The details of the patient’s presentation underscore just how easily the condition can hide in plain sight. For about a week before seeking care, he had been expectorating blood-tinged sputum accompanied by a mild cough. The bleeding was intermittent and never reached massive, life-threatening volumes. Looking back, he recalled two mild respiratory tract infections during the previous year, both treated symptomatically without any formal diagnostic workup. He also described occasional mild chest pain during exertion, though it was never severe enough to limit his daily activities. He had no history of tuberculosis, asthma, chronic bronchitis, or heart disease, and his vital signs on admission were entirely within normal limits. The only physical clue was a wheeze localized to the left side of his chest on auscultation.

Contrast-enhanced computed tomography of the chest provided the answer, and it was striking. The scan showed complete absence of the left pulmonary artery, with a reduced-volume left lung being fed not by the normal arterial circuit but by an intricate network of systemic collateral vessels—alternative blood supply routes that had grown up over decades to compensate for the missing vessel. The right lung had hyperinflated to fill the gap, pushing the mediastinum slightly across the midline, a phenomenon known as mild mediastinal herniation. The left lung itself displayed smooth interlobular septal thickening and emphysematous changes, likely reflecting years of chronic hypoperfusion and post-inflammatory remodeling. Adding to the rarity of the picture, the scan revealed a right-sided aortic arch with a variant branching pattern, an associated anatomical quirk that occurs when the aortic arch develops on the opposite side from usual.

To understand how a person can be born without a major artery, one has to look at embryology. The pulmonary arteries originate from the sixth aortic arch, one of a series of paired vascular structures that remodel dramatically during early development. Between the fifth and sixth weeks of gestation, the proximal portion of the sixth arch must connect normally with the pulmonary trunk. When this connection fails, the proximal pulmonary artery never forms, while the distal intrapulmonary arterial branches may persist as small, hypoplastic vessels dependent entirely on collateral circulation. The anomaly was first described in 1868 by the German physician Fräntzel, and in the roughly century and a half since, only about 420 cases have been documented in the medical literature. In approximately 67 percent of cases, it is the right pulmonary artery that is absent; left-sided agenesis is less common and more frequently accompanied by additional cardiovascular malformations such as the right-sided aortic arch seen in this patient.

The clinical course of the condition is remarkably variable. Some patients remain completely asymptomatic throughout life, while others present in infancy with serious associated cardiac defects such as tetralogy of Fallot, ventricular septal defect, or transposition of the great vessels—cases that are typically diagnosed and surgically corrected within the first year of life. Among adults, roughly 40 percent present with exertional dyspnea, and about 20 percent develop hemoptysis or pulmonary hypertension. Other manifestations include chest pain, pleural effusion, and recurrent pulmonary infections. The bleeding that brought this patient to medical attention has a well-defined mechanistic explanation: deprived of a normal pulmonary arterial supply, the affected lung receives blood from bronchial arteries in about 70 percent of cases, and from the phrenic, intercostal, and internal thoracic arteries in roughly 40 to 50 percent each. Over time these collateral vessels hypertrophy under the abnormal workload, and their fragile, enlarged walls can rupture, producing hemoptysis that ranges from trivial to catastrophic.

Chronic hypoperfusion does more than set the stage for bleeding. The under-perfused lung becomes hypoplastic, with diminished vascularity and impaired mucociliary clearance—the conveyor-belt system of cilia and mucus that normally sweeps pathogens out of the airways. This explains the patient’s history of repeated chest infections and contributes to the emphysematous changes visible on his scan. Meanwhile, the healthy lung, forced to handle the entire cardiac output on its own, faces increased blood flow through its lone pulmonary artery, which can gradually lead to pulmonary hypertension, one of the most feared long-term complications of the condition. Transthoracic echocardiography in this patient found no evidence of elevated pulmonary artery pressures and no additional cardiac anomalies, a reassuring finding that shaped the treatment decision.

Reaching the correct diagnosis is not always straightforward, because several other conditions can produce a small lung with reduced or absent arterial flow. Hypogenetic lung syndrome, also called scimitar syndrome, features right lung hypoplasia together with an anomalous pulmonary vein draining into the systemic circulation—features absent here. Swyer–James–MacLeod syndrome, a consequence of post-infectious obliterative bronchiolitis, produces a hyperlucent, air-trapping lung rather than complete arterial absence. Chronic pulmonary embolism can shrink or occlude a pulmonary artery, but in contrast to congenital absence, the proximal vessel remains present, often showing narrowed contours, intraluminal thrombus, eccentric wall thickening, webs, bands, or calcifications. Chest radiography is usually the first test performed and can offer telling hints: a small hemithorax on the affected side, shift of the mediastinum toward it, absent hilar vasculature, diminished pulmonary markings, and compensatory hyperinflation of the opposite lung. Definitive diagnosis, however, rests on contrast-enhanced CT or MRI, which directly visualizes the missing vessel. Pulmonary angiography remains the historical gold standard but is now rarely required thanks to noninvasive imaging.

