A lung hernia, defined as the protrusion of the tissue of the lung through a defect in the thoracic wall, is a rare clinical entity that may develop after sudden increases in intrathoracic pressure, together with predisposing conditions that disrupt the normal anatomical structure of the chest wall. Congenital abnormalities, infections, tumors, surgical procedures, and trauma are some of the most common causes. Imaging studies are needed to confirm the diagnosis.
Protrusion of the lung parenchyma through a tear in the chest wall is termed lung herniation, or a lung hernia, which is not commonly seen in clinical practice  . It is established that extreme and sudden increases in the intrathoracic pressure on one hand (eg. sneezing, heavy weight-lifting, long-term steroid use in chronic obstructive pulmonary disease, or playing a musical instrument), and a pre-existing weakness of the chest wall on the other, must be present in order for a lung hernia to develop     . The broad classification of lung hernias is based on two features: the anatomical location (as protrusion through the diaphragm- diaphragmatic, the intercostal spaces- thoracic, and the cervical portion of the chest wall may be seen) and the etiology, further divided into spontaneous and secondary to congenital defects and acquired causes (trauma, infections, tumors, etc.) . The term "pathological hernia" is used to describe lung herniation induced by conditions such as tuberculosis, focal bacterial infections (empyema or osteomyelitis), and malignant diseases . About half of all lung hernias, however, appear after trauma to the chest . Patients may be asymptomatic (typical for uncomplicated spontaneous hernias), but a subcutaneous mass that is soft and tender on palpation and often enlarges after a Valsalva maneuver is the typical clinical presentation  . Chest pain and recurrent infections are common symptoms as well .
Lung hernias are frequently diagnosed months or even years after the initial pathological event due to the asymptomatic course until the repetitive sudden rise in intrathoracic pressure causes a more pronounced clinical presentation  . The workup should start with a detailed patient history that will evaluate recent trauma, surgical procedures such as thoracotomy, or preexisting strenuous activities that may have led to the appearance of symptoms. A thorough physical examination must be performed soon after, and a careful inspection and palpation of the chest can often be sufficient to detect a visible defect and the protrusion of lung tissue as a soft and tender mass. To confirm the diagnosis, however, imaging studies are the cornerstone. Plain radiography is a useful first-line method that can show protrusion of the lungs beyond the rib cage and a wider intercostal space . Anteriorly, the space between the eighth and ninth rib is considered to be a common place for lung hernias to occur (due to the absence of intercostal muscles), while the area from the vertebrae to the costal angle is observed as a vulnerable site posteriorly . Ultrasonography is also regarded as a good method by some authors , but computed tomography (CT) is widely recognized as the gold standard for evaluation of lung hernias . The exact location, the severity of protrusion, as well as the assessment of adjacent soft tissues, is performed in a superior manner by CT compared to X-rays and ultrasonography    .