Ann Thorac Surg 2004;77:1085-1087
© 2004 The Society of Thoracic Surgeons
Case report
Horseshoe lung with left lung hypoplasia and critical pulmonary venous stenosis
Joel Lutterman, MDa,
Roy Jedeikin, MDa,
David C. Cleveland, MDb*
a Arizona Pediatric Cardiology Consultants, PC, Phoenix, Arizona, USA
b Children's Health Center, Division of Cardiothoracic Surgery, St. Joseph's Hospital and Medical Center, Phoenix, Arizona, USA
Accepted for publication May 8, 2003.
* Address reprint requests to Dr Cleveland, 500 West Thomas Rd, Suite 680, Phoenix, AZ 85013, USA
e-mail: dclevel{at}chw.edu
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Abstract
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Horseshoe lung is a rare congenital anomaly characterized by an isthmus of the pulmonary parenchyma that extends posterior to the pericardial reflection at the cardiac apex and across the midline. There is unilateral, usually right-lung hypoplasia and most cases are associated with the scimitar syndrome. We present the case of an infant with horseshoe lung but with hypoplasia of the left lung and levocardia that was not associated with the scimitar syndrome.
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Introduction
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Horseshoe lung, first described in 1962, remains a rare clinical finding [1]. Approximately 40 cases have been reported in the world literature [2], almost all of which have been associated with the scimitar syndrome [3]. Patients with the scimitar syndrome present with variable hypoplasia of the right lung in which the "horseshoe" is formed from the joining of the base of the right and left lungs by an isthmus of lung parenchyma that is posterior to the heart. Infants presenting with horseshoe lung and scimitar syndrome usually have severe cardiorespiratory distress. Invariably, these infants have systemic-to-suprasystemic pulmonary artery pressures that contribute to a poor prognosis.
A 2.6-kg neonate presented with a 3-day history of increasing respiratory distress. The clinical exam demonstrated a phenotypically normal, small, and frail-appearing infant with significant respiratory distress and tachycardia. The echocardiogram revealed normal intracardiac anatomy with a prominent right ventricular cavity, severely hypoplastic branch pulmonary arteries, very hypoplastic pulmonary veins with a small confluence to the left atrium, critical stenosis of the pulmonary venous connection to the left atrium, and a calculated suprasystemic right ventricular pressure.
Because of the unusual nature of the pulmonary arterial and venous anatomy, the patient underwent cardiac catheterization with angiography, which demonstrated diffusely hypoplastic and bizarrely branching pulmonary arteries (1.5 to 2.0 mm), with the left supplying a posterior midline lung (Fig 1A). All the left pulmonary veins and the right lower pulmonary vein drained to a small confluence posterior to the left atrium. The right upper pulmonary vein appeared to drain normally. The confluence had a critically stenotic connection to the medial portion of the left atrium (Fig 1B).
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Fig 1. (A) Pulmonary angiogram demonstrates the midline course of a very hypoplastic left pulmonary artery. It arborizes to both the very hypoplastic left lung, which includes the isthmus that creates the horseshoe lung. (B) The levophase demonstrates the very abnormal pulmonary venous return from the left and right lung. The pulmonary veins enter the left atrium through a 1 mm orifice next to the atrial septum.
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The patient was referred for operative correction of the pulmonary venous stenosis. At operation, the patient was noted to have a markedly enlarged right ventricle, the noticeable lack of lung tissue anteriorly, and what appeared to be a midline posterior connection of the right and left lung. The pulmonary arterial tree was very hypoplastic and abnormal: no true left pulmonary artery was noted, but a hypoplastic branch from the right pulmonary artery going to posterior midline lung tissue was seen. A critically stenotic (admitted a 1-mm probe) connection of hypoplastic pulmonary venous confluence to the left atrium was seen. The confluence was opened widely, and the connection to the left atrium was enlarged.
Postoperative echocardiography revealed a widely patent connection of the pulmonary veins to the left atrium. Pulmonary artery pressures were monitored for 72 hours postoperatively with documented persistent pulmonary hypertension to near systemic levels. Because of the unusual appearance of the lungs at operation and the concern about lung hypoplasia, a computed tomographic (CT) scan was obtained (Fig 2). This clearly demonstrated the horseshoe lung with fusion of the posterobasal portions of the right and left lungs behind the pericardial reflection.
