An unique case of isolated right upper lobe lung agenesis with abnormal middle lobe segmentation

Isolated right upper lobe pulmonary agenesis is a highly uncommon congenital anomaly, usually detected at adulthood when the patient is evaluated for an incidental abnormal chest radiograph. Chest radiography findings are non-specific. Chest computed tomography with pulmonary angiography is the modality of choice for diagnosing pulmonary agenesis. We describe a case of isolated right upper lobe agenesis in a young man who presented with mild shortness of breath and an abnormal chest radiograph. High-resolution computed tomography chest showed right upper lobe pulmonary agenesis which was initially erroneously diagnosed as right lower lobe collapse on chest X-ray. Abnormal segmentation of the middle lobe was also seen which has not been described earlier according to our literature search. There should be a high index of suspicion for congenital anomalies on chest X-ray to recommend further imaging studies. This case highlights the importance of computed tomography with pulmonary angiography to adequately assess and characterize the congenital lung anomalies.


Background
Embryonic anomalies of the bronchi are one of the most common types of congenital malformations of the foregut. Bronchial anomalies occur in approximately 2% of the adult population, and the most common abnormality of the bronchial tree involves the right upper bronchus [1]. Pulmonary agenesis is a very rare congenital condition that represents the arrested growth of the primitive lung bud. The majority of reported cases have associated congenital anomalies involving the cardiovascular, musculoskeletal, or gastrointestinal systems. Infrequently, genitourinary or central nervous systems were involved [2]. Here, we present a case of a young man with isolated right upper lobar pulmonary agenesis and abnormal segmentation of the middle lobe.

Case presentation
Eighteen-year-old young gentleman, non-smoker, without a familial lung cancer history, presented to the respiratory clinic with mild shortness of breath. His birth history was unremarkable. There was no history of recurrent respiratory infections or bronchial asthma since childhood. There was no history of chest pain, orthopnea, palpitation, loss of appetite, or weight. His medical history was unremarkable. Physical examination showed no abnormalities. Routine blood counts and urine analysis were normal. Sputum examinations were negative for mycobacteria and bacteria. The chest radiograph showed

Open Access
The Egyptian Journal of Bronchology a mild reduction of the right lung volume with an ipsilateral shifting of the mediastinum and elevation of the right hemidiaphragm (Fig. 1). Atelectasis of right lower lobe was suspected. High-resolution computed tomography (HRCT) chest was done for further evaluation of abnormal chest radiograph. CT showed a reduction in the volume of the right lung with elevated right hemi diaphragm and mild ipsilateral mediastinal shift (Fig. 2a). The right pulmonary artery caliber was relatively smaller than the left pulmonary artery (Fig. 2b). There were bilobed bilateral lungs. The right upper lobe, bronchus, pulmonary artery, and veins of the right upper lobe were absent (Figs. 2c and 3b). Horizontal fissure was absent. A right oblique fissure was discontinuous in the right perihilar region. Superior segment of the right lower lobe was seen extending up to the apex (Fig. 3a). Two bronchi originated from the bronchus intermedius at the mid bronchus level (Fig. 3b). The first artery originating from the right main pulmonary artery was present at the level of the major fissure. Pulmonary vessels were crossing across a defect in the discontinuous oblique fissure. There was mild compensatory hyperinflation of the left lung. Left lung bronchial anatomy appeared normal. Ultrasonography of the abdomen and CT upper abdomen showed no significant anomaly in the liver, spleen, kidney, and other abdominal organs. He was diagnosed as a case of right upper lobe pulmonary agenesis.
The middle lobe showed abnormal segmentation. A right oblique fissure was seen dividing the middle lobe with the medial segmental bronchus of the middle lobe seen supplying the lung anterior to the fissure. Lateral segmental bronchus of the middle lobe and its corresponding segmental pulmonary artery was seen coursing posterior to the distal oblique fissure (Fig. 3c).
Transthoracic echocardiogram revealed no evidence of structural abnormalities. Pulmonary function tests were normal.

