Derived from the Latin word segmentum, meaning “section” or “division,” and the Greek word atelectasis, meaning “incomplete expansion.” The term refers to the collapse of a discrete lung segment.
AKA
Segmental collapse
Definition
What is it?
Segmental atelectasis refers to the collapse of one or more anatomical segments of the lung, typically resulting from obstruction of a segmental bronchus or external compression of the lung segment.
Caused by
Obstruction of a segmental bronchus due to:
Mucus plugging (e.g., in asthma, cystic fibrosis, or post-surgery)
Foreign body aspiration
Endobronchial tumors
Bronchial inflammation or infection (e.g., bronchitis)
Compression of lung segments from:
Pleural effusion
Pneumothorax
Adjacent mass effect (e.g., lymphadenopathy or tumors)
Postoperative states due to hypoventilation or splinting
Resulting in
Alveolar collapse within the affected segment
Volume loss and displacement of adjacent lung structures
Impaired ventilation and gas exchange in the affected area
Structural Changes
Collapse of alveoli within a discrete anatomical segment
Displacement of fissures and adjacent structures toward the collapsed segment
Compensatory hyperinflation in neighboring lung areas
Pathophysiology
Segmental atelectasis develops when airflow to a lung segment is obstructed, leading to resorption of trapped air and alveolar collapse. Alternatively, external compression of a lung segment can directly force alveoli to collapse. The collapse results in volume loss, reduced gas exchange, and distortion of lung anatomy, often causing a localized shift of fissures and structures.
Pathology
Collapsed alveoli with possible mucus plugging in the airways
Minimal to moderate inflammation, depending on the underlying cause
Potential associated infection in cases of obstructive atelectasis
Radiology in Detail
CXR
Findings
Wedge-shaped or triangular opacity corresponding to a collapsed segment
Volume loss with crowding of pulmonary vessels and displacement of fissures
Air bronchograms if the segmental bronchus remains patent
Associated Findings
Compensatory hyperinflation in adjacent lung areas
Possible associated pleural effusion or mediastinal shift toward the affected segment
CT
Parts
Discrete lung segment, delineated by anatomical boundaries
Size
Corresponds to the size of the collapsed segment
Shape
Triangular or wedge-shaped opacity with the apex pointing toward the hilum
Position
Affected lung segment varies; commonly involves lower lobe segments due to gravity-dependent airflow
Character
Dense consolidation with possible air bronchograms
Sharp demarcation from adjacent aerated lung tissue
Time
Acute in cases of obstruction or compression (e.g., mucus plugging or pneumothorax)
Chronic in cases of fibrotic or cicatricial changes
Associated Findings
Bronchiectasis or infection in chronic cases
Ground-glass opacities or interstitial thickening if associated inflammation is present
Other Imaging Modalities
MRI/PET CT/NM/US/Angio
MRI: Limited role but may aid in assessing associated soft tissue abnormalities
PET-CT: Useful for evaluating metabolic activity in cases of suspected malignancy causing segmental collapse
Ultrasound: May detect pleural effusion or assess diaphragmatic motion in postoperative atelectasis
Key Points and Pearls
Segmental atelectasis is characterized by collapse of a discrete lung segment, often appearing as a wedge-shaped opacity on imaging.
Common causes include mucus plugging, foreign body aspiration, and compression from pleural effusion or masses.
Air bronchograms are a key imaging feature when the segmental bronchus remains patent.
CT is the preferred modality for detailed evaluation, delineating the segmental anatomy and identifying underlying causes.
Management involves addressing the underlying cause, such as bronchoscopy for mucus plugging or removal of a foreign body, and supportive measures like physiotherapy and incentive spirometry.
