Intralobar Sequestration

Jud W. Gurney, MD, FACR

Key Facts

Terminology

Pulmonary sequestration represents nonfunctioning lung tissue separated from normal lung
- Receives its blood supply from systemic artery
Intralobar sequestration (90%)
Extralobar sequestration (10%)

Imaging Findings

95% lower lobes
Persistent left-sided inferior paraspinal opacity with history of recurrent pneumonia
- Cystic-bronchiectatic form
- Pseudotumor form
- Emphysematous form
Lung bordering sequestration often hyperinflated or emphysematous
Systemic artery
- Origin: Thoracic aorta (75%)
- Origin: Abdominal aorta (20%)
- Artery can measure up to 1 cm in diameter, often shows intimal calcification
Venous drainage via inferior pulmonary vein

Top Differential Diagnoses

Clinical Issues

Persistent opacification in same portion of lower lobe should raise suspicion for diagnosis

Coronal CECT reconstruction shows sequestration

surrounded by hyperlucent lung

and fed by arteries

crossing the hemidiaphragm.

Axial CECT shows a small artery

that had arisen from the aorta adjacent to the hemidiaphragm.

TERMINOLOGY

Definitions

Malinosculation: Congenital abnormal connection of 1 or more of 4 components of lung (airways, arterial supply, venous drainage, and parenchyma)
Pulmonary sequestration represents nonfunctioning lung tissue separated from normal lung
- Receives its blood supply from systemic artery
- Normal communication with bronchi lost
2 major forms
- Intralobar sequestration (90%)
  - Shares visceral pleura of normal lung
- Extralobar sequestration (10%)
  - Has separate pleura from normal lung
- Communicating bronchopulmonary foregut malformation is uncommon form of sequestration, usually seen with extralobar type

IMAGING FINDINGS

General Features

Best diagnostic clue: Persistent left-sided inferior paraspinal opacity with history of recurrent pneumonia
Patient position/location
- 95% lower lobes
  - Left lower lobe (65%), right lower lobe (55%)
  - Posterior basal segment > medial basal segment
Size: Variable, but cystic lesions often quite large

CT Findings

Radiographic Findings

Inferior paraspinal mass or opacity located in posterior basal segment adjacent to diaphragm
- Margins may be either sharp, lobulated, or ill-defined
Concurrent volume loss common
1/3 of cystic sequestrations contain air or air-fluid levels
- Localized emphysema without consolidation or fluid is well described but uncommon
Chronic or recurrent bacterial pneumonia
- May decrease in size with antibiotic therapy, but will not resolve
Pleural effusion (4%) and calcifications rare

MR Findings

Excellent depiction of complex cystic, solid, and fibrotic components
- Cysts have variable signal depending on fluid
  - Often higher signal on T2WI sequences
Hemorrhage within lesion represented by high signal on both T1WI and T2WI sequences

Angiographic Findings

Traditional method of diagnosis but now replaced by CT angiography
Used to embolize feeding arteries
Origin of feeding artery
- Thoracic aorta (75%)
- Abdominal aorta (20%)
- Intercostal artery (5%)
- Multiple (16%)
  - Vessels < 3 mm likely 1 of multiple supplying arteries
95% have pulmonary venous drainage
- 5% systemic venous drainage, usually via azygos, hemiazygos, superior vena cava, or intercostal routes

DIFFERENTIAL DIAGNOSIS

Extralobar Sequestration

Congential lesion, often presents in 1st 6 months
- Completely distinct entity from intralobar form
Associated with other congential anomalies
Systemic arterial supply from aorta
- Drainage into systemic veins (80%), not pulmonary
- Invested in own pleural lining, separated from normal lung
  - Essentially accessory lung
Located on left in 90%, although may lie within or below diaphragm

Transpleural Systemic-Pulmonary Artery Anastomoses (Pseudosequestration)

Systemic arterial supply across pleural adhesions
Seen with pulmonary artery stenosis, less perfused upper lobes fed by intercostal arteries
Pleural arterial blush not seen with sequestration
Vessels often tangled on surface of mass

Placental Transmogrification of the Lung