Lung pseudosequestration: Anomalous systemic arterial supply to normal right lower lobe

A 47-year-old female patient presented with bronchospasm for the last 14 days as chief complaint. Previous medical history was otherwise irrelevant. As part of her medical work up, a chest CT was requested and upon findings a thoracoabdominal CT angiography (CTA) was ordered.

Chest CT displayed no signs of bronchopulmonary disorders but showed an abnormal vascular structure coursing through the basal segments of the right lower lobe along with regional subtle ground-glass opacities. This finding had an apparent infradiaphragmatic origin (Fig. 1). No other structural alteration of the lung parenchyma or tracheobronchial tree was found. A thoracoabdominal CTA confirmed the previous finding and revealed its origin in the coeliac trunk (Fig. 2,3). An anomalous systemic arterial supply to the normal right lower lobe (with normal pulmonary artery; dual supply) was diagnosed.

A multidisciplinary team meeting was adjourned to discuss possible treatments. While no consensus was reached regarding the optimal treatment alternative, the patient opted for strict clinical follow up. The patient's chief complaint faded days after the initial CT scan. A year has passed since the diagnosis was made, and the patient still remains asymptomatic.

Anomalous systemic arterial supply to the lung with normal tracheobronchial development is a rare condition. Sade et al introduced the concept of a “sequestration spectrum” to classify a wide range of bronchovascular anomalies. Clemens and Warner also presented a similar spectrum notion term “pulmonary malinosculation” [1,2]. Since the bronchopulmonary tree and the lung parenchyma are normal, the term pseudosequestration has been proposed. As seen in the present case, this combination is the rarest, as it most commonly affects the left lower lung and the aberrant artery emerges from the lower thoracic aorta. On the contrary, when the right lower lung is affected, the anomalous artery often arises from the coeliac trunk or abdominal aorta [1-3]. There are two subtypes: isolated systemic arterial supply to normal lung and systemic arterial supply associated with normal pulmonary artery (dual supply). The origin of this condition is believed to be an abnormal embryogenesis due to a lack of regression of the primitive aortic branches to the developing lung bud [4].

Traditionally, the anomalous systemic artery accesses the lung through the pulmonary hilum or the pulmonary ligament. Additionally, ground-glass opacities or some lung volume loss can be observed [5]. It has been stated that ground-glass opacities can be caused by intra-alveolar haemorrhage [6].

Most adult patients who suffer from lung pseudosequestration are asymptomatic and the main form of presentation is an incidental finding in imaging studies. Symptoms include cough, hemoptysis, dyspnea, or congestive cardiac failure due to left-sided volume overload secondary to left-to-left shunt later in life [1-7]. In the pediatric population, a typical exhibiting symptom is a cardiac murmur [8].

CT and CTA are non-invasive techniques used for a definitive diagnosis. Multidetector CT can demonstrate the origin, the course of the aberrant artery, and the architecture of the bronchopulmonary tree including the lung configuration. Multiplanar reformation and 3D volumetric imaging play an important role in pretreatment planning. Plain radiography and MRI play a secondary role in reaching the definitive diagnosis. An effort should be made to correctly individualize and name the bronchovascular components of these anomalies and their interrelationship rather than encasing the findings under a proper medical label. Conventional angiography still remains a vital tool in endovascular management. Treatment strategies include lobectomy or segmentectomy, with ligation or anastomosis of the abnormal systemic artery, or endovascular embolization if there is a dual arterial supply to the lung [1-8].