TPPs are most often seen in children and young adults, in whom the thorax is elastic, the visceral pleura intact, and the parenchyma easily injured. Around 85% of cases reported in the literature involved patients below the age of 30 years. Because they are involved more often in motor vehicle accidents and falls, men are affected more than women. In our case report, the patient was 60 years old, which is far from the mean age of patients with TPP. Unlike pulmonary contusions or hematomas, TPPs are rare, developing in less than 3% of patients with pulmonary parenchymal injuries
Santos and Mahendra
 proposed the term “pseudocyst” because the cyst lacks an epithelial lining. The significance and behavior of the TPP depend on the impact velocity, the degree of chest wall displacement, and the elasticity of the chest wall in blunt chest trauma
. It is believed that the more elastic and pliable chest wall of young people and children permits the transmission of kinetic energy more efficiently to the underlying lung parenchyma. The pseudocyst develops via a mechanism that allows the transmission of high compressive force to the lung parenchyma. The concussive forces of a high-velocity impact with low displacement of the chest wall result in a peripheral pseudocyst, whereas the compressive forces of a low-velocity impact with high displacement of the chest wall result in a central pseudocyst
[3, 4]. An intraparenchymal pulmonary laceration with airway disruption and leaking of air into the pulmonary parenchyma occurs in both mechanisms. The mechanism of TPP due to penetrating injury is not clearly described and requires further investigation. It may develop when air, as a result of “one way” or “check valve” mechanism, is able to enter lacerated parenchyma but unable to escape the pleural space.
The action of rapid compression and decompression lacerates alveoli and interstitium, and the concomitant retraction of the surrounding elastic lung tissue leaves small cavities filled with air or fluid or both, which tend to grow until a pressure balance is achieved between the cavity and the surrounding tissue. Another proposed mechanism is that if the glottis is closed or a bronchus is obstructed at the moment of injury, the air in the compressed lung segment fails to exit fast enough and the parenchyma or interstitium lacerates in a “bursting” pattern and forms a cavity. Patients present with hemoptysis, chest pain, and cough, symptoms that are attributable to the pulmonary parenchymal injury but not to the TPP itself
. However, TPP may also be asymptomatic
TPPs are often missed by conventional X-rays, especially if they are obtained when the patient is in the supine position and if the lesion is smaller than 2cm. The diagnostic accuracy of chest radiographies ranges from 24% to 50% of the reported cases
. Post-traumatic pulmonary pseudocysts may be identifiable on chest radiograph, but CT is superior for detecting them. Thoracic CT scan can more precisely define the location and size of the cyst and provide early detection and differential diagnosis. However, a series of chest X-rays taken over several days can be useful to differentiate TPP from other kinds of cystic or cavitary lesions, especially if the clinical history of trauma, as in our case, reveals any contusion.
The majority of TPPs are found on lower lobes. TPPs can be single or multiple, unilateral or bilateral. Those of more than 4cm in diameter are usually seen in patients who have multiple injuries with bilateral lesions, whereas those of less than 4cm are usually unilateral
In our patient, in early CT on the second day of admission, there was a right-lung cavitary lesion that completely resolved on evaluation CT one month later and a strong suspicion for a second cavitary lesion in the posterior and lateral segments of the right lower lobe which completely resolved six months later. Post-traumatic pulmonary pseudocysts usually resolve spontaneously but can be complicated and can require surgery. The indications for diagnostic and therapeutic bronchoscopy include endobronchial bleeding, thick sputum, large air leak, mediastinal emphysema, and lobar collapse
[1, 7, 8]. Urgent thoracotomy and lobectomy may be required in the case of massive hemoptysis, which is usually not life-threatening
The indications for video-assisted thoracoscopic surgery or open surgery include prolonged persistence of an air leak, hemothorax due to pseudocyst rupture, failure of lung expansion, progressive enlargement of the pseudocyst, and compression of functional parenchyma. Actually, TPPs may enlarge with positive-pressure ventilation leading to hypoxemia and respiratory deterioration because of inadequate ventilation. In such patients, video-assisted thoracoscopic surgery or open thoracotomy with tube decompression is necessary
In case of secondary infection and septic course, antibiotic treatment according to sputum culture antibiograms is the first step. The approach to an infected pseudocyst is similar to that for a lung abscess. If an infected pseudocyst is larger than 2cm or there are unremitting signs of sepsis after 72 hours of antibiotics, the pseudocyst should be percutaneously drained
. The indications for surgery are failed conservative treatment, an increase in the size of the pseudocyst, development of complications such as respiratory deterioration, or failure of the pseudocyst to become progressively smaller.
If there is no clinical improvement, early CT-guided catheter drainage should be considered. If, despite the drainage, there is no observed clinical improvement, clinicians could proceed with thoracotomy or thoracoscopy. The average spontaneous time for radiological resolution of TPP is three months.
Cavitary lesions such as cavitating hematomas, lung lacerations, and traumatic pseudocysts detected in patients presenting with trauma may also have a non-trauma-related etiology such as blebs, bullae, congenital cysts, coccidioidomycosis, tuberculosis, hydatid disease, and pneumonia. Particularly in countries where causes of cavitation are endemic, other possible causes should be kept in mind as part of the differential diagnosis. However, clinical or radiological diagnosis of TPP is not difficult. The size, shape, and nature of the wall of the TPP, unlike those of other kinds of cystic or cavitary lesions, change in a relatively short time. Thus, a series of chest X-rays taken over several days can be useful to differentiate TPP from other kinds of lesions, and no extensive examination is necessary
. The history of trauma usually delineates any contusion, but if the cavitary lesion in question does not decrease with time, other etiologies must be considered