We conducted a retrospective medical records review of all patients evaluated and treated in our institution with a pathological proven diagnosis of PS from January 2004 through December 2013. We searched the electronic medical records (EMR) using the key words: pulmonary sequestration, bronchopulmonary sequestration, extralobar and intralobar pulmonary sequestration. Reviewed EMR included office notes, surgical and interventional procedure notes, diagnostic imaging studies, and pathology reports. Our radiologists reviewed all patients’ imaging studies. We excluded patients who had imaging studies performed in outside facilities, which were unavailable for our review, and patients who had either an alternative or unproven diagnosis based on pathology reports. Collected data included demographics, clinical presentation, diagnostic imaging, location of the lesion, type of sequestration, and subsequent treatment.

Of the 29 patients, 15 were males and 14 females, 8 (28%) were children 0-2 years, 1 adolescent age 17 and 20 (69%) adults 21-70 years, with a mean age of 42.

In adults, symptoms occurred in 18 patients (90%), with the most common presentation of cough associated with recurrent pulmonary infections in 13 patients (72%), haemoptysis in 3 patients (17%), and chest pain as the primary complaint in 2 patients (11%) [Table/Fig-2].

As the majority of the adult patients presented with respiratory symptoms mimicking pneumonia and asthma, chest X-rays were performed on all patients as the first imaging modality, this often showed nonspecific pulmonary opacities such as nodules, reticular infiltrates and mass-like consolidations. On CTA, lesions suspicious for pulmonary sequestration were identified, with a systemic arterial supply to the sequestered segment demonstrated in 25 patients (86%). In 4 patients (14%), where CTA failed to demonstrate the arterial supply, two were diagnosed with angiography and the other two with magnetic resonance angiography (MRA). Furthermore, a large aberrant artery was clearly identified on CTA in all three patients who presented with haemoptysis (PPV=100%) [Table/Fig-3,4 and 5].

[Table/Fig-3]:

(a) Chest X-Ray, PA and lateral views demonstrating a right lower lobe round mass-like density (arrows), this is better visualized on the lateral view as the mass is located posterior to the heart. (b) Axial CTA chest revealing an aberrant artery branching off the descending thoracic aorta to supply a wedge shaped mass-like vascular lesion in the medial-basal segment of the right lower lobe. (c) 3D reconstructed MRA- left posterior oblique view showing the aberrant artery branching off the descending thoracic aorta, just above the diaphragm.

[Table/Fig-4]:

Axial CTA chest. A large aberrant arterial supply originating from the abdominal aorta traversing the cruciate ligament of the diaphragm and supplying a sequestered right lower lobe segment. Right image demonstrate the lung window, where an intralobar sequestration appears as a wedge shaped heterogeneous mass of cystic and nodular densities.

[Table/Fig-5]:

(a) The celiac axis gives rise to the splenic artery, left gastric and common hepatic artery. An anomalous vessel (arrow) branches off superior and medial to the proper hepatic artery. (b) Selective catheterization of the aberrant artery shows a more medial branch of this vessel extending to the diaphragmatic surface and supplies the diaphragm. (c) The artery travels laterally to supply an area of abnormal vascularity in the right costophrenic sulcus (arrow), representing the area of pulmonary sequestration, which drains into a pulmonary vein. (d) The aberrant artery was embolized using 3 coils (bottom arrow), the major supply to the pulmonary vascularity was eliminated, and the phrenic branch (top arrow) was preserved.

In 19 patients (66%), the PS was located in the left lower lobe and 16 (55%) were intralobar [Table/Fig-2].

Age, Gender and Ethnic Group Related Sequestration Type: In the adult group (21 patients) intralobar sequestrations were found in the majority of cases (81%), while in children the extralobar type was more predominant (62%). Gender distribution of sequestration types revealed a higher prevalence of extralobar sequestrations among males 54% vs. females 46%. However, intralobar sequestrations remained the most common type in both sexes, found in 53% of males and 57% of females. Of the 29 patients the Whites ethnic group formed the majority (21/29) (73%), African Americans (5/29) 17%, and Hispanics (3/29) 10%. Ethnic related variations in sequestration types may not be representative of a true genetic influenced trend of the disease as the numbers of patients in the none-white groups are too small. However, we found a significant predominance of the extralobar type among the African American group of patients (4 of the 5 patients) 80% [Table/Fig-2].

All children and symptomatic adults were treated surgically with resection of the sequestered segment (93%), and 2 of the 3 patients who initially presented with haemoptysis underwent preoperative embolization (7% of all patients). Surgical treatment was differed in two asymptomatic adults due to significant medical co-morbidities and high operative risk. These were later followed with repeated CT scans.

