A bleb in radiology refers to a small, thin-walled air-filled space located within or just under the visceral pleura of the lung. Blebs are typically less than 1-2 cm in diameter and are formed due to the rupture or dissection of alveoli into the subpleural space. They are benign but can predispose to complications like spontaneous pneumothorax if they rupture.

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Radiological Features

1. Chest X-Ray (CXR):
   • Often not visible due to their small size and thin walls.
   • Indirect signs, such as a pneumothorax, may suggest the presence of a ruptured bleb.
   • Occasionally seen as a small, peripheral air-filled lucency near the lung apex.
2. Computed Tomography (CT):
   • Appearance:
     • Thin-walled, round, or irregular air-filled space located just beneath the visceral pleura.
     • Typically subpleural and most commonly found in the apices of the upper lobes.
   • Size:
     • Generally less than 2 cm in diameter.
   • Associated Findings:
     • Adjacent emphysematous changes (e.g., bullae, paraseptal emphysema).
     • Pneumothorax if the bleb has ruptured.
3. Ultrasound:
   • Rarely used for bleb detection but may help identify pneumothorax caused by a ruptured bleb through the absence of lung sliding or presence of a “lung point.”

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Common Causes and Associations

Blebs can occur idiopathically or secondary to underlying lung conditions:

1. Idiopathic (Primary):
   • Often seen in young, tall, thin males with no underlying lung disease.
   • Common cause of primary spontaneous pneumothorax.
2. Secondary to Lung Pathology:
   • Paraseptal Emphysema:
     • Destruction of alveolar walls near the pleura predisposes to bleb formation.
   • Chronic Obstructive Pulmonary Disease (COPD):
     • Increased intrapulmonary pressures can lead to bleb formation.
   • Cystic Lung Diseases:
     • Rare conditions like lymphangioleiomyomatosis (LAM) or Birt-Hogg-Dubé syndrome may present with blebs.
3. Trauma or Mechanical Ventilation:
   • Barotrauma can lead to the formation or rupture of blebs.

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Differential Diagnosis

1. Bullae:
   • Larger than blebs (>2 cm), with thicker walls, and located deeper within the lung parenchyma.
2. Cysts:
   • Well-defined, air-filled spaces with thicker walls and typically associated with specific lung diseases (e.g., LAM, histiocytosis X).
3. Cavities:
   • Air-filled spaces with thick, irregular walls due to infection, malignancy, or necrosis.
4. Pneumatocele:
   • Air-filled spaces with thin walls caused by acute lung injury or infection.

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Complications

1. Spontaneous Pneumothorax:
   • A ruptured bleb allows air to escape into the pleural space, leading to lung collapse.
2. Recurrent Pneumothorax:
   • Patients with multiple or persistent blebs are at risk of recurrence.
3. Tension Pneumothorax:
   • Rare but life-threatening if rupture results in air trapping under pressure.

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Management

1. Observation:
   • Small, asymptomatic blebs often require no intervention.
2. Pneumothorax Treatment:
   • Chest tube placement or needle decompression for large or tension pneumothorax.
3. Surgical Options:
   • Video-Assisted Thoracoscopic Surgery (VATS):
     • Used to remove blebs and perform pleurodesis in recurrent cases.
   • Pleurodesis (chemical or mechanical) to prevent recurrence.

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Clinical Relevance

Identifying blebs on imaging is critical for managing conditions like spontaneous pneumothorax and differentiating blebs from other cystic or air-filled lesions of the lung. CT is the gold standard for detecting and characterizing blebs due to its superior resolution.

 

 

Links and References

Fleischner Society

Anatomy.—A bleb is a small gas-containing space within the visceral pleura or in the subpleural lung, not larger than 1 cm in diameter (^,25).

CT scans.—A bleb appears as a thin-walled cystic air space contiguous with the pleura. Because the arbitrary (size) distinction between a bleb and bulla is of little clinical importance, the use of this term by radiologists is discouraged.