Comparative Study Between Anomalous Systemic Arterial Supply To The Basal Segments Of The Lung And Lung Sequestration In Adult By Computed Tomography(CT) Imaging

Background:Anomalous systemic arterial supply to the normal lung,a rare kind of congenital abnormality,receives its arterial supply from one or more of the basal segments of the lower lobe.The arterial supply coming from an aberrant artery arises from the descending thoracic aorta.Most of the researchers have claimed that the frequently involved or commonest one is the basal segment of the left lower lobe.Though it was formerly categorized as Pryce type I sequestration,the involved lung has no structural anomalies of the tracheobronchial tree that distinguish this anomaly from bronchopulmonary sequestration.It is still debatable that the word sequestration is whether relevant or not because of normal bronchial connections.Various studies have revealed that the majority of patients are asymptomatic.Lung sequestration is a rare variety of congenital anomaly met during routine high-resolution prenatal ultrasonography.It is more commonly found and is caused by an unknown aetiology.It is derived from Latin word ‘sequestare' which means ‘to separate'.It can be expressed as the segment of lung that gets its blood supply from one or more anomalous systemic arteries and does not have particular communication with the normal bronchial tree.Sequestrations are of two types intralobar and extralobar.The visceral pleural layer of an otherwise normal pulmonary lobe is seen in an intralobar sequestration whereas detachment from normal lung by its own pleural covering is seen in an extralobar sequestration.Most patients are asymptomatic and carry the abnormality for years and are only detected during a routine physical examination or if presented with recurrent bacterial pneumonia in the affected lower lobe.Symptoms are normally nonspecific,the most common symptoms of lung sequestration are cough or expectoration,fever,hemoptysis and chest pain.In case of intralobar sequestration(ILS),patients are mostly asymptomatic and accounts for nearly 75% of cases and more commonly found than extralobar sequestration(ELS).It is present almost always within the lower lobes(98% cases),more commonly on the left posterior basal segment.For diagnosis of anomalous systemic arterial supply to the normal lung,investigation modalities like computed tomography(CT),chest x-ray,magnetic resonance imaging(MRI),selective pulmonary and aortic angiography and bronchoscopy is carried out.Whereas,the basic and principal objective of imaging in every case of suspected lung sequestration should be to illustrate the aberrant vascular anatomy.So,investigations like chest x-ray,computed tomography(CT)scan,ultrasound examination,magnetic resonance imaging(MRI),conventional angiography,radionuclide angiography and barium upper gastrointestinal study are done for diagnosis of lung sequestration.However,these two diseases are very alike in nature,so from various studies following CT features are found in different patients diagnosed with these two diseases.In case of anomalous systemic arterial supply to the basal segments of the lung – it is supplied by single artery,ground glass opacity(GGO)observed in lower posterior basal segments of lung,retro cardiac nodular shadow is connected to the descending aorta branching into the basal segments of the relatively normal lower lobe,an aneurysm(50*48*43 mm)with mural calcification and partial thrombosis originating from a large,tortuous anomalous vessel,which arose from the descending aorta was found,diameter of aberrant artery from descending thoracic aorta(DTA)is increased(in some cases 25 mm,in some cases>10mm),inferior pulmonary vein is engorged/dilated and size of lung lobe is small.Likewise,in case of lung sequestration,it is supplied by three aberrant arteries,multiloculated cystic solid mass filled with low density lesions were visualized in mediastinal window,cavitary lesion,parenchymal consolidation,bronchiectasis and pneumonia is seen.Emphysematous changes observed around periphery of lung sequestration and lung lobe is normal in size.Anomalous systemic arterial supply to the basal segments of the lung and lung sequestration are both rare type of anomaly with multiple theoretical aetiologies,so often misdiagnosed due to their variable and nonspecific presentations.So,this study is proposed to confirm that CT imaging can accurately identify the arterial supply and venous drainage of the sequestered segment and help in proper diagnosis and treatment.Objective:To summarize the distinguishing variations between anomalous systemic arterial supply to the basal segments of the lung and lung sequestration in adult with the help of CT imaging features and provide basis for clinical diagnosis and subsequent treatment.Materials and Methods:This study was conducted from December 2013 to January 2019 in the radiology department,First hospital of Jilin University,Changchun,China.Medically diagnosed cases of two diseases lung sequestration and anomalous systemic arterial supply to the basal segments of the lung(n=65)were enrolled in this study.We reviewed 42 lung sequestration patients and 23 anomalous systemic arterial supply to the basal segments of the lung patients on the basis of clinical features(age,gender,symptoms like hemoptysis,exertional dyspnea,persistent dry cough)as well as CT imaging features(location of the lesion,origin of the blood vessel,vascular diameter,increased lung markings,solid or ground glass shadow,vacuoles or cavitation sign or emphysema).The chi-square test,fisher exact test and t-test were applied to compare different CT features of these two diseases.Results:In this study,a total of 65 patients diagnosed with lung sequestration(n=42)and anomalous systemic arterial supply to the basal segments of the lung(n=23)were enrolled.There was no significant statistical difference observed in the setting of the age(p=0.376)and gender(p=0.229)between both diseases.However,in regard to symptoms significant statistical differences were found with two diseases(p=0.000).Concerning the characteristics found on the basis of CT findings,there were no significant statistical differences found between these two diseases according to the location of lesion(p=0.966)and origin of blood vessel(p=0.133).Meanwhile,it was demonstrated that there were significant statistical differences on the vascular diameter(p=0.000),increased lung markings(p=0.000),solid or ground glass shadow(p=0.000)and vacuoles or cavitation sign or emphysema(p=0.000).Conclusion:As a rare variety of two different diseases of the lung including anomalous systemic arterial supply to the basal segments of the lung and lung sequestration,a multi-sliced CT imaging can accurately pinpoint the differences between them and help in providing future treatment planning.