Intraabdominal Bronchopulmonary Sequestration

Intraabdominal BPS is a rare congenital malformation consisting of a non-functioning bronchopulmonary mass which is not connected to the main tracheobronchial tree. The mass receives arterial blood supply directly from the systemic circulation and is located within the abdomen.

Bronchopulmonary sequestration (BPS), cystic lung lesion, accessory pulmonary lobe, pulmonary aberration, supernumerary lung, Nebenlunge, Rokitansky lobe.

Q33.2 sequestration of lung

10-15% of extralobar pulmonary sequestrations are located below the diaphragm. 1-2 The incidence of Intraabdominal BPS is approximately 1: 10,000.3 The male to female ratio is 4:1. 4

Pulmonary sequestration (PS) falls within the spectrum of bronchopulmonary foregut anomalies and is characterised as non-functional pulmonary tissue separated from normal bronchial connections. Two types of PS have been described: intralobar sequestrations, which account for 75% of pulmonary sequestrations and extralobar sequestrations, which account for 25% of cases. Many theories have been suggested for the development of sequestration and its related malformations; however, no hypothesis has been universally accepted. The most plausible theory suggests that a supernumerary lung bud develops below the normal lung bud.5 If the lung bud arises before the development of pleura, it results in intralobar sequestration. If the lung bud continues to migrate caudally with the oesophagus, it develops into extra lobar sequestration and derives its blood supply from the primitive splanchnic vessels surrounding the foregut. 6   

Masses characteristic of intraabdominal pulmonary sequestrations are typically oval or pyramidal in shape, and measure between 0.5-1.5 cm in dimension. 7 Histologically, the lung parenchyma in the sequestered segment displays evidence of lymphocytic inflammation and fibrosis with cystic air spaces lined by cuboidal or columnar epithelium. Other histological findings which are found in 85% of cases include alveoli with emphysema-like hyperinflation and dilated lymphatic vessels in the subpleural region. 

Associated anomalies are found in approximately 50% of cases. The most common malformation seen is a congenital diaphragmatic hernia. Other malformations include eventration of the diaphragm, gastrointestinal fistula, foregut anomalies, thoracic and abdominal enteric duplication cysts, pectus excavatum, congenital heart defects, and vertebral anomalies. 8 Additional lung anomalies are found in 25% of cases, including lung hypoplasia, congenital cystic adenomatoid malformation (CCAM), congenital lobar emphysema or a bronchogenic cyst.9

BPS is thought to be a sporadic abnormality with a very low risk of recurrence in subsequent pregnancies. Rare familial cases have been reported which suggests that there may be a genetic component in some cases. 10,11,12 

Intraabdominal BPS is often diagnosed in the second trimester during the foetal anatomic survey which is commonly performed between 18-22 weeks of gestation. On ultrasound, the lesion appears as a well-circumscribed homogenous, hyperechoic solid mass. The mass may be elliptical in shape and may have small cystic areas within it. Many of these masses display a “sliding sign” which is defined as a mass that shifts during foetal breathing movements.13 These lesions are more commonly seen in the left suprarenal region (86%).

The key feature in diagnosis is colour Doppler imaging which reveals a feeding artery from the abdominal aorta. When Intraabdominal BPS is suspected, focus on the relationship between the feeding artery and the abdominal aorta or its branches in multiple views should be taken. Visualisation of the feeding artery can be challenging and ultrasound views should be adjusted as necessary and not limited to the standard coronal, horizontal, and sagittal sections. The arterial supply is commonly from the aorta, but can also arise from the celiac axis. If arterial blood supply can be confirmed, this finding supports a correct diagnosis. The venous drainage pattern can also be assessed. The mass typically drains to the azygous, portal, oesophageal, or adrenal veins or directly into the right atrium. 14 

Intraabdominal BPS may displace the stomach anteriorly. Care should be taken to ensure that the adrenal gland is normal, and that the mass does not arise from the kidney, spleen, adrenal gland or bowel. 

MRI can be considered, but is not necessary to confirm the and rarely changes antenatal management. 
 

Several entities must be considered in addition to pulmonary sequestration when an echogenic mass is visualised beneath the diaphragm. These include neuroblastoma, adrenal hemorrhage, mesoblastic nephroma, retroperitoneal teratoma, and lymphangioma.

Neuroblastoma: 
A neuroblastoma typically has poorly defined margins. The mass is typically hypoechoic or has mixed echogenicity. Calcifications can be seen inside the mass. Neuroblastomas are more often cystic, right-sided, and seen initially in the third trimester. Color Doppler imaging of neuroblastomas can reveal peripheral vascularisation or no blood flow inside of a cystic mass.15 Neuroblastoma often invades the adjacent organs and does not demonstrate the “sliding sign”. For further description, please see the VISUOG chapter on neuroblastoma. 

Adrenal haemorrhage: 
Adrenal haemorrhage is seen as a mass above the foetal kidney. Its echogenicity changes with time and may be initially either hyperechoic, isoechoic or hypoechoic depending on the age of the haemorrhage. Adrenal haemorrhage may also be seen as an anechoic, cystic area with or without septations. On colour Doppler imaging, there is no internal blood flow. They can occur unilaterally or bilaterally. The right adrenal gland is involved in 75% of cases.

Mesoblastic nephroma: 
Mesoblastic nephromas are usually seen as a well-defined solid mass with homogeneous, slightly hyperechoic echogenicity when compared to the normal renal parenchyma. They are commonly located near the renal hilum. The mass moves with the kidney during foetal breathing movements. They are highly vascular on colour Doppler imaging. 

