Address correspondence to: Thomas C. Wheeler, MD, Vanderbilt University Medical Center, Dept. of Obstetrics and Gynecology, Division of Maternal‑Fetal Medicine, 21st and Garland, Nashville, TN 37232‑2516 Ph: 615‑343‑7234 FAX 615‑343‑8881.

Synonyms: Bronchopulmonary forgut malformation, accessory lung, Rokitansky lobe, aortic pulmonary lobe.

Prevalence: Subdiaphragmatic extralobar sequestration: 1:10,000¹. Approximately 10%-15% of extralobar sequestrations are found within or below the diaphragm². There is no familial predisposition. M4:F1.

Definition: Extralobar subdiaphragmatic lung sequestration: A mass of non-aerated pulmonary tissue that is not connected to the normal bronchial tree and is located beneath the diaphragm. It receives its own blood supply from a systemic artery, it is enveloped by its own pleura, and its venous drainage is to the systemic veins.

Etiology: Controversial; likely a variation of the broncho-pulmonary-forgut malformations.

Pathogenesis: An anomalous or supernumerary lung bud that derives its blood supply from the primitive splanchnic vessels that surround the foregut. These vessels migrate distally with the foregut and provide the blood supply to the sequestration. The original connection with the foregut typically involutes but may persist, allowing communication with the gastrointestinal tract³. Torsion of the sequestration or venous compression may result in excesss lymphatic drainages, resulting in hydrops. Obstruction of the gastrointestinal tract may manifest as polyhydramnios.

Associated anomalies: Incidence 58%¹. Diaphragmatic defects, gastric and colonic duplications, congenital cystic adenomatoid malformation, vertebral abnormalities, and cardiac defects. There are no associated chromosomal abnormalities.

Differential diagnosis: Neuro­blastoma, retroperitoneal teratoma, adrenal tumor/hemorrhage, mesonephroma, and foregut duplication.

Prognosis: Dependent upon associated anomalies. Poor survival noted with pulmonary hypoplasia, secondary to diaphragmatic hernia.

Recurrent risk: Unknown.

Management: Prenatally: in the absence of hydrops, expectant management is recommended. Duplex Doppler may provide additional information regarding the blood supply to the mass⁴. Postnatally: urinary catecholamines, angiography, and an upper gastrointestinal series may assist with surgical management.

MESH Bronchopulmonary‑sequestration BDE 0612 ICD9 748.5 CDC 748.525

Introduction

Pulmonary sequestraton is a relatively rare congential anomaly first noted in the medical literature in 1861 by Rokitansky and Rektorzik⁵. The first report of antenatal diagnosis of this anomaly followed some 120 years later with sonographic recognition of an extralobar pulmonary sequestration^6-9. Subdiaphragmatic sequestrations are a rare form of bronchopulmonary foregut malformation occurring in just two percent of the cases in the largest reported series¹. We report on 5 such cases discovered at various points in gestation.

Case 1

A 21-year-old, was referred for evaluation of uterine size greater than dates at 31 weeks gestation. Fetal biometry was appropriate, and amniotic fluid volume was increased. The exam was remarkable for a 20x30x20 mm echogenic mass extending across the posterior mediastinum (fig. 1-3), suggesting an infradiaphragmatic pulmonary sequestration.

Fig. 1: Case #1: A hyperechoic mass, located in front of the aorta, extends towards the left and right sides.

Fig. 2: Case #1: The cranial extension of the mass reaches behind the heart.

Fig. 3: Case #1:  Sagittal view of the extralobar sequestration.

Follow‑up examinations demonstrated appro­priate growth without evidence of hydrops. The patient delivered at term a 3880g fetus. A thymic sail sign was recognized on chest X‑ray, while the chest CT was suggestive of a neuroblastoma or a foregut duplication. Laparotomy was performed on postpartum day 5 with pathology confirming pulmonary sequestration. The postoperative course was uneventful, and the baby was discharged on postoperative day 5.

Case 2

A 27-year-old G₄P₀₀₃₀ was referred when a screening ultrasound revealed an echogenic mass in the left lower chest. A 20x30 mm polycystic mass was noted in the posterior left hemithorax which displaced the adrenal gland inferiorly and displaced the spleen and the stomach anteriorly (fig. 4-5).

