Lung Sequestration

Definition and occurrence: Sequestrations are characterized by absence of normal bronchial connections and presence of a systemic arterial supply (occasionally, more than one vessel), usually from the thoracic aorta, but sometimes, the abdominal aorta or other artery [1]. Intralobar sequestrations (ILS), which are contained within the normal lung pleura, almost always occur in the lower lobes (98%) and slightly more frequently on the left, 1.2:1. Males predominate, 1.1:1. Extralobar sequestrations (ELS), which occur equally in both sexes, are enveloped by a separate pleura and are found on the left between the lung and diaphragm in most cases, but on the right, in the mediastinum, or within the abdomen in other cases [2]. In cases of ILS, venous return is usually via the pulmonary vein (rarely a systemic vein), and in ELS, via systemic veins (rarely pulmonary veins) [1]. ILS presents after the first decade in 60% of cases, whereas ELS presents within the first decade in 60% of cases [1].

Systemic artery to normal lung: To complicate matters, the term sequestration has also been applied to portions of normal lung (with normal bronchial connections) that are supplied by a systemic artery from either the thoracic or abdominal aorta. Such lesions are usually discovered in infants, children, or young adults of either sex, and occur in the lower lobes, left or right. Venous return is usually via the pulmonary veins [3,4].

Radiographic features: Extralobar sequestrations are most commonly encountered in infants or young children and usually present as lower lobe solid masses on both chest radiography and CT. CT may effectively show the aberrant vascular supply of the sequestration. Intralobar sequestrations commonly present as recurrent infections in young adults, and may appear as recurrent pneumonia on thoracic imaging studies. Intralobar sequestrations may also be detected incidentally, and usually present as lucent lesions on CT. The key to making the diagnosis of sequestration is demonstration of the lesion's aberrant arterial supply.

Histologic appearance: Whereas in most cases the sequestered parenchyma resembles overdistended normal lung, some cases of both ILS and ELS show histologic features of CPAM type 2, at least focally [2,5,6]. Combined CPAM and ELS is usually seen in fetuses or newborns up to 3 months old, whereas ELS alone tends to occur in older children and young adults [2]. Hypertensive vascular changes may occur in the systemic arteries early in life in both ILS and ELS.

normal

Figure 1. Gross Appearance of ILS

Slice of a left lower lobe ILS removed from a 19-year-old woman with recurrent pleuro-pulmonary infections. Aortogram showed an artery from the abdominal aorta. Venous drainage was into the pulmonary vein.

Cystic spaces occupy most of this slice. A small portion of an uninvolved segment lies at the upper left of the specimen. No capsule separates the sequestration from normal lung.

Find the normal lung.

Figure 2. Histologic Appearance

In contrast to the CPAM, sequestrations typically show distended, but generally normal, architectural features. Superimposed evidence of inflammation is common.

Here, a bronchiole, a respiratory bronchiole, and dilated alveolar spaces are shown. Patchy inflammatory exudate and interstitial inflammation are present.

Figure 3. Dilated Airway

A dilated airway lies to the right of overdistended lung parenchyma. Again, there is patchy chronic inflammation.

Figure 4. Organizing Alveolar Exudate

 

Pathogenesis: Although ELS is a congenital lesion, ILS has been considered to be an acquired lesion in response to chronic infection, with subsequent development of bronchial stenosis and secondary acquisition of a systemic artery via the pulmonary ligament. This hypothesis is based, in part, on its rarity in the fetus or newborn [5]. However, recent reports of ILS in the fetus indicate that it can be a congenital abnormality [5,6], and the acquired nature of the adult form remains unproven.

Diagnosis: Symptoms in the newborn are similar to those in patients with CPAMs. Presentation with dyspnea occurs early in life; signs of infection occur later. There are reports of fetal ILS without demonstrable systemic blood supply by ultrasound [6], making surgical intervention important for diagnosis of both CPAM and sequestration. If the sequestration is connected to foregut structures, it is called a bronchopulmonary foregut malformation [7].

Associated abnormalities: Other anomalies are rare with ILS and include diaphragmatic hernia and skeletal malformations. In ELS, other anomalies, mostly diaphragmatic hernia, pulmonary hypoplasia because of in utero compression of normal lung, and congenital heart disease, occur in 22% of patients [2].

References: To return to reference section after viewing abstract, click here before clicking on "abstract".

1. Savic B, Birtel F, Knoche R, Tholen W, Schild H. Pulmonary sequestration. Ergeb Inn Med Kinderheilkd 1979; 43:57-92.

2. Conran R, Stocker J. Extrolobar sequestration with frequently associated congenital cystic adenomatoid malformation, type 2: report of 50 cases. Pediatr Developmental Pathol 1999; 2:454-463. Abstract

3. Yamanaka A, Hirai T, Fujimoto T, Hase M, Noguchi M, Konishi F. Anomalous systemic arterial supply to normal basal segments of the left lower lobe. Ann Thorac Surg 1999; 68:332-338. Abstract

4. Holder P, Langston C. Intralobar pulmonary sequestration (a nonentity?). Pediatr Pulmonol 1986; 2:147-153. Abstract

5. Walford N, Htun K, Chen J, Liu Y, Teo H, Yeo G. Intralobar sequestration of the lung is a congenital anomaly: anatomopathological analysis of four cases diagnosed in fetal life. Pediatr Dev Pathol 2003. Abstract

6. Cass D, Crombleholme T, Howell L, Stafford P, Ruchelli E, Adzick N. Cystic lung lesions with systemic arterial blood supply: a hybrid of congenital cystic adenomatoid malformation and bronchopulmonary sequestration. J Pediatr Surg 1997; 32:986-990. Abstract

7. Hruban R, Shumway S, Orel S, Dumler J, Baker R, Hutchins G. Congenital bronchopulmonary foregut malformations. Intralobar and extralobar pulmonary sequestrations communicating with the foregut. Am J Clin Pathol 1989; 91:403-409. Abstract

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