Management in this case was deliberately conservative. Because the hemoptysis was mild, the patient was hemodynamically stable, and echocardiography showed no pulmonary hypertension, his physicians opted for regular clinical follow-up with periodic echocardiography to monitor for the development of elevated pulmonary pressures. At his most recent follow-up, he remained clinically stable with no recurrence of bleeding. This measured approach is consistent with the spectrum of outcomes reported in other adults. A 67-year-old man with left-sided agenesis and massive hemoptysis was managed with observation after detailed angiographic planning, with embolization and surgery held in reserve. By contrast, a 35-year-old man and an adult woman with right-sided agenesis who developed massive hemorrhage four years after diagnosis both required pneumonectomy—surgical removal of the affected lung—the latter complicated by a bronchopleural fistula. Milder presentations have also been described, including a 24-year-old with hemoptysis and cough after a repaired ventricular septal defect, and a 55-year-old woman managed conservatively with oxygen and pulmonary vasodilators for dyspnea and hypertension.

When intervention does become necessary, the options are well characterized despite the absence of formal guidelines for adults, a gap created by the condition’s sheer rarity. Transcatheter arterial embolization is the preferred method for controlling significant hemoptysis: under fluoroscopic guidance, a catheter introduced through the femoral artery identifies the hypertrophied collateral vessels, and a microcatheter superselectively occludes the feeding vessels using polyvinyl alcohol particles, microspheres, coils, or gelatin sponge. Particles are favored for distal occlusion and coils for proximal control, though recurrence remains possible when new collateral vessels are recruited. Surgical options include lobectomy and pneumonectomy for refractory bleeding, recurrent infection, or severe hypertension, while revascularization procedures—which use autologous pericardium or synthetic materials to reconstruct the missing artery and promote lung growth—achieve better results in children than in adults. Long-term vasodilator therapy, including calcium channel blockers, phosphodiesterase-5 inhibitors, or prostacyclin analogs, can mitigate pulmonary hypertension, and combined heart-lung transplantation remains a last resort. The reported mortality rate for the condition hovers around 7 percent, driven largely by hemorrhage and pulmonary hypertension.

The broader lesson from this case is diagnostic humility. A man in his mid-fifties with an essentially clean medical history and nothing more than blood-streaked sputum turned out to be missing an entire great vessel, a structure his body had quietly routed around for decades. The authors emphasize that unexplained hemoptysis, recurrent respiratory infections, or exertional breathlessness in an adult—even one with no cardiopulmonary history—should prompt clinicians to consider congenital vascular anomalies in the differential diagnosis, with advanced cross-sectional imaging serving as the decisive tool. Early recognition allows complications such as pulmonary hypertension and catastrophic bleeding to be anticipated rather than merely reacted to, and it underscores the value of patient education about warning symptoms and the importance of lifelong surveillance. For this patient, at least, the discovery came in time: he is stable, monitored, and finally aware of the extraordinary anatomical secret he had carried since before birth.

Subject of Research: Congenital unilateral pulmonary artery agenesis with right-sided aortic arch presenting as hemoptysis in an adult

Article Title: Congenital Absence of the Left Pulmonary Artery Associated With Right‐Sided Aortic Arch Presenting as Hemoptysis in an Adult: A Case Report

Article References: Kauser, T., Khan, A., Sattar, A., Hassan, S. M. S., Raza, M., Shahab, S. H., & Habib, F. (2026). Congenital Absence of the Left Pulmonary Artery Associated With Right‐Sided Aortic Arch Presenting as Hemoptysis in an Adult: A Case Report. Clinical Case Reports, 14(9), Article e73431. https://doi.org/10.1002/ccr3.73431

Image Credits: AI Generated

DOI: 10.1002/ccr3.73431

Keywords: pulmonary artery agenesis, hemoptysis, right-sided aortic arch, congenital heart defect, contrast-enhanced CT, systemic collateral vessels, pulmonary hypertension, transcatheter arterial embolization, pneumonectomy, case report, embryology, rare disease