Reconsideration of the anatomy of sling left pulmonary artery: the association of one form with bridging bronchus and imperforate anus. Anatomic and diagnostic aspects.

In sling (retrotracheal) left pulmonary artery (SLPA), the tracheobronchial pattern is generally considered basically normal. Analysis of dissected specimens and/or bronchograms and other preparations from five studied and 32 reported patients suggests that there are two different forms of SLPA: (1) types 1A and B, with normal TB pattern [with (A) or without (B) a right pre-eparterial (tracheal bronchus)], and the aberrant left pulmonary artery causing TB compression. The tracheal bifurcation in type 1 SLPA is usually demonstrable at the fourth to fifth thoracic vertebral level; (2A) SLPA type 2A, with bridging bronchus (BB), in which condition the right main bronchus supplies the right upper lobe, but the bronchus supplying the right middle and lower lobes (the bridging bronchus) arises from the left main bronchus (LMB), posterior to which the SLPA courses; (2B) SLPA type 2B, with absence of the right bronchial tree, and the right lung (usually hypoplastic) supplied by a BB from the LMB, posterior to which the SLPA courses. SLPA types 2A and B have in common varying degrees of tracheal stenosis with abnormal cartilage rings and absent tracheal pars membranacea, abnormally low tracheal "bifurcation" (pseudocarina) at average level T6, increased bronchial angles with "inverted T" pattern, and lower level of anterior esophageal indentation by the SLPA than SLPA type 1. Imperforate anus occurred in 8/58 (14%) of patients with SLPA types 2A or B, but possibly in none with SLPA type 1. SLPA type 2 is the predominant form of SLPA, with the incidence of type 2B being twice that of type 2A.(ABSTRACT TRUNCATED AT 250 WORDS)