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Fig 2. Computed tomographic scan demonstrates a very hypoplastic left lung with a midline isthmus extending across the midline that creates the horseshoe lung.
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The patient was gradually weaned off all inotropic agents but could not be extubated. On the 19th postoperative day, the patient suffered a cardiopulmonary arrest that seemed to be associated with sepsis and could not be resuscitated. The family declined an autopsy.
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Comment
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Horseshoe lung is a rare anomaly that should be included in the differential diagnosis in patients presenting with unilateral lung hypoplasia. A review of the English language literature reveals that all cases except for that of a 20-week fetus [4] and that of a 2
-year-old girl [5] are associated with right lung hypoplasia and variations in pulmonary venous drainage, with most patients concurrently presenting with the scimitar syndrome. Although Dupuis and colleagues [3] and Frank and colleagues [6] described horseshoe lung in terms of right lung hypoplasia, the operative findings and CT scan in our patient clearly demonstrate the fusion of posterior-inferior lung segments behind the heart and anterior to the aorta. In this case, however, there was no cardiac dextrorotation or dextroversion and no apparent right lung hypoplasia. The left lung was, however, hypoplastic and the pulmonary venous drainage from this lung was very abnormal. It seems to us that a better characterization of horseshoe lung would be that proposed by Hawass and colleagues [7], with horseshoe lung being "characterized by the presence of unilateral pulmonary hypoplasia and a midline isthmus." They also observe that the isthmus originates from the hypoplastic lung in all reported cases.
The etiology of horseshoe lung remains speculative at the present time. What does appear to be clear is that whatever disturbance in organogenesis that initiates the development of horseshoe lung may also result in abnormal pulmonary venous return. It is tempting to propose an arrest in development of the lung tissue differentiation early in embryogenesis. This would be compatible with our observations of pulmonary arterial, venous, bronchial, and parenchymal hypoplasia.
Patients with horseshoe lung and the infantile form of scimitar syndrome almost always have deficient lung tissue, which contributes to the high mortality rate associated with the disease. Our patient had a very unusual variant of anomalous pulmonary venous connection and what appeared to be an embryologic arrest in pulmonary artery development.
In this patient, my colleagues and I observed the constellation of a horseshoe lung with left lung hypoplasia and critical pulmonary venous stenosis that was not associated with the scimitar syndrome. The pathophysiology appears to be similar to horseshoe lung with scimitar syndrome and is probably also associated with variable degrees of pulmonary hypertension and an overall poor prognosis.
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References
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- Spencer H. Pathology of the lung. , 3rd ed Oxford: Pergamon Press, 1977.
- Männer J., Jakob C., Steding G., Füzesi L. Horseshoe lung: report on a new variant—"inverted" horseshoe lung—with embryological reflections on the formal pathogenesis of horseshoe lungs. Ann Anat 2001;183:261-265.[Medline]
- Dupuis C., Rémy J., Rémy-Jardin M., Coulomb M., Breviére G.M., Ben Laden S. The "horseshoe" lung: six new cases. Pediatr Pulmonol 1994;17:124-130.[Medline]
- Hawass N.D., Badawi M.G., Meshari A.A., Edrees Y.B. Horseshoe lung with multiple congenital anomalies. Case report and review of the literature. Acta Radiol 1987;28:751-754.[Medline]
- Ersoz A., Soncul H., Gokgoz L., et al. Horseshoe lung with left lung hypoplasia. Thorax 1992;47:205-206.[Abstract/Free Full Text]
- Frank J.L., Poole C.A., Rosas G. Horseshoe lung: clinical, pathologic, and radiologic features and a new plain film finding. AJR Am J Roentgenol 1986;146(2):217-226.[Abstract/Free Full Text]
- Hawass N.D., Badawi M.G., Al-Muzrakchi A.M., et al. Horseshoe lung: differential diagnosis. Pediatr Radiol 1990;20:580-584.[Medline]
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Abstract
Introduction
