Pulmonary sequestration (PS) is a rare congenital lung malformation. It may be defined as an island of the lung that lacks a normal connection with the tracheobronchial tree and receives arterial blood supply from an aberrant branch of systemic circulation rather than the pulmonary artery. It represents 0.15–6.4% of all pulmonary malformations.1–3 Among this group of anomalies, more than 90% are found in the thorax, and less than 10% of them arise under the diaphragm.4 PSs are divided into two subgroups: intralobar pulmonary sequestration (ILS) and extralobar pulmonary sequestration (ELS).
Although numerous case reports about PS have been published in the literature, no large series on PS in adult patients from a single institution have been conducted. We retrospectively analyzed the data in this series in order to determine any significant clinical features that may affect the treatment and diagnosis of this disorder.
We retrospectively reviewed the records of patient with PS at the division of thoracic surgery in Taichung Veterans General Hospital between January 1985 and January 2011. Only patients over 16 years or older who had received surgical intervention were included. Patient consent was obtained after explaining the purpose of study and surgical procedure. Age, sex, symptoms, diagnostic methods, location of the sequestration, operative findings, surgical procedure, postoperative complications, and outcome were evaluated in all patients.
There were 31 patients (17 male and 14 female) who underwent surgical intervention for PS (Table 1). The average age was 32.1, with patients ranging in age from 17 to 57 years. Histopathologic examinations excluded other alternative diagnoses.
We observed that the major symptom was cough, and other symptoms included hemoptysis, fever, pneumonia, and chest pain or tightness. However, three patients, including two ELS patients, were asymptomatic and were diagnosed incidentally.
Chest radiography was the primary diagnostic method, and we found either patchy infiltration or mass lesion in the chest X-rays of all patients. Under the impression of PS or other malignancy, further evaluation was suggested. Thirty (96.8%) patients agreed to undergo thoracic computed tomography (CT), including computed tomographic angiography (CTA), to obtain a definitive diagnosis. For further confirmation, seven patients underwent angiography and two patients received magnetic resonance angiography (MRA).
The surgical procedures included lower lobectomy in 22 ILS patients, segmentectomy in six ILS patients, and wedge resection in one ILS patient. All except one of the resections were performed through a posterolateral thoracotomy. Video-assisted thoracoscopic surgery (VATS) was performed on one ILS patient with lobectomy and also on two ELS patients who underwent simple mass excision (Table 2).
All arterial blood supply came directly from systemic arteries, and five patients had more than one feeding artery. Venous drainage was through pulmonary veins except in one ILS patient in whom venous return was through intercostal veins. Two patients had coexistent congenital abnormalities: one ILS patient had patent ductus arteriosus and the other ELS patient had a bronchogenic cyst.
Two patients had postoperative complications: one was postoperative hemothorax and the other had prolonged air leak. However, there was no need for surgical intervention for these patients. The average duration of hospital stay was 6.4 (4–18) days, and no mortality occurred during the study.
The term “sequestration” was first introduced into the lexicon of aberrant pulmonary blood supply by Pryce in 1946.5–7 Pulmonary blood supply is usually from the systemic circulation system, such as the aorta or its branches. PS can be separated into two types: ILS and ELS. ELS, which accounts for 25% of all cases, has distinct visceral pleurae and is completely separated from the adjacent normal lung tissue. In contrast, ILS is contained within normal lung tissue without its own visceral pleurae.6–9
Numerous theories about the etiology of PS have been proposed.2,3,6–9 For ELS, the most widely accepted theory is that PS results from the persistence of systemic arteries causing traction of the lung such that a portion separates from the main lung mass.6,7 However, this cannot account for ILS. A number of authors have postulated that a systemic arterial supply may develop or be recruited as a result of lung infection, subsequently leading to the development of an ILS.2,6,7,9 Furthermore, Volpe and colleagues have suggested that a developmental abnormality with bronchopulmonary sequestration may be related to abnormal expression of the homeobox gene, Hoxb-5.9,10
Although ILS may be present in patients at any age, it tends to be diagnosed in the 1st two decades of life in approximately 50–60% of cases, but rarely before the age of 2 years.6 The age range of patients treated in this series may reflect a referral bias as our center primarily treats adult patients. In contrast to ELS, ILS is usually an isolated anomaly. In such cases, the arterial supply comes from the thoracic (73%) or abdominal (20%) aorta. Venous drainage occurs predominantly through the pulmonary venous system (more than 95%).6 In this series, 29 patients had ILS and two had ELS. One of the 29 ILS patients (3.4%) had drainage through the left intercostal veins. However, the predominant systemic venous drainage reported in the literature for ILS was via azygos, hemiazygos, or the inferior vena cava.9 In this series, the percentage of multiple aberrant arteries, 16.1%, was similar to that reported by Oliphant et al (16.0%).6,11
Cases of ELS account for approximately 25% of all PS cases.2,7,12 Most ELS cases observed in neonates can be attributed to the high frequency of coexistent congenital abnormalities (more than 60%).2,6,9,13 Congenital diaphragmatic hernia is the most common, although approximately 25% of ELS cases will have another congenital lung abnormality, such as hypoplasia, congenital cystic adenomatoid malformation, congenital lobar emphysema, or bronchogenic cyst.6 One of our patients was diagnosed to have ELS combined with bronchogenic cyst. Interestingly, most lesions coexisting with ELS and bronchogenic cyst were located at the upper thorax (or mediastinum),12,14,15 as was found in our patient. It has been well established that 80% of arterial supply comes directly from the descending aorta, 15% from another systemic artery, and 5% from the pulmonary artery. Moreover, 80% of patient venous drainage is into the systemic circulation.6
