Anterior Subtype of Partial Anomalous Left Pulmonary Artery

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An 82-year-old female patient recently diagnosed with polymetastatic breast cancer was referred to the emergency department for sudden shortness of breath and underwent CT pulmonary artery angiography. CT images incidentally showed a small accessory left pulmonary artery arising off the inferior aspect of the right pulmonary artery, coursing anterior to the airways to the left lung, supplying the lingula. The proper left pulmonary artery supplied the remaining left upper and lower lobes (Figs 1, 2; Movie).

Figure 1:

(A–D) Contrast-enhanced pulmonary artery angiographic images in an 82-year-old female patient with anterior partial anomalous left pulmonary artery (PALPA). (A) Axial CT image shows relationship of the left atrial appendage (laa) and left superior pulmonary vein (lspv) to the PALPA (*). (B) Sagittal CT reformatted image shows the relationship of the PALPA (*) along the anteroinferior aspect of the left main bronchus (LM) and anterior to the esophagus (e). (C, D) Coronal CT reformatted images show the origin of PALPA (*) from the inferior aspect of the right pulmonary artery (RPA), coursing inferior to the LM. LPA = left pulmonary artery, MPA = main pulmonary artery, RM = right main bronchus.

Figure 2:

Three-dimensional CT reconstruction of anterior partial anomalous left pulmonary artery (PALPA). (A) Coronal view and (B) cranial view. * = PALPA. LPA = left pulmonary artery, MPA = main pulmonary artery, RPA = right pulmonary artery.

Movie:

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Multimedia for axial CT images of the CT pulmonary artery angiography.

No associated pulmonary venous, tracheobronchial, or cardiac anomaly was observed.

Partial anomalous left pulmonary artery (PALPA) is a rare congenital vascular variant (1–5) thought to be related to developmental defects of the sixth aortic arch (1). It is characterized by an accessory arterial branch arising from the right pulmonary artery supplying a portion of the left lung.

The various associated anomalies with PALPA include congenital heart disease and airway malformations. Associated noncardiopulmonary malformations include skeletal, gastrointestinal, and genitourinary anomalies, as well as Kabuki syndrome (1). Although PALPA can coexist with multiple congenital abnormalities, it can also be detected incidentally and in isolation, as in this case.

PALPAs can be classified into anterior and posterior subtypes based on their relationship to the tracheobronchial tree. In the anterior subtype, the aberrant artery courses anterior to the tracheobronchial tree, as in our patient. The opposite is true for the posterior subtype. A recent case series consisting of 35 patients reported a higher incidence of anterior PALPA (1), and both types were more common in men. Respiratory symptoms (including shortness of breath, stridor, and pulmonary infections) were statistically higher in patients with posterior PALPA (1). Our patient has the anterior subtype of PALPA.

PALPA should not be confused with an aberrant left PA, with or without a sling, in which the entire left PA arises off the right PA. An aberrant left PA with a sling is characterized by the left PA arising from the right PA while coursing between the trachea and esophagus to reach the left lung, thus forming a sling which may lead to airway compression.

Keywords: CT Angiography, Vascular, Thorax, Pulmonary Arteries