Comparison of anomalous systemic artery to left lower lobe and pulmonary sequestration in left lower lobe by computed tomography

Abstract

Background

Differentiation of anomalous systemic artery to the left lower lobe (ASALLL) from pulmonary sequestration (PS) is essential, as ASALLL can be corrected by anastomosis, embolization, or ligation of the anomalous artery.

Purpose

To compare computed tomography (CT) findings of ASALLL and PS in the left lower lobe (LLL).

Materials and methods

This study included 16 patients with ASALLL and 25 patients with PS in LLL confirmed by operative and pathologic findings.

Results

Cough and sputum were more common in PS (84% and 60%, respectively) than in ASALLL (25% and 12.5%, respectively) (P < 0.05). Hemoptysis was more common in ASALLL (100%) than in PS (24%) (P < 0.05). The frequency of ground glass opacity (GGO), normal bronchial distribution, dilated left inferior pulmonary veins, and absence of the interlobar artery distal to the origin of the superior segmental artery in LLL differed significantly between ASALLL and PS. Mass was less common in ASALLL (0%) than in PS (88%) (P < 0.01). The mean diameter of the anomalous artery (11.88 ± 1.13 mm) in ASALLL was significantly larger than that (5.96 ± 0.98 mm) in PS (P < 0.01). The presence of anomalous artery arising from thoracic aorta was not different between ASALLL (100%) and PS (72%).

Conclusion

Radiographic indications of ASALLL differ from those of PS in the LLL. Indications that may suggest ASALLL include an enlarged anomalous systemic artery arising from the thoracic aorta, dilated left inferior pulmonary veins, absence of the interlobar artery distal to the origin of the superior segmental artery, normal bronchial distribution, and GGO in the LLL.

Keywords

Anomalous systemic artery sequestration computed tomography (CT)X-ray

Introduction

Anomalous systemic artery to the left lower lobe (ASALLL), which has no normal pulmonary arterial supply (LLL), is a congenital anomaly that does not affect bronchial connections (1). ASALLL was previously classified as a type I pulmonary sequestration (PS) according to Pryce’s terminology (2). Whether the term “sequestration” is appropriate remains controversial because bronchial connections remain intact (3 –5). PS, however, is an anomaly in which an anomalous systemic artery disrupts communication of the pulmonary tissue with the tracheobronchial tree (5). In most cases of ASALLL and PS, lobectomy or segmentectomy can be performed (1,3), while other operative procedures such as anastomosis between the anomalous artery and the pulmonary artery, embolization, or ligation of the anomalous artery, can be performed only in patients with ASALLL (1,3,6 –8). Therefore, it is very important to differentiate ASALLL from PS. To our knowledge, little information is available on the CT features that may distinguish ASALLL from PS. In this study, we compared the CT findings of 16 patients with ASALLL and 25 patients with PS in LLL confirmed by operative and pathologic findings.

Material and Methods

Patients

This study included 41 patients admitted to our hospital for surgery, including 16 patients with ASALLL (11 men, 5 women; mean age 23 ± 5 years) and 25 patients with PS (15 men, 10 women; mean age 27 ± 7 years). Patients were selected from a population of 857 who underwent lobectomy or segmentectomy in our institution from January 2005 to August 2013 by a review of medical records. Of these 857 patients, lobectomy or segmentectomy of the left lower lobe was performed in 435, and of these those, 16 and 25 patients were diagnosed with either ASALLL or PS, respectively. All patients’ symptoms completely resolved after surgery. No mortality was encountered.

CT scanning

Chest CT images were obtained with a 320-detector CT scanner (Aquilion ONE; Toshiba Medical Systems, Ottawara, Japan) (n = 29) or a HiSpeed Advantage scanner (GE Healthcare, Milwaukee, WI, USA) (n = 12). Scan parameters were as follows: 120 kV, 160–250 mAs. The reconstructed slice thickness and interslice interval were 3 mm. Routine chest CT images were obtained from the apex to the base of the lung and were viewed using standard lung (level, −700 HU; width, 1500 HU) and mediastinal windows (level, 40 HU; width, 400 HU). Iodinated non-ionic contrast medium (Iopromide; 300 mg/mL; Schering Pharmaceutical Ltd., Guangzhou, China) was administered at a rate of 2.5 mL/s with a mechanical injector. Multi-planar curve reconstructions (MCR), maximum intensity projections (MIP), and three-dimensional (3D) volume rendered images were generated.

