A case description of tracheobronchomegaly combined with bronchiectasis and infection

Introduction

Tracheobronchomegaly (TBM), also known as Mounier-Kuhn syndrome (MKS), is a rare congenital disease, more common in male patients aged 30–50 years, characterized by dilation of the trachea and main branch lumens (1). The pathological changes in TBM include atrophy of elastic fibers and smooth muscle tissue of the trachea and main bronchus. Bronchiectasis primarily arises from acute or chronic respiratory tract infections or conditions such as bronchial obstruction. This leads to recurrent inflammation within the bronchi, structural damage to the bronchial walls, and a series of issues, culminating in abnormal and persistent bronchial dilation. Therefore, although both TBM and bronchiectasis involve airway dilation, their pathogenic mechanisms differ. TBM is primarily a congenital condition, and unlike acquired bronchiectasis, it is not associated with factors such as chronic inflammation and infection of the trachea and bronchi. However, patients with TBM often coexist with or predispose to bronchiectasis. This article reports the imaging findings of a patient with TBM complicated with bronchiectasis and infection.

Case presentation

A 34-year-old man presented with cough and expectoration for three days and had dyspnea one day earlier. Three days ago, the patient had developed cough and sputum after catching a cold; the sputum was yellow, white, and sticky; the patient did not have fever, chills, or dyspnea, and his symptoms were not obvious after self-medication treatment. One day prior, the patient had developed dyspnea and other discomfort in addition to the above symptoms, prompting him to visit the hospital.

Auscultation detected breathing sounds in both lungs that were coarse and accompanied with a slight dryness or wetness.

The results of the blood routine analysis were as follows: monocyte percentage 11.7%, neutrophil 1.7×10⁹/L, alanine aminotransferase 55 U/L, total protein 64 g/L. Meanwhile, sputum culture revealed gram-positive cocci and gram-negative cocci. In the patient’s chest computed tomography (CT) examination, multiple bronchiectasis and multiple mucus emboli were observed in both