Address correspondence to: Debra A. Jones, MD, Department of Obstetrics & Gynecology, University of New Mexico School of Medicine, 2211 Lomas Blvd. NE, Albuquerque, New Mexico 87131-5286, Ph: 505-272-6907, Fax: 505-272-6385

Synonyms: Bronchopulmonary sequestration and accessory lung.

Definition: A congenital anomaly characterized by a mass of non-functioning pulmonary parenchyma which is separated from normal lung and receives its blood supply from the systemic circulation and has its own pleura.

Prevalence: 0.15-6.4% of all congenital pulmonary malformations¹. Prevalence is greater in males than females, M:F 4:1.

Etiology: Unknown.

Pathogenesis: The normal tracheobronchial tree derives from an outpouching of foregut. Extralobar sequestered lung occurs either from: 1) A separate outpouching of foregut, or 2) A segment or normally developing lung that has lost its connection from the rest of the lung. Extralobar sequestered lung arises after formation of the pleura and has its own pleura. The arterial supply is usually from the aorta while venous drainage is into the right atrium. Eighty percent occur on the left side². Extralobar pulmonary sequestration is usually found near the lower lobe and diaphragm.

Associated anomalies: Occur in about 50-60% of sequestrations^1,3. Diaphragmatic hernia, pectus excavatum, tracheo­esophageal fistula esophageal duplication, esophageal cyst, bronchogenic cyst, megacolon and congenital heart disease are the most common.

Differential diagnosis: Cystic adenomatoid malformation of the lung, mediastinal teratoma and diaphragmatic hernia.

Prognosis: Dependent on accompanying anomalies. Amenable to surgical intervention if no associated anomalies, with good survival rate^1,2,3. When associated with hydrops there is a 100% mortality.

Risk of recurrence: Unknown, sporadic.

Management: In utero therapy.

MESH Bronchopulmonary-Sequestration BDE 0612 ICD9 748.5 CDC 748.520

Introduction

Prenatal diagnosis of intra­thoracic extralobar lung sequestration is a rare event. Early diagnosis is essential to allow intervention aimed at preventing and reversing hydrops fetalis and pulmonary hypoplasia.

We report a case of prenatal diagnosis and a review of antenatally diagnosed cases of intrathoracic extralobar pulmonary sequestration.

Case report

A 21-year-old G₂P₁ was followed in Maternal-Fetal Medicine Clinic for hyperthyroidism. A routine ultrasound performed at 24 weeks gestation revealed an isolated left hydrothorax. The patient was referred to the Prenatal Diagnosis Division. A work up was begun including maternal serology, echocardiogram, repeat targeted ultrasound, counseling, and fetal blood sampling. The serology was negative. The Rhesus was negative with a negative antibody screen. The fetal scan revealed bilateral hydrothorax with an echogenic mass located in the thorax, ascites, skin edema, and mild polyhydramnios (fig. 1).

Figure 1: Sagittal scan of the fetal thorax demonstrating bilateral hydrothorax and the sequestered lung. Note also evidence of ascites and subcutaneous edema.

The patient was counseled regarding the above findings and underwent cordocentesis and fetal thoracentesis. The fetus was found to be 46XX. The fetal hematocrit was 43%, mean corpuscular volume 115.9, blood type A, Rh positive, Coombs negative. The fetal blood gas pH 7.57, PCO₂ 20 mmgHg, HCO 18mmol/L, 0₂ Sat 78%, delta base - 1.3. Kleinhauer-Betke: >> 99% fetal cells. The parvovirus and cytomegulovirus cultures were negative. Fetal thyroid function studies were normal. The thoracentesis revealed few white blood cellls, total protein less than 1.0 g/dl, suggesting secondary hydrothorax and not chylo­thorax.

The results were discussed with the patient, the neonatologists and the Prenatal Diagnosis Division. A transcutaneous fetal thoraco-amniotic shunt placement was offered. The patient declined shunt placement but wanted all intervention for the fetus and was followed by the Maternal-Fetal Medicine division and prenatal diagnosis team.