Fig. 4: Case #2: Hyperechoic mass below the diaphragm, anterior to the spleen and medial to the stomach. Two cysts are seen in the mass.

Fig.54: Case #2: A longitudinal view demonstrates the relation of the mass and the aorta.

There was a suggestion of a vascular pedicle originating from the aorta. The findings suggested an infradiaphragmatic pulmonary sequestration. A 4260g male fetus was delivered at term and was taken to the NICU for respiratory distress. A pneumothorax was diagnosed and treated with a chest tube. A chest CT confirmed the antenatal findings. The neonate was readmitted on postpartum day 12, and exploratory laparotomy confirmed a retroperitoneal pulmonary sequestration. He was discharged on postoperative day 4.

Case 3

A 22-year-old insulin‑dependent diabetic was referred when a screening ultrasound noted an echogenic mass superior to the left kidney (fig. 6-7).

Fig. 6: Case #3: The feeding vessel is seen.

Fig. 7: Case #3: The adrenal gland (arrow) is seen lateral to the mass.

Follow‑up evaluation was suggestive of an extra‑ thoracic pulmonary sequestration. A 3600g male was delivered by cesarean section and taken to the NICU for observation. An abdominal ultrasound demonstrated a hyperechoic mass separate from the left adrenal gland with duplex Doppler demonstrated flow originating from the aorta. Laparotomy was performed on postpartum day 2, and pulmonary sequestration was confirmed by pathology.  The postoperative course was uneventful, and he was discharged seven days later.

Case 4

A 34-year-old with twin gestation underwent multiple ultrasound evaluations due to suspected growth discordancy. At 24 weeks gestation, twin A was noted to have an echogenic, suprarenal mass that appeared to wrap around the aorta and extend across the abdomen (fig. 8-9).

Fig. 8: Case #4: Hyperechoic mass below the diaphragm, anterior to the spleen and medial to the stomach.

Fig. 9: Case #4: coronal view of the mass and the aorta.

Differential diagnosis included neuroblastoma, teratoma, and pulmonary sequestration. The twins were delivered at term. Twin A was a 2870g male and twin B a 3630g female. The smaller twin was observed in the NICU, where abdominal ultrasound confirmed the antenatal findings and duplex Doppler demonstrated high impedence flow. Urinary meta­nephrines were not suggestive of a neuroblastoma. The neonate was readmitted on postpartum day 21 for laparotomy. The pathology specimen was a pulmonary sequestration with cystic adenomatoid changes. The patient was discharged on day 4.

Case 5

A 22-year old G₁P₀ with gestational diabetes was referred for evaluation when a screening ultrasound noted a hyperechoic mass above the left kidney. Evaluation demonstrated a 20x20 mm subdiaphragmatic mass with no other anomalies (fig 10-11).

Fig. 10: Case #5: Hyperechoic mass below the diaphragm and anteromedial to the spleen.

Fig. 11: Case #5: coronal view of the mass and the aorta.

The findings again suggested an infradiaphragmatic pulmonary sequestration. A 3360g female fetus was delivered at term. Abdominal ultrasound confirmed the antenatal findings, but the parents chose expectant management, and she was discharged on postpartum day 2. Her pediatric course has been uneventful.

Discussion

Subdiaphragmatic pulmonary sequestrations may be an isolated finding or part of a constellation of anomalies. A large majority of patients are symptomatic and are diagnosed within the first six months of life; however, ten percent are found incidentally in asymptomatic individuals¹⁰. The sequestrations were isolated findings in all five of our cases. The four neonates who underwent surgery have had uncomplicated postoperative courses, and case number 5 has been followed expectantly.

Diagnosis

The typical appearance of a subdiaphragmatic sequestration is a nonpulsatile, homogenous, well circumscribed, hyperechoic mass in the fetal abdomen or retroperitoneum. Ninety percent of extralobar sequestrations are localized to the left side of the fetal addomen¹. Cystic areas are commonly found within the lesion. Duplex Doppler may be helpful to demonstrate the systemic arterial blood supply, while color flow doppler can define the venous drainage pattern.