Retroperitoneal teratoma: 
These lesions are irregular in shape and size and have a mixed solid and cystic appearance on ultrasound. They are more common in females with a ratio of 4:1.

Lymphangioma: 
These lesions are usually avascular, multiseptated, multicystic irregular masses. These are usually located on the neck (75%), axillary region (20%), chest wall, abdominal wall and extremities (5%). In <1% of cases the tumour is in the mesentery or retroperitoneum.

When an intraabdominal BPS is suspected, a thorough evaluation of the rest of the foetus should be performed to look for additional abnormalities. Special attention should focus on evaluation of the foetal diaphragm, heart, lungs kidney, adrenal, vertebrae and bowel so that abnormalities of these structures are identified.  

The prenatal natural history of intraabdominal BPS is not well defined. Most lesions are thought to reach a peak size between 26-28 weeks’ gestation and then either remain the same size or decrease in size to term. Some case reports have reported that large lesions may be associated with fetal hydrops, which is defined as fluid in two or more body cavities including hydrothorax, pericardial effusion and ascites. 

In the later part of the pregnancy, some of these lesions can be difficult to visualise due to foetal position. This should not be assumed to represent spontaneous regression. These lesions should be followed in the postnatal period by CT scan/MRI.    

Foetuses with intraabdominal BPS should be monitored with serial ultrasounds in pregnancy to monitor growth of the foetus, the size of the mass and to screen for foetal hydrops. 

The prognosis for patients with Intraabdominal BPS is generally favourable and rarely requires foetal intervention. Foetuses with associated congenital anomalies may have a worse prognosis.16 
More than 95 percent of foetuses affected by intraabdominal BPS survive. Poor prognostic features include large lesion size, and associated hydrops. Because of the systemic arterial supply and venous drainage, large lesions may develop severe left to right shunts, leading to high-output cardiac failure. 

Prenatally, Intraabdominal BPS should be followed-up with regular ultrasounds to assess the growth of the lesion and development of hydrops. The ultrasound frequency would depend on the size of the lesion. Larger lesions should be reassessed more frequently. 

The incidence of chromosomal abnormalities is not increased in these cases above the baseline. However, an amniocentesis with microarray testing should be offered in patients with associated anomalies as the risk of an underlying chromosomal abnormalities may be increased in these cases. 

Most foetuses with intraabdominal pulmonary sequestrations do not require intervention during the pregnancy. However, hydrops is a sign of poor prognosis, and management depends on the gestational age at diagnosis and severity of hydrops. If the gestational age at diagnosis is at least 32-34 weeks, delivery after corticosteroid-induced lung maturation can be considered. For pregnancies between 20-32 weeks, foetal intervention can be considered to allow for in-utero maturation of the foetus. Interventions can include percutaneous laser ablation of the feeding vessel, thoracocentesis or thoracoamniotic shunt placement.  

Delivery planning should be in conjunction with neonatologist and paediatric surgeons. Large lesions may require delivery at the tertiary centre with neonatal intensive care facilities. BPS itself is not an indication for early delivery. Cesarean delivery should be performed only for the usual obstetric indications. 

The majority of infants with small lesions are asymptomatic at birth. However, all cases should be evaluated by postnatal imaging, including cases that appeared to have resolved during the antenatal period as postnatal imaging (CT Scan/MRI) is more sensitive than prenatal ultrasound for detecting small lesions.

The treatment of Intraabdominal BPS after birth is controversial. Since spontaneous regression is possible 16-17, conservative therapy has been advocated. Today, surgical resection remains the treatment of choice because complete excision can eliminate the potential risks of complications including infection, torsion or malignant degeneration. Malignancy is rare; only 2 cases of squamous cell carcinoma have been reported.18-19 

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2. Laje P, Martinez-Ferro M, Grisoni E, Dudgeon D. Intraabdominal pulmonary sequestration. A case series and review of the literature. J Pediatr Surg. 2006;41(7):1309-1312. 
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13. Xu G, Zhou J, Zeng S, et al. Prenatal diagnosis of fetal intraabdominal extralobar pulmonary sequestration: a 12-year 3-center experience in China. Sci Rep. 2019;9(1):943. 
14. Vijayaraghavan SB, Rao PS, Selvarasu CD, Rao TM. Prenatal sonographic features of intralobar bronchopulmonary sequestration. J Ultrasound Med. 2003;22(5):541-544. 15. Curtis MR, Mooney DP, Vaccaro TJ, et al. Prenatal ultrasound characterization of the suprarenal mass: distinction between neuroblastoma and subdiaphragmatic extralobar pulmonary sequestration. J Ultrasound Med. 1997;16(2):75-83.
16. Riley JS, Urwin JW, Oliver ER, et al. Prenatal growth characteristics and pre/postnatal management of bronchopulmonary sequestrations. J Pediatr Surg. 2018;53(2):265-269. 18. Chowdhury M, Samuel M, Ramsay A, Constantinou J, McHugh K, Pierro A. Spontaneous postnatal involution of intraabdominal pulmonary sequestration. J Pediatr Surg. 2004;39(8):1273-1275. 
17. Costa MR, Costa TR, Leite MS, et al. Apresentação atípica de sequestro pulmonar extralobar intra-abdominal detectado no pré-natal: relato de caso [Atypical presentation of intra-abdominal extralobar pulmonary sequestration detected in prenatal care: a case report]. Rev Paul Pediatr. 2016;34(2):243-246.
18. Bell-Thomson J, Missier P, Sommers SC. Lung carcinoma arising in bronchopulmonary sequestration. Cancer. 1979;44(1):334-339.
19. Hertzog P, Roujeau J, Marcou J. J Fr Med Chir Thorac. 1963;17:33-38.

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