Abstract
Background and Aims:
Gas accumulation around the tracheamay is observed in neck and thoracic CT scans making the radiologist suspect whether these symptoms are associated with a pathologic process. This study was designed to evaluate the prevalence of partharesal cysts and their association with lung disease.
Methods:
The results of 400 patients evaluated for thoracic routine were analyzed for presence of paratracheal cysts. The location of cysts, size, shape and their relationship with the trachea were studied. The patients’ results were compared with and without paratracheal cysts. The collected data were analyzed using SPSS software version 22.
Results:
Paratracheal cysts were found in 30 patients (7.5%) including 12 males and 18 females (P = 0.07). The age range was between 3 to 78 years old and the mean ages in patients with and without paratracheal cysts were 54 and 38 years, respectively (P < 0.0001). More than 60% of patients had cysts associated with the trachea. The mean AP level in patients with paratracheal cysts was significantly higher (P = 0.04). In addition, it was observed that the incidence of paratracheal cysts in patients with lung disease and especially COPD patients was higher (P < 0.0001).
Conclusion:
In general, the results of this study showed that paratracheal cysts had a high prevalence and had a significant correlation with the presence of COPD. It was also observed that the incidence of these cysts increases in older people, which indicates that paratracheal cysts have an acquired mechanism.
Keywords: Lung disease, multi-detector CT scan, paratracheal cyst
Introduction
Paratracheal air cysts (PACs) are cystic lesions containing air found in the upper, posterior, and right side of the trachea at the chest inlet.[1,2,3] These lesions are randomly found in chest radiographs and in a small number of chest, neck and vertebra CT scans[1,2] and can be associated with chronic cough and chronic obstructive pulmonary disease (COPD).[3] It has been shown in many studies that paratracheal air cysts are a kind of trachea diverticulitis due to their relationship with the trachea lumen, which is more common in the chest inlet and the right side, behind the trachea tube and on the T2 vertebrae. Most of the patients are asymptomatic,[1,2,4] but as they can be a reservoir for the accumulation of secretions, they can lead to frequent infections.[3] Trachea diverticulum is often due to trachea mucus sprouting into the wall weaknesses due to increased chest pressure.[3] Histological findings indicate that the paratracheal air cysts are covered by cylindrical epithelial tissue and are often associated with the trachea lumen.[3,4] Pathologic diagnoses in patients with paratracheal air cysts that have been surgically approved include trachea diverticulum, lymphopyteliol cysts and bronchogenic cysts.[3] In the differential diagnosis of parathyroid cysts, cases such as laryngocele, pharyngoceles, zenker diverticulum, lung herniation, mediastinum air and upper paraspotal lung bulbs have been suggested that can be mistaken in diagnosis of paratracheal air cysts.[3]
CT scans can be used to diagnose paratracheal air cysts in addition to their location – the upper, posterior and right side of the trachea-distance from the pleura, the connection with the trachea and its round margin. However, bronchoscopy also helps in detecting it. The treatment of this condition is usually surgery.
Previous studies have shown that there is a relationship between paratracheal air cysts and obstructive lung disease and lung emphysema, bronchiectasis, pneumothorax, bola and sternotomy,[1,2] due to weakness in the right wall and back of the trachea, the reason of which is the increased pressure in this part. These cysts are mostly asymptomatic, but in a few cases, they cause chronic coughing and other problems such as intubation and recurrent laryngeal nerve palsy. Moreover, the presence of these cysts in people with trauma is confused with mediastinum air.
There are limited studies that show the association of paratracheal air cysts with COPD, emphysema and bronchiectasis but the data is very unclear and limited.[3] The present study was designed to investigate the prevalence of paratracheal air cysts and their shape, size, number and relationship with Paranchymal lung disease in neck and thoracic CT scans.
Methods
This cross-sectional epidemiologic study was performed on 400 patients referred to the CT scan department of Ahvaz Golestan Hospital. Patients with mediastinum lesion were excluded. This study was approved by the ethics committee of Jundishapur University of Medical Sciences. Written consent of all patients was received before beginning the study.
Measurements
In this study, demographic data including age, gender, height and weight were recorded. The images of patients undergoing chest and neck CT scan were then examined independently by two radiologists with experience in the field of lung disease. The data were recorded in the data collection form. All images were stored with two standard mediastinum and Paranchymal windows and analyzed in the PACS system of the university.
Statistical analysis
The collected data were analyzed using SPSS software version 22. P < 0.05 was considered as a significant result.
Results
In this study, 400 patients who referred for lung CT scan and presence or absence of paratracheal air cysts were evaluated. The association between incidence of these cysts and underlying lung diseases was also assessed. Based on the results, 30 patients, including 18 women and 12 men had paratracheal air cysts and the incidence of paratracheal cysts in these patients was 7.5%.