At 27 weeks 3 days, the patient was admitted in preterm labor. Evaluation revealed a severely hydropic fetus and polyhydramnios. Tocolysis was started with indomethacin 25 mg orally every 6 hours for 2 days, then oral terbutaline.

At 29 weeks, the patient presented with preterm premature rupture of membranes. The fetus developed signs of fetal distress and required an emergency delivery. A grossly hydropic female infant was delivered with birth weight of 1675 grams. Apgars were at 0 at 1 and 5 minutes, respectively, after failed attempts to ventilate.

The post-mortem evaluation revealed the following (fig. 2):

• Non-immune hydrops fetalis.

• Extralobar pulmonary sequestration 30 x 30 x 15mm in left pleural cavity with arterial supply from abdominal aorta.

• Hypoplastic left lung.

• Immature placenta with edematous chorionic villi.

• Dilated, tense gallbladder secondary to stenotic duct.

Figure 2: Pathological specimen illustrating the sequestered lung.

Discussion

Extrapulmonary lung sequestration is a rare pulmonary anomaly. Prenatal diagnosis of intrathoracic extralobar lung sequestration is a rare event. Early diagnosis is essential to allow intervention aimed at preventing and reversing hydrops fetalis, pulmonary hypoplasia and polyhydramnios, thereby enhancing perinatal survival.

A review on antenatally diagnosed cases of intrathoracic extralobar pulmonary sequestration is provided in Table 1¹¹.

The association of non-immune hydrops fetalis and extralobar lung sequestration is a rare event. A high index of suspicion and prompt in utero therapy is needed to attempt a reduction in the mortality rate.

Embryology

The lower respiratory tract begins to form around the middle of the fourth week of gestation from an outpouching of the laryngotracheal groove. The respiratory tract is a derivative of the primitive gut, specifically the foregut. The accessory lung is felt to originate from a separate outpouching of the foregut or a segment of developing lung that has lost its connection to the rest of the lung. The time of separation is important. The accessory lobe that arises before formation of the pleura is surrounded by the same pleura as normal lung, and is referred to as  intralobar. The accessory bud that arises after the formation of pleura has its own pleura and is referred to as extralobar.

Diagnosis

The first description of an aberrant systemic artery to the lung was by Huber⁴ in 1777. In 1861, two reports of pulmonary sequestration appeared^5,6. The term lung sequestration was coined by Pryce in 1956⁶ after his description established the lesion as a distinct clinical entity. The first antenatal diagnosis of extralobar pulmonary sequestration was in 1986, by Weiner et al⁷. The antenatal sonographic findings of extralobar pulmonary lung sequestration were previously described by Romero et al⁸ in 1982. Sonographically, the sequestered lung appears as an echogenic, non-pulsatile intrathoracic mass. A shift of the mediastinum is commonly seen. The most common location is the basal region of the left hemithorax. The prenatal diagnosis of extralobar pulmonary sequestration is unusual. The diagnosis is usually made postoperatively or at autopsy^1,9. A high index of suspicion may make prenatal diagnosis somewhat easier.

Table 1: Extralobar lung sequestration. Review of the literature.

Differential diagnosis

The differential diagnosis of pulmonary sequestration should include mediastinal teratomas, cystic adenomatoid malformation, and diaphragmatic hernia. Pulmonary sequestration should be part of the differential diagnosis of non-immune hydrops fetalis.

Congenital cystic adenomatoid malformation (CCAML) may be classified as macrocytic (cysts greater than or equal to 5 mm in diameter) or microcytic (cysts << 5 mm). Microcytic cystic adenomatoid malformation may appear solid, making the diagnosis difficult. Sauerbrei¹⁶ has used duplex Doppler imaging to establish the diagnosis of lung sequestration by diligently searching for an anomalous blood supply.

Diaphragmatic hernia may appear as a hyperechoic chest mass. Accurate identification of the diaphragm and visualization of diaphragmatic defect is important in distinguishing a diaphragmatic hernia from extralobar pulmonary lung sequestration.

