A lung bleb is a small, air-filled sac that forms on the surface of the lung, typically located just beneath the visceral pleura (the thin membrane lining the lung). These blister-like pockets are generally considered a minor anatomical variation. Although often asymptomatic and harmless, these fragile structures hold the potential for a serious complication if they rupture.
Defining a Lung Bleb
A bleb is structurally defined as a small, gas-filled cystic structure situated just beneath the visceral pleura. These air pockets are usually very small, often having a diameter of less than one or two centimeters. The wall of a true bleb is extremely thin, often less than one millimeter, and can be imperceptible on imaging. Blebs are most commonly found in the upper lobes, or apices, of the lungs.
Distinguishing Blebs from Bullae
It is important to distinguish a bleb from a pulmonary bulla, as both are air-filled spaces in the lung. The primary difference is size and location: a bleb is smaller and located on the lung’s surface. A bulla is a larger air-filled cavity, often defined as being greater than one or two centimeters in diameter, and involves the destruction of lung tissue deeper within the organ.
Why Blebs Form
The exact mechanism behind bleb formation is not fully understood, but it is thought to result from subpleural alveolar rupture due to strain overload on the lung’s elastic fibers. The condition is often classified as idiopathic, meaning it arises without a known cause, particularly in young, otherwise healthy individuals.
A classic demographic associated with bleb formation and rupture is young, tall, and thin males, typically between 18 and 40 years old. Researchers suggest the rapid growth during puberty may increase the distending pressure at the top of the lungs, contributing to bleb development. Smoking is a significant risk factor, increasing the risk for a related lung collapse by more than twenty-fold in men and nearly ten-fold in women compared to non-smokers. Genetic disorders involving connective tissue, such as Marfan syndrome or Birt-Hogg-Dube syndrome, can also predispose individuals to developing multiple blebs.
When a Bleb Causes Trouble: Spontaneous Pneumothorax
A lung bleb becomes a medical concern if it ruptures, which leads to a condition called spontaneous pneumothorax, or a collapsed lung. A rupture occurs when the fragile wall of the bleb breaks, allowing air to escape from the lung into the pleural space (the area between the lung and the chest wall).
As air accumulates in this space, it creates pressure that pushes against the lung, causing it to partially or fully collapse. This is termed a primary spontaneous pneumothorax when it occurs in a person without a history of underlying lung disease. The onset of symptoms is typically sudden, including acute, sharp chest pain on the side of the rupture, which may worsen with a deep breath or cough. Shortness of breath (dyspnea) is also a common symptom, and in severe cases, it can be accompanied by a rapid heart rate. Any sudden onset of chest pain and breathing difficulty requires immediate medical evaluation.
How Blebs Are Detected and Managed
Blebs are often discovered incidentally during medical imaging performed for an unrelated reason. A standard chest X-ray is often the first tool used when a pneumothorax is suspected, though small blebs are frequently not visible on this imaging. A computed tomography (CT) scan provides a much more detailed view, clearly showing the thin-walled air sacs, their size, and their exact location.
Management depends on whether the bleb has caused a pneumothorax and the severity of the lung collapse. If a small pneumothorax occurs, it may be managed conservatively with observation and supplemental oxygen to allow the air to be reabsorbed. For larger collapses or recurrent episodes, a chest tube may be inserted to drain the air from the pleural space. To prevent future collapses, surgical intervention is often recommended, typically using Video-Assisted Thoracoscopic Surgery (VATS) to remove the bleb and promote adhesion of the lung to the chest wall.