Data analysis

Chest CT images and clinical findings were analyzed by consensus by two experienced radiologists (JQ and MJB, who have 15 and 10 years of experience in chest imaging, respectively) individually. Chest pain, cough, sputum, fever, and hemoptysis were evaluated in all patients. CT images were assessed for the following patterns of abnormality: GGO or mass, bronchial distribution, dilated left inferior pulmonary veins, absence of the interlobar artery distal to the origin of the superior segmental artery, and the origin and mean diameter of the anomalous artery. The diameter of the anomalous artery was measured at its origin.

Statistical analysis

All statistical analyses were performed using the Statistical Package for the Social Sciences software package version 20.0 (SPSS Inc., Chicago, IL, USA). Continuous data were expressed as the means with standard deviations (SD) and categorical data as numbers with related percentages (n, %). Differences in continuous data were analyzed using Student’s t-test, and categorical data were compared using the chi-square test. A two-tailed P value <0.05 was considered to indicate statistical significance.

Results

Clinical findings

Cough and sputum were more common in PS (84% and 60%, respectively) than in ASALLL (25% and 12.5%, respectively) (P < 0.05). Hemoptysis was found in 16 (100%) cases of ASALLL and six (24%) cases of PS (P < 0.05). Chest pain, fever, and lack of symptoms occurred at equal frequencies among patients with each lung abnormality (Table 1).

Table 1.

Clinical findings of ASALLL and PS in LLL.

	Chest pain	Cough	Sputum	Fever	Hemoptysis	No symptoms
ASALLL (n = 16)	0 (0)	4 (25)	2 (12.5)	0 (0)	16 (100)	0 (0)
PS (n = 25)	2 (8)	21 (84)	15 (60)	8 (32)	6 (24)	3 (12)
P	1.00	<0.01	0.04	0.15	<0.01	0.56

Data are numbers of patients, and data in parentheses are percentages.

CT findings

The frequencies of ground glass opacity (GGO), normal bronchial distribution, dilated left inferior pulmonary veins, and absence of the interlobar artery distal to the origin of the superior segmental artery in LLL differed significantly between ASALLL and PS (Figs. 1 –4). Masses were less commonly observed in ASALLL (0%) than in PS (88%) (P < 0.01, Fig. 3). The mean diameter of the anomalous artery (11.88 ± 1.13 mm) in ASALLL was significantly larger than that in PS (5.96 ± 0.98 mm) (P < 0.01, Fig. 4). The frequency at which anomalous arteries arose from the thoracic aorta did not differ between ASALLL (100%) and PS (72%) (Table 2).

Fig. 1.

A 35-year-old man with ASALLL presented hemoptysis. (a) Sequential axial CT images in LLL show an anomalous systemic artery (ASA) originating from the lower descending thoracic aorta is 13 mm in diameter. (b) Sequential axial CT images at the lung window setting in LLL show normal bronchial distribution, GGO, and dilated left inferior pulmonary veins in LLL. (c) MIP and (d) VR show ASA arising from lateral aspect of thoracic aorta to LLL and dilated left inferior pulmonary veins. The interlobar artery distal to the origin of the superior segmental artery is absent. No direct communications exist between the anomalous systemic artery and the veins of the basal segments.

Fig. 2.

A 29-year-old man with PS (intralobar). (a) Lung window setting shows an intrapulmonary ill-defined mass with solid and cystic components in the LLL without dilated left inferior pulmonary veins. The mass of abnormal pulmonary tissue does not communicate with the tracheobronchial tree. (b) MCR shows ASA arising from lateral aspect of thoracic aorta is 7 mm in diameter.

Fig. 3.

A 39-year-old woman with PS (extralobar). (a) Mediastinal window setting shows a well-defined solid mass with solid and cystic components in the LLL. (b) Mediastinal window setting shows ASA arising from lateral aspect of thoracic aorta is 5 mm in diameter.