In 1861, Rokitansky introduced the first description of the disease, and proposed that PS occurs when pulmonary tissue separates from the lung during embryogenesis; this was later known as “the fraction theory” [6] [Table/Fig-6]. Since then, many theories were introduced to explain the possible underlying pathophysiologic mechanisms producing the malformation [Table/Fig-7] [7–15].

[Table/Fig-6]:

Principal malformations of the respiratory system at different stages during embryological development

In 1946, Pryce was the first to use the term “pulmonary sequestration”, and classified the disease into intralobar and extralobar types. An intralobar sequestration is the most common form of the disease where the lung malformation remains within the visceral pleura of its lobe, whereas the extralobar type corresponds to a true accessory lung, with a separate pleural envelope and an aberrant venous drainage [7].

As the ectopic accessory bud arise from the primitive foregut, during the fourth week of gestation, a lung-resembling structures develops without communicating with the main bronchial tree, it becomes enveloped by its separate visceral pleura and derives its arterial supply from the systemic circulation. An extralobar sequestration can be sub-classified depending on the level at which the accessory bud branches off the primitive foregut into and intrathoracic type (supradiaphragmatic), and abdominal type (subdiaphragmatic) [16].

Intralobar sequestration theories debate in defining the disease as either a congenital or acquired condition. Theories of the acquired aetiology state that chronic pulmonary infections of a lung tissue disconnected from the normal bronchial tree can cause hypertrophy of a regional systemic artery, hence the aberrant arterial supply. Despite being separated from the bronchopulmonary tree, infections may spread to the sequestered segment from adjacent aerated lung tissue via accessory inter-alveolar or broncho-alveolar connections, e.g. pores of Kohn, and canals of Lambert. These theories are supported by the low incidence of other congenital anomalies in association with intralobar sequestration, as opposed to the extralobar type [17]. Additionally, more than half of intralobar sequestrations are diagnosed in later childhood or adulthood, while the majority of extralobar types are diagnosed during infancy [18].

Previous studies have demonstrated a greater male prevalence for the extralobar sequestration, approximately 3-4 times more common in males than in females [19–22]. In our population, the extralobar type was only slightly more common in males 54% vs. females 46%. The main clinical manifestations of PS in adults are recurrent respiratory tract infections, and respiratory symptoms that often mimic other common pulmonary diseases, such as pneumonia, asthma, interstitial and obstructive pulmonary diseases [23]. In a recent study, the misdiagnosis rate of PS was reported as high as 87%, due to the wide array of nonspecific symptoms, delaying treatment and limiting therapeutic options [24].

In the largest PS case series, Yong et al., retrospectively evaluated 2625 patients from China, where the majority had presented with respiratory symptoms of cough, sputum production, fever, haemoptysis, and chest pain, while 13% of patients presented with incidental imaging findings without respiratory symptoms.

The main CT findings in this large group of patients included a mass lesions (49%), cystic lesions (29%), cavitary lesions (12%), and pneumonic lesions (8%) [25].

A comparison review of previously published series from different countries [Table/Fig-8] [6,18,25–27], demonstrates a universal male predominance of the disease among the adult population, with the majority of cases being intralobar, and more than 80% of patients typically presenting with respiratory symptoms. Surgical resection of the sequestered lesion was performed in approximately 90% of cases without significant postoperative complications.

Surgical resection remains the standard of care for all patients with PS, as it serves to establish the diagnosis, differentiate anomalous pulmonary tissue from malignancies, and prevent recurrent infectious or haemorrhagic complications [27].

Imaging techniques that can accurately identify the arterial supply and venous drainage of the sequestered segment are considered the cornerstone of preoperative planning. To prevent intraoperative morbidity and mortality caused by an aberrant vascular haemorrhage in these patients, imaging studies are applied as an essential guide for the surgical procedure.

Pulmonary angiography is thought to be the gold standard for diagnosis; however, in recent years, several studies have shown that less invasive imaging techniques such as CTA and MRA may be equally effective and safer alternatives [28–31]. In a study by Yue et al., the treatments planned with CTA showed high accuracy, and sensitivity (both >90%) in both patient and artery-based evaluations, suggesting the potential utility of CTA as the primary tool in pre-treatment planning for most PS patients [32].

In our series, CTA had a diagnostic sensitivity and specificity of 86% and 100%, respectively, and served as the primary diagnostic and preoperative planning tool.

Pulmonary sequestration is a rare disease with multiple theoretical aetiologies, often misdiagnosed due to its variable and nonspecific presentations. CTA and other imaging modalities, which can accurately identify the arterial supply and venous drainage of the sequestered segment, are essential for diagnosis and preoperative planning.