Embryology

The normal lung develops from the primitive laryngotracheal groove, which arises on the ventral aspect of the primitive foregut between five and six weeks embryologic development. The lung bud undergoes multiple divisions to give rise to the tracheobronchial tree. An aberrant lung bud may develop in the embryonic foregut distal to the tracheobronchial bud. This pluripotential mass of tissue migrates distally, with its blood supply giving rise to the sequestration¹¹. Late origination from the elongated foregut results in an extra‑ lobar sequestration invested in its own pleura (fig. 12). The original connection with the foregut typically involutes, but persistance will allow communication with the gastrointestinal tract³.

Fig. 12: Intra- and extralobar sequestration. The infradiaphragmatic sequestration not only is extralobar (it has its own pleura) but is also located below the diaphragm.

Pathology

Microscopically, extralobar sequestrations resemble normal lung except that there is diffuse dilatation of parenchymal structures. The bronchioles, alveolar ducts, and alveoli are dilated and tortuous. Congenital cystic adenomatoid malformation has been described in 15‑25% of extralobar sequestrations¹². Gross examination typically reveals a single ovoid or pyramidal lesion ranging from three to six centimeters in size. The blood supply typically arises from the systemic arteries. Vascular supplies originating from the thoracic or abdominal aorta have been noted in 80% of cases. Venous drainage of extralobar sequestrations are usually through the azygous and hemiazygous system¹².

Differential diagnosis

Several entities must be considered in addition to pulmonary sequestration when an echogenic mass is visualized beneath or within the diaphragm. Neuroblastoma, teratoma, adrenal hemorrhage, or foregut duplication should be considered in the differential diagnosis13. Multiple cysts within the mass may be noted with associated cystic adenomatoid malformation. Duplex and color flow Doppler may provide additional information by demonstrating vascular flow from the abdominal aorta<M^C1>4.

Therapy and prognosis

Prenatal intervention was neither indicated nor required in the 5 cases presented. Intrauterine drainage of large pleural effusions associated with an extralobar sequestration has been shown to reverse fetal hydrops^11,14. In the postpartum period, surgical resection is usually performed in elective fashion. Some authors advocate observation rather than immediate operation as an acceptable alternative. If the sequestration is non‑aerated and angiography is pathognomic, then conservative management is acceptable¹⁵. The prognosis for patients with subdiaphragmatic pulmonary sequestration is generally favorable. Associated congenital anomalies carry a worse prognosis, particularly if there is associated pulmonary hypoplasia.

References

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2. Lager DJ, Kuper KA, Haake GK. Subdiaphragmatic extralobar pulmonary sequestratiojn. Arch Pathol Lab Med 115:536‑38, 1991.

3. Gerle RD, Jaretzki A, Ashley CA. et al.:  Congenital bronchopulmonary foregut malformation: pulmonary sequestration communicating with the gastrointestinal tract. N Engl J Med 278:1413‑19, 1968.

4. Sanerbrei E. Lung sequestration: Duplex Doppler diagnosis at 19 weeks gestation. J Ultrasound Med 10:101‑5, 1991.

5. Rokitansky C, Von Lehrbuch D: Pathologischen Anatomie, Braumuller, Wein P. 44, 1861.

6. Romero R, Chervenak FA, Kotzen J, et al: Antenatal sonographic findings of extralobar lung sequestration. J Ultrasound Med 1:131‑2, 1982.

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9. Stern E, Brill P, Winchester P, et al.: Imaging of prenatally detected intra‑abdominal extralobar sulmonary sequestration. Clin Imaging 14:152‑6, 1990.

10. Rosado de Christenson M, Frazier A, et al.: Extralobar sequestration: radiologic‑pathologic correlation. Radiographics 13:425‑41, 1993.

11. Boiskin I, Bruner J, Jeanty P.: Lung, extralobar intrathoracic sequestration. torsion. The Fetus, 1:2, 1991.

12. Stocker JT, Sequestrations of the lung. Semin Diagn Pathol 3:106‑121, 1986.

13. Brink DA, Balsara ZN. Prenatal ultrasound detection of intra‑abdominal pulmonary sequestration with postnatal MRI correlation. Pediatr Radiol 21:227, 1991.

14. Weiner C, Varner M, Pringle K, Hein H, et al. Antenatal diagnosis and pallaiative treatment of non immune hydrops fetalis secondary to pulmonary extralober sequestration. Obstet Gynecol 68:275‑80, 1986.

15. Bolman RM, Wolfe WG. Bronchiectasis and bronchopulmonary sequestration. Surg Clin North Am 60:867‑81, 1980