paratracheal air cyst frequency in patients referred to multidetector computed tomography (mdct) unit of alzahra hospital, isfahan, iran, in 2012-2013

background: paratracheal air cysts (pacs) are extraluminal collections of air mostly located adjacent to the right of the trachea at the level of the thoracic inlet. although, pacs are usually asymptomatic, the lesions do occasionally cause complications such as chronic cough, difficult intubation, and right-sided recurrent laryngeal nerve palsy. the purpose of the present study was to demonstrate the appearance and prevalence of pacs through retrospective review of multidetector computed tomography (mdct) of the chest. methods: in a cross sectional study, a total of 1054 chest mdct scans of patients that referred to mdct unit of alzahra hospital in isfahan, iran, from 2012 to 2013 were reviewed. exclusion criteria were history of thoracic surgery, history of tracheostomy or tracheal intubation and presence of tracheal lesions. pacs were evaluated for size and the presence of visible communication with the trachea. patient demographics, age and sex were also collected. findings: of the 1054 patients evaluated, 112 (10.6%) of them had pacs. 103 (92%) patients had one pac, and 9(8%) had two pacs. age of the patients ranged from 6 to 91 years. in 43 (38.4%) of the patients, a direct communication with the trachea was seen. sizes of the pacs ranged from 1 mm to 13.1 mm with mean ± sd 3.89 ± 2.72 mm. pacs were < 5 mm, 5-10 mm, and > 10 mm, in 86 (76%), 21 (20%), and 5 (4%) of the patients, respectively. pacs which had communication with trachea, were significantly larger than the cysts without communication (p = 0.01). conclusion: pac is a common finding on ct examinations of the chest that occur in an expectable location. the exact pathogenesis of pac is unclear but presence of these cysts in a wide age range may suggest congenital and acquired causes.