Discussion
Lung agenesis is a rare developmental anomaly where there is a complete absence or hypoplasia of one or both lungs. It may be present as isolated lung agenesis or may be associated with congenital anomalies [3].
Pulmonary agenesis has been classified into three types as per Boyden classification. It is morphologically  based on the extent to which bronchopulmonary tissue is absent. Type I is called pulmonary agenesis where there is a complete absence of unilateral lung parenchyma, bronchus, and its pulmonary vessels. Type II is named pulmonary aplasia where there is a complete absence of lung and its pulmonary vessels with a small rudimentary blind ending bronchus. Type III is pulmonary hypoplasia characterized by bronchial hypoplasia with variable reduction of lung tissue and its vessels [4]. The lungs normally develop from the foregut during the 4th and 5th weeks of gestation and pulmonary agenesis occurs during this period. The etiology of lung agenesis is unknown. Lack of vitamin A during pregnancy, genetic, teratogenic, and mechanical factors have been mentioned as possible causes [2,5]. The incidence of pulmonary agenesis is not exactly documented [6]. About 200 cases of unilateral pulmonary agenesis have been documented in the current literature [7]. The condition is usually unilateral. Bilateral pulmonary agenesis is incompatible with life with respiratory distress and failure. Occasionally, the agenesis may be confined to one lobe, most frequently the left upper lobe. Pulmonary artery hypoplasia is commonly accompanied with such lobar agenesis. Cases of isolated lobar agenesis have been uncommonly reported [1,3,[8][9][10].
Pulmonary agenesis may be associated with cardiovascular (tetralogy of Fallot, patent ductus arteriosus and patent foramen ovale), gastrointestinal, skeletal, and genitourinary anomalies in more than 50% of children [5]. Right lung agenesis has a relatively poor prognosis than the left side owing to complications related to mediastinal shift and more frequent association with congenital heart disease [5,7].
Isolated lobar agenesis of the lung may be asymptomatic and may go unnoticed in childhood until some complications develop. Patients may also present with dyspnea or recurrent chest infections in childhood or in adult life [2,11]. Patients are evaluated as an adult with incidental chest radiographic abnormality [11]. Chest X-ray shows loss of volume of ipsilateral hemithorax with a displacement of the mediastinal structures and diaphragm, compensatory hyperinflation, and herniation across the midline [5]. Isolated right upper lobe agenesis has been earlier reported in a few studies [1,3,12].
Chest radiograph is not diagnostic for congenital abnormalities of the lung. CT scan of the chest is the most definitive modality to diagnose such anomalies and the associated vascular anomalies. CT, magnetic resonance imaging (MRI), and CT/MR angiography are currently the imaging modalities of choice and provide important diagnostic information. Ideally, in our case, CT scan should have been combined with CT pulmonary angiography for a more confident diagnosis. CT pulmonary angiography was not done in our case as the patient did not give his consent for an intravenous contrast study. Affected lobe shows absent pulmonary parenchyma, bronchial tree, and pulmonary vessels on CT and MRI [5]. Abnormalities of the bronchi and associated vascular structures are even more clearly delineated on three-dimensional reconstruction. Patients requiring embolization or revascularization surgery may need angiography [3].
Bronchial tree pattern in our case was similar to left isomerism and hence heterotaxy syndrome has to be excluded. Left isomerism is characterized by abnormal visceral situs (midline/transverse liver, intestinal malrotation), polysplenia, congenital heart disease, azygos, or hemiazygos continuation of the inferior vena cava and bilateral bilobed lungs with the bronchial tree forming a mirror image. Our patient did not have any of these abnormalities except for bilobed lungs bilaterally. Absence of the right upper lobe, corresponding right upper lobe bronchus, and its pulmonary vessels were confirmed by CT. Anomalies in other systems were also excluded for a definitive diagnosis of right upper lobar agenesis. The middle lobe showed abnormal segmentation with medial and lateral segments of the middle lobe present medial and lateral to the discontinuous oblique fissure respectively [1]. Medical treatment is most often recommended with treatment for recurrent chest infections. Chest physiotherapy may be of some benefit. Surgical intervention is suggested in cases where there are other associated congenital anomalies. Asymptomatic cases when not associated with any other congenital anomalies do not require any treatment. The prognosis is good if there are no other malformations [2,7].

Conclusions
Congenital anomalies of the lung such as agenesis, hypoplasia, and aplasia should be considered with an abnormal chest radiograph findings mimicking collapse, in a symptomatic or an asymptomatic patient. CT with pulmonary angiography is very useful to assess and characterize the exact pathology and also its associated anomalies. Abnormal middle lobe segmentation should also be sought for, in such cases.