The mean age of patients with paratracheal cysts was 54.9 years. The average size of these cysts was 7.45 mm. In terms of underlying illness, 22 had lung disease and 8 others had normal lungs.
The association of paratracheal air cysts with various Paranchymal lung diseases is shown in Table 1. Based on this result, it was found that there is a significant relationship between the incidence of cyst and the presence of lung diseases. In addition, the relationship between the shape and location of paratracheal air cysts with different Paranchymal lung diseases was not statistically significant.
Table 1.
Relationship between incidence of cysts and lung diseases
| Groups | Group | P | ||
|---|---|---|---|---|
| Control (n=370) | Cases (n=30) | |||
| None | Count | 270 | 8 | X2=177.46, |
| % within Sysdis | 97.1% | 2.9% | df=11, P<0.0001 | |
| % within Group | 73.0% | 26.7% | ||
| Pulmonary | Count | 16 | 2 | |
| Edema | % within Sysdis | 88.9% | 11.1% | |
| % within Group | 4.3% | 6.7% | ||
| COPD | Count | 0 | 7 | |
| % within Sysdis | 0.0% | 100.0% | ||
| % within Group | 0.0% | 23.3% | ||
| Emphysma | Count | 10 | 3 | |
| % within Sysdis | 76.9% | 23.1% | ||
| % within Group | 2.7% | 10.0% | ||
| Upper lobe brochectasia | Count | 0 | 5 | |
| % within Sysdis | 0.0% | 100.0% | ||
| % within Group | 0.0% | 16.7% | ||
| Penuminia | Count | 33 | 3 | |
| % within Sysdis | 91.7% | 8.3% | ||
| % within Group | 8.9% | 10.0% | ||
| Fibrosis | Count | 5 | 1 | |
| % within Sysdis | 83.3% | 16.7% | ||
| % within Group | 1.4% | 3.3% | ||
| Lung Cancer | Count | 0 | 1 | |
| % within Sysdis | 0.0% | 100.0% | ||
| % within Group | 0.0% | 3.3% | ||
| Phunemothorax | Count | 21 | 0 | |
| % within Sysdis | 100.0% | 0.0% | ||
| % within Group | 5.7% | 0.0% | ||
| ARDS | Count | 5 | 0 | |
| % within Sysdis | 100.0% | 0.0% | ||
| % within Group | 1.4% | 0.0% | ||
| Plural Efusion | Count | 5 | 0 | |
| % within Sysdis | 100.0% | 0.0% | ||
| % within Group | 1.4% | 0.0% | ||
| Pulmonary cysts | Count | 5 | 0 | |
| % within Sysdis | 100.0% | 0.0% | ||
| % within Group | 1.4% | 0.0% | ||
The relationship between gender and paratracheal air cysts in the subjects is presented in Table 2. Based on this assessment, although the incidence of paratracheal air cysts was higher in women, this difference was not statistically significant (P = 0.071).
Table 2.
Relationship between gender and the presence of paratracheal air cysts
| Groups | Group | Total | P | |||
|---|---|---|---|---|---|---|
| Control | Cases | |||||
| Gender | Male | Count | 206 | 12 | 218 | X2=2.7, df=1, |
| % within Gender | 94.5% | 5.5% | 100.0% | P=0.071 | ||
| % within Group | 55.7% | 40.0% | 54.5% | |||
| Female | Count | 164 | 18 | 182 | ||
| % within Gender | 90.1% | 9.9% | 100.0% | |||
| % within Group | 44.3% | 60.0% | 45.5% | |||
In addition, the mean size of paratracheal air cysts in different Paranchymal lung diseases was evaluated and it was found that its largest size was observed in patients with COPD and then upper lobe bronchiectasis. Besides, based on variance analysis, it was found that the difference in size was statistically significant in different diseases [Table 3]. The mean diameter of anterior posterior chest wall was significantly higher in patients with paratracheal air cysts (P = 0.043).
Table 3.
Relationship between lung disease and paratracheal air cysts’ size
| Diseases | n | Mean | Std. Deviation | Std. Error | 95% Confidence Interval for Mean | Minimum | Maximum | P | |
|---|---|---|---|---|---|---|---|---|---|
| Lower Bound | Upper Bound | ||||||||
| none | 8 | 5.0000 | 1.51186 | 0.53452 | 3.7361 | 6.2639 | 3.00 | 7.00 | P<0.0001 |
| Pulmonary Edema | 2 | 4.0000 | 1.41421 | 1.00000 | -8.7062 | 16.7062 | 3.00 | 5.00 | |
| COPD | 7 | 10.6429 | 2.98209 | 1.12712 | 7.8849 | 13.4008 | 4.50 | 14.00 | |
| Emphysma | 3 | 9.3333 | 2.08167 | 1.20185 | 4.1622 | 14.5045 | 7.00 | 11.00 | |
| Upper lobe brochectasia | 5 | 10.2000 | 2.68328 | 1.20000 | 6.8683 | 13.5317 | 6.00 | 13.00 | |
| Penuminia | 3 | 3.8333 | 0.76376 | 0.44096 | 1.9360 | 5.7306 | 3.00 | 4.50 | |
| Fibrosis | 1 | 3.5000 | . | . | . | . | 3.50 | 3.50 | |
| Lung Cancer | 1 | 7.0000 | . | . | . | . | 7.00 | 7.00 | |
| Total | 30 | 7.4500 | 3.50701 | 0.64029 | 6.1405 | 8.7595 | 3.00 | 14.00 | |
Moreover, the mean age of these patients was significantly different from those in the control group [Table 4].
