Pulmonary sequestration is a congenital anomaly characterized by the formation of aberrant, non-functioning lung tissue. It is classified into two types: intralobar and extralobar, each with distinct clinical and radiological features. Although it is more frequently diagnosed in neonates and young children, its diagnosis in adults is rare and is often associated with a history of recurrent pulmonary infections.

• Intralobar type (ILS): accounting for 75% of cases, its main characteristic is that it shares the same visceral pleural lining as the native lung.
  

  Fig 1: Illustration of ILS. Its main characteristic is that it shares the same visceral pleura lining as the native lung.
• Extralobar type (ELS): accounting for 25% of cases, this type has its own visceral pleura, which differentiates it from the normal pulmonary lobe.
  

  Fig 2: Illustration of ELS. This type has its own visceral pleura, which differentiates it from the normal pulmonary lobe.

Another difference is the embryologic origin. The most accepted theory is that the intralobar type occurs if the lung bud arises before the development of the pleura, whereas the extralobar type occurs if the accessory supernumerary lung bud continues to migrate caudally with the esophagus.

Even though the classification of pulmonary sequestrations divides them into two types according to the involvement of the visceral pleura, there are other characteristics that can be visualized, such as venous drainage into pulmonary or systemic structures. For this reason, a clear differentiation between them is often difficult due to the mixed types of venous drainage.