications such as pneumonia or respiratory failure
• Continue preventive measures in high-risk patients 3

Distinguishing Features from Other Forms of Atelectasis

Unlike round atelectasis (which presents as a mass-like lesion and may be mistaken for a tumor), discoid atelectasis has a characteristic linear or plate-like appearance. Round atelectasis is often associated with asbestos exposure and is characterized by the "comet sign" (a band connecting the mass to an area of thickened pleura) 4, 6.

Discoid atelectasis also differs from lobar atelectasis, which involves collapse of an entire lobe and produces more significant volume loss and radiographic changes 2, 7.