Bilateral Paramediastinal Post- Traumatic Lung Cysts: DISCUSSION
Posted by James
To our knowledge, this case is the first report of bilateral post-traumatic paramediastinal lung cysts. Furthermore, it illustrates several characteristic features of this condition. All patients have a history of blunt chest trauma, which may be minor. Over 80 percent are 30 years of age or less, with no previous pulmonary complaints. Many patients present with hemoptysis, chest pain, cough, and dyspnea. There may be a low-grade fever with mild leukocytosis.
A number of factors have been implicated as important mechanisms of injury. Initially, a blunt force applied to the chest wall results in compression and high pressures within the underlying pulmonary parenchyma. This may lead to the rupture of small bronchi, causing the surrounding alveoli to burst. Air can then enter between the layers of the pulmonary ligament. Rupture of capillaries around the lacerated alveoli then leads to accumulation of blood within the newly formed air space. A closed glottis may play a role in producing high intrathoracic pressure from chest compression. The bursting process may involve any area of either lung, although the apices are usually spared. An alternative theory proposes that a blow to the chest wall creates a concussive wave, leading to shearing stresses which exceed the elasticity of the pulmonary tissue. Still another proposal notes that increased intrathoracic pressure may be followed by negative pressure due to elastic recoil after compression. This might produce bursting followed by shearing forces, leading to parenchymal lacerations, and escape of air and fluid into the lung.