Diagnostic Puzzlers: A patient with an "extra" pulmonary blood vessel

A 79-year-old woman with a history of atrial fibrillation was referred to the pulmonary service for preoperative evaluation for hip replacement surgery. She reported that 20 or more years ago she had been told by her physician that she has an "extra blood vessel" in the right lung. It had not caused her any difficulty. Her medical history was also notable for a heart murmur and gastroesophageal reflux disease secondary to a large hiatal hernia. She was a nonsmoker.

The patient had decreased ambulation as a result of hip pain. She had no complaints of orthopnea, paroxysmal nocturnal dyspnea, chest pain, or cough. On chest examination, she had good air entry bilaterally, with clear lung fields. Her cardiac examination was notable for an irregular rhythm, with a loud, blowing systolic murmur heard over the right upper sternal border radiating to the neck and left sternal border.

The patient's CT scan of the chest is shown (Figure 1A, lung window view; Figure 1B, mediastinal view).

What is the likely diagnosis? Can she proceed to surgery?

A patient with an "extra" pulmonary blood vessel: The CT scan of the chest reveals a large right-sided pulmonary vein that does not return to the main pulmonary artery; instead, it empties into the inferior vena cava (IVC). This is known as a scimitar sign.A contrast-filled collection in the center of the CT scan is evidence of a large hiatal hernia.

Discussion

The scimitar sign is the crescentic shadow seen on a chest radiograph or CT scan. Although Halasz and colleagues¹ introduced the term "scimitar" in 1956 (based on its similarity in appearance to the Turkish sword), this type of pulmonary venous drainage was first described in 1836, when Chassinat and Cooper independently reported separate cases.^2-4

The scimitar vein accounts for about 0.5% to 1% of cases of congenital heart disease. It is a congenital defect that involves anomalous pulmonary venous drainage of the right lung into the IVC or drainage of the pulmonary vein into the hepatic or portal vein⁵; the drainage may involve a portion of the venous return from the right pulmonary circulation or drainage from the entire right side.

The oxygen-carrying scimitar vein usually connects to the IVC below the diaphragm or at the junction of the IVC with the right atrium; it also can be associated with atrial septal defects. A left-to-right shunt may occur in association with right ventricular failure secondary to long-standing volume overload.⁶ There have been reports of left-sided scimitars and bilateral scimitars.^7,8

The scimitar sign should be distinguished from scimitar syndrome, first coined by Neill and associates^6,9 in 1960.This syndrome involves anomalous pulmonary venous return in association with a hypoplastic right lung and a systemic blood supply to the right lung. It occurs in about 3% to 5% of scimitar cases. The evaluation of a patient with scimitar syndrome involves transthoracic and transesophageal echocardiography and heart catheterization with determination of pulmonary-to-systemic blood flow (Q_p:Q_s) ratio.

Scimitar syndrome is also associated with other congenital heart anomalies, including tetralogy of Fallot, dextroposition of the heart, patent ductus arteriosus, ventral septal defects, and patent foramen ovale; therefore, a thorough evaluation for these defects is essential. Scimitar syndrome can also be associated with pulmonary sequestration or horseshoe lung.

Surgical correction for a scimitar sign or scimitar syndrome is usually undertaken for symptomatic patients or asymptomatic patients with a Q_p:Q_s ratio greater than 1.5:1. Higher Q_p:Q_s ratios are associated with a higher incidence of pulmonary hypertension and right ventricular failure.^6,10,11 The type of surgical repair that is performed depends on multiple factors, including whether the pulmonary arterial circulation originates in the systemic or pulmonary circulation; whether pulmonary sequestration is present; and whether there are other defects, such as septal defects.

Surgical techniques include the creation of a tract and an atrial septal defect, known as an intra-atrial baffle; this technique connects the scimitar vein into the left atria while the patient is on cardiopulmonary bypass or directly implants the scimitar vein into the left atrium without the use of cardiopulmonary bypass.^12,13If pulmonary sequestration or horseshoe lung is present, lung resection may be necessary.¹² Asymptomatic patients with a low Q_p:Q_s ratio may be observed.

Outcome in this case

Before hip surgery, the patient had a cardiology evaluation. The echocardiogram was notable for normal left ventricular systolic function and a mildly dilated left atrium; the mitral inflow pattern was consistent with diastolic dysfunction. There was no evidence of a septal defect, shunt, or pulmonary hypertension. She proceeded with the hip replacement surgery without incident.

Case and photographs courtesy of Paul Strachan, MD, Shraddha Tongia, MD, Rubin Cohen, MD, and Arunabh Talwar, MD, of Long Island Jewish Medical Center, New Hyde Park, New York, and North Shore University Hospital, Manhasset, New York.

References:

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