Prognosis

The perinatal mortality is 100% when lung sequestration is associated with non-immune hydrops fetalis. Early prenatal identification of an accessory lobe with hydrothorax with immediate continuous drainage of the pleural effusion might prevent hydrops fetalis, pulmonary hypoplasia, and polyhydramnios. The pregnancy may progress towards term, thereby enhancing perinatal survival.

Management

In utero therapy

As previously stated, the morbidity and mortality seen with extrapulmonary lung sequestration is dependent on associated anomalies and the presence of non-immune hydrops fetalis. In an effort to reduce the mortality rate associated with extrapulmonary lung sequestration, non-immune hydrops fetalis in utero therapy has been proposed⁷. It has been hypothesized that hydrops fetalis does not result directly from the sequestered lobe itself but rather from a mechanical deformity of the mediastinum produced by the associated hydrothorax⁷. The displacement of the mediastinum can produce an obstruction of the venous return and subsequent low output cardiac failure leading to hydrops fetalis.

Continuous drainage of the hydrothorax via thoracoamniotic shunt should prevent hydrops fetalis^7-15. Early placement of thoracoamniotic shunt should prevent pulmonary hypoplasia⁷. A third advantage of shunt placement is the theoretical prevention of polyhydramnios. The hydro­thorax may cause esophageal obstruction and decrease fetal swallowing.

References

1. Savic B, Birtel FJ, Tholen W, et al. Lung sequestration: Report of seven cases and review of 540 published cases. Thorax 34:96, 1979.

2. Kilman J, Battersby J, Hooshang T, Vellios F. Pulmonary sequestration. Arch Surg 90:648, 1965.

3. Buntain W, Woolley M, Mahour H, Isaac H, Payne V. Pulmonary sequestration in children: A twenty-five year experience. Surgery 81:413, 1977.

4. Huber J. Observationes aliquot de arteria singulari pulmoni concessa. ACTA Helvet 8:85, 1977.

5. Rokitansky C. Lehrbuch per pathogischen anatomie ed 3. Wien, Bienna, 1861, pp 44.

6. Pryce DM. Lower accessory pulmonary artery with intralobar sequestration of the lung. J Pathol 58:459, 1946.

7. Weiner C, Varner M, Pringle K, Hein H, Williamson R, Smith N. Antenatal diagnosis and palliative treatment of non-immune hydrops fetalis secondary to pulmonary sequestration. Obstet Gynecol 68:2, 275, 1986.

8. Romero R, Chervenak F, Kotzen J, Berkowitz R, Hobbin J. Antenatal sonographic findings of extralobar pulmonary sequestration. J Ultrasound Med 1:131, 1982.

9. Stocker J, Hagen-Hallet K. Extralobar pulmonary sequestration, analysis of 15 cases. American Society of Clinical Pathologists 72:917, 1979.

10. Moore K. The Developing Human. Third edition. Philadelphia: WB Saunders, 1982, pp. 216-226.

11. Dolkart L, Reimer F, Helmuth W, Porte M, Eisinger G. Antenatal diagnosis of pulmonary sequestration: A review. OB/GYN Survey. Volume 47, No. 8.

12. Jouppila P, Kirkinen P, Herva R, et al. Prenatal diagnosis of pleural effusion by ultrasound. JCU 11:516, 1983.

13. Kristoffersen SE, Ipsen L. Ultrasonic real-time diagnosis of hydrothorax before delivery in an infant with extralobar lung sequestration. Acta Obstet Gynecol. Scand 63:723, 1984.

14. Thomas C, Leopold G, Hilton S., et al. Fetal hydrops associated with extralobar pulmonary sequestration. J Ultrasound Med 5:668, 1986.

15. Boiskin I, Brunner JP, Jeanty P. Lung extralobar intrathoracic sequestration, torsion. The Fetus 1:7485, 1991.

16. Sauerbrei E. Lung sequestration duplex Doppler diagnosis at 19 weeks gestation. J Ultrasound Med 10:101-105, 1991.

17. Romero R, Pilu G, Jeanty P Prenatal Diagnosis Of Congenital Anomalies. Norwalk, Appleton & Lange, pp 202-205, 1988.