In this series, the percentage of asymptomatic patients was 9.7%. Savic and colleagues reported that 15% of patients with PS had no symptoms when diagnosed.16,17 However, the comparable percentage was higher in studies reported by Petersen et al7 and Hirai et al.16 The difference may be attributed to the unpopular concept of regular checkups, and the fact that chest radiographs would not normally be taken until there were persistent symptoms. Owing to the potentially severe complications of the disease, surgical resection is suggested whenever PS is diagnosed.2,4
Traditionally, conventional angiography is the gold standard for the definitive diagnosis of PS and for demonstrating arterial supply and venous drainage,10,18 despite the invasiveness of this method. According to the report of Lai and colleagues, 19 the preoperative diagnostic rate with conventional angiography was satisfactory, but the utility rate of CT scan was quite low. In recent years, both MRA and three-dimensional CT scan reconstructions have been used to delineate the vascular anatomy of sequestrations.9,20 Lee et al21 demonstrated that multidetector CT angiography is capable of displaying the arterial and venous vascular anatomy of PS. The earliest patient in our dataset was admitted in January 1985. With regard to the imaging modality used to obtain a definitive diagnosis, 30 patients underwent thoracic CT, including CTA, two patients received both CT and MRA, and one patient accepted MRA only. Before 2000, seven of 12 patients who received CT scan required aortography for further confirmation. Since 2000, definitive diagnosis and delineation of the aberrant arteries was achieved through CT scan only (Fig. 1) in 17 of 18 patients, but two still received MRA (Fig. 2). The only patient who could not be diagnosed preoperatively was the patient with coexisting ELS and bronchogenic cyst. Although the sensitivity and specificity of diagnosis could not be evaluated accurately, the diagnosis rate in our series was as high as 94.4%. Arising from the improvement of diagnostic techniques and experience, we believe that patients in whom a diagnosis of PS is highly suspected on chest radiography can be diagnosed definitively through a noninvasive procedure, such as CTA or MRA.
Owing to its multiplanar capability, magnetic resonance imaging (MRI) can also depict systemic arterial anatomies, pulmonary venous return, and the relationship of the draining vein to the cardiac chamber. Multidetector CT angiography has the advantage of being able to show a pulmonary parenchymal abnormality as well as the arterial and venous anatomy.22,23 Furthermore, CT scan times are significantly shorter than those of MRI. The advantage of MRI over CT is the absence of radiation risks. However, the need for prolonged sedation time in children undergoing MRI as well as the suboptimal capability of this modality for evaluation of lung parenchymal abnormalities must be taken into consideration.22 In this series, all but one patient were diagnosed with PS by CT scan after 2000. We highly recommend CT angiography for diagnosis in patients with an elevated suspicion of PS.
One of the most difficult aspects of performing a resection of a PS is identifying the anomalous vasculature. Preoperative delineation of the aberrant artery can facilitate operative management and reduce the occurrence of fatal outcomes. The surgical sequence should also be strictly adhered to. For PS, aberrant arteries need to be occluded first. If the pulmonary vein is occluded first, lung parenchyma would rapidly become congested because of the systemic blood inflow. Then, oozing from the rough surface of the sequestrated lung would deteriorate. Hence, no intrapulmonary vessels should be sacrificed before PS can be confirmed and the aberrant vessels identified. In our series, three patients had blood loss of more than 1000 ml during operation. In one case, blood loss was attributable to the opposite sequence of vessel ligation, and the others were simply attributed to severe adhesion. Gezer et al2 stated that preoperative identification of the aberrant vessels is not an absolute requirement for the operative success of PS, but we still strongly recommend preoperative localization of the aberrant vessels to avoid major bleeding in the operation. Although ILS lacks its own visceral pleurae and is contained within normal lung tissue, we still could identify the margin from sequestration to normal lung tissue. Hence, we could perform wedge resection along this margin. However, basal segmentectomy or lobectomy should be considered if most of the pulmonary parenchyma were involved.
In this series, three patients received thoracoscopic surgery: two had ELS and the other had ILS. The importance of VATS is that it allows for identification of the aberrant arteries (Fig. 3). It would be more difficult to perform proper identification if there were inflammatory changes due to recurrent pulmonary infection. Because of our limited experience and the small number of operations, it is not possible to meaningfully compare differences between VATS and the open approach. Kestenholz and colleagues1,24 noted that thoracoscopic treatment of PS is feasible and can be performed safely. However, they did experience a considerable learning curve.
In conclusion, surgical resection for PS is recommended because of the potential complications associated with this disorder. Noninvasive diagnostic imaging modalities such as CTA or MRA are valuable for obtaining a definitive diagnosis. CTA may be the diagnostic imaging method of choice for optimal evaluation of the sequestrated lung and its vascular supply. Preoperative identification of the aberrant vessels of PS is necessary to avoid severe complications. If there is no severe adhesion, VATS is an alternative choice for the treatment of PS.
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