Fig. 4.

The mean diameter of anomalous artery in ASALLL was significantly larger than that in PS (P < 0.01).

Table 2.

CT features of ASALLL and PS in LLL.

					Pattern of anomaly
	Normal bronchial distribution	Absence of the interlobar artery	Anomalous artery arising from thoracic aorta	Dilated left inferior pulmonary veins	GGO	Mass
ASALLL (n = 16)	16 (100)	16 (100)	16 (100)	16 (100)	16 (100)	0 (0)
PS (n = 25)	0 (0)	0 (0)	17 (68)	0 (0)	0 (0)	22 (88)
P	<0.01	<0.01	0.15	<0.01	<0.01	<0.01

Data are numbers of patients except diameter, and data in parentheses are percentages.

Discussion

Whether ASALLL differs from classic PS has long been debated (6 –8). PS is a mass of abnormal pulmonary tissue supplied by an anomalous systemic artery that does not communicate with the tracheobronchial tree (3 –5). ASALLL, therefore, cannot be considered a true type of PS, because it is defined by a normal bronchial distribution in the affected segments. In the present study, we found that normal distribution in the LLL was more common in ASALLL than in PS (P < 0.01), confirming that bronchial distribution in ASALLL differs from that in PS.

Yamanaka et al. reported that anomalous arteries in ASALLL are of small diameter (mean, 9 mm) in the pulmonary ligament at its origin, but are aneurysmatically dilated (mean, 20 mm in diameter) just beyond the site entering the lobe (8). Yue et al. reported a similarly small mean diameter of the aberrant arteries in PS, 6.3–6.6 mm (3). Our results are similar to these previous reports. To our knowledge, few studies have compared anomalous artery diameter in the two conditions (4 –9). The present study found that anomalous arteries in ASALLL are significantly larger (mean diameter, 11.88 ± 1.13 mm) than in PS (5.96 ± 0.98 mm) (P < 0.01). The mean diameter of the anomalous artery may therefore be helpful in distinguishing ASALLL from PS.

In our study, GGO was more common in ASALLL than in PS. GGO in these cases usually resulted from an increase in blood due to the large anomalous artery, which may also cause hemoptysis and dilated left inferior pulmonary veins. Another potential contributor to GGO in ASALLL is intra-alveolar hemorrhage. Recurrent hemoptysis is reason to suspect ASALLL in young adults (10,11).

Several studies have shown that the interlobar artery distal to the origin of the superior segmental artery is absent in ASALLL (10 –14). In PS, however, normal pulmonary arteries are present in the left lower lobe (11,12). The absence of the interlobar artery distal to the origin of the superior segmental artery in the LLL may thus be a distinguishing feature of ASALLL (11 –15).

ASALLL differs from pulmonary arteriovenous malformations (PAVM). PAVM consists of an abnormal direct communication between the pulmonary arteries and pulmonary veins without interposition of a capillary bed, while there is a capillary bed between the pulmonary arteries and pulmonary veins in ASALLL (16). Contrast-enhanced CT scanning can accurately, non-invasively diagnose ASALLL and PAVM (16,17). A venous sac, tortuous feeding arteries, and a dilated drainage vein are the characteristic CT findings of PAVM (16,17).

Our study had several limitations. First, this was a retrospective study including a relatively small number of patients. Second, we believe that some cases of ASALLL were excluded in our hospital, because of an inability to definitively diagnose the condition. Finally, we did not compare ASALLL to intralobar or extralobar sequestration.

In conclusion, on CT, ASALLL is characterized by an enlarged anomalous systemic artery arising from the thoracic aorta, dilated left inferior pulmonary veins, absence of the interlobar artery distal to the origin of the superior segmental artery, normal bronchial distribution, and GGO in the LLL. In contrast, PS typically presents as a mass-like lesion with a round or pyramidal shape supplied by a smaller anomalous artery, frequently containing cystic spaces (air-fluid levels). Recognition of these CT findings may be helpful in differentiating ASALLL from PS.

Footnotes

Conflict of interest

None declared.

Funding

This work was supported by the National Natural Science Foundation of China (81101096) and the Medical Scientific Research Foundation of Guangdong Province (B2011102).

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