Table 4.
Comparison of mean age and anterior posterior diameter of the chest wall in patients with and without paratracheal air cysts
| Group | n | Mean | Std. Deviation | Std. Error Mean | P | |
|---|---|---|---|---|---|---|
| Age | Control | 370 | 38.9378 | 18.43612 | 0.95845 | P<0.0001 |
| Cases | 30 | 54.9333 | 12.03424 | 2.19714 | ||
| AP | Control | 365 | 171.8356 | 11.47670 | 0.60072 | P=0.043 |
| Cases | 30 | 177.0667 | 28.88853 | 5.27430 |
Discussion
Paratracheal air cysts that accumulate near the trachea are usually asymptomatic and considered as a random result. These cysts are usually associated with the trachea and may be seen as single or multi-hole. Previous studies have suggested that paratracheal cysts are initially located on inner surface of the chest along the lateral posterior side of the trachea.[5,6]
In early studies in the 1950s by MacKinnon, the prevalence of this cyst was evaluated by autopsy and the prevalence was reported as 1%. However, with the advent of advanced imaging methods, more studies have been done on this subject and its prevalence has been reported in CT-scan studies ranging from 0.3 to 6.5 percent.[6,7,8] In the current study, the prevalence of paratracheal cysts was 7.5%. In a similar study conducted on 1027 patients, Boyaci et al. reported an incidence of 8% in paratracheal cysts.[9] Baei et al. also reported the rate of 8.1%, which is slightly higher than the results of the present study.[10] This increase is likely to be due to the use of high-resolution CT scans and low thickness of pieces. In this study, the 1 mm thick pieces were used. On the other hand, the prevalence of paratracheal cysts in the Kim and Polat studies was 6.8 and 4% respectively.[11,12] Similarly, the reduced incidence in these studies may also be due to the use of thicker pieces.
The etiology of paratracheal cysts has not yet been well established; Goo et al. have suggested that these cysts are likely to be caused by trachea mucus sprout through weak trachea points due to chronic inflammation or increased intra-luminal pressure.[5] Previous studies have shown that paratracheal cysts are located on the right side of the trachea.[11,12,13,14] The current study also showed that most of these cysts were seen on the right side and were only seen on the left in just one case. Given that the esophagus and the aortic arch are usually located on the left side of the trachea, the right side is weaker against intratracheal pressure and this probably justifies the reported findings.[8,9,12] The amount of tracheal associated cysts varied in different studies and ranged from 31.5[11] to 56.1%.[9] In the present study, this figure was more than 63%. This is probably due to differences in the resolution of the devices used in the study.
The female population showed a higher percentage of tracheal cysts. In this regard, past studies have also shown that paratracheal cysts are more prevalent in women.[9,10] The mean age of the patients in this study was 55 years. Therefore, it seems that its prevalence peak is in the fifth to sixth decades. In line with these results, many previous studies have also shown that the sixth decade of life is the peak of paratracheal cysts’ prevalence.[9,10,12] In the present study, patients with paratracheal cysts were significantly older. Therefore the underlying mechanism for creating these cysts should be acquired.
Many researchers have reported that bronchial diverticulum associated with COPD and lung disease is due to cigarette smoking.[15,16,17,18] However, these connections are still controversial and need to be further explored. Goo et al.[5] and Polat et al.[12] reported that the presence of paratracheal cysts indicates the presence of obstructive lung disease and possibly emphysema. In addition, Boyaci et al. suggested that the presence of paratracheal cysts has a significant relationship with bronchiectasis.[9] A recent study also showed a significant relationship between upper lobe fibrosis and the incidence of paratracheal cysts.[19] In the present study, it was found that the prevalence of paratracheal air cysts was significantly associated with the presence of underlying lung diseases. In complementary evaluations, it was found that COPD specifically increases the incidence of paratracheal cysts.
The evaluation of the prevalence of paratracheal cysts in relation to Paranchymal lung diseases for the first time was among the innovations of this study. Another strength point of this study was to determine the relationship between air cysts and lung diseases.
Conclusion
In general, the results of this study indicate that paratracheal cysts have a significant relationship with the presence of COPD disease. The incidence of these cysts increases in older ages indicating that paratracheal cysts have an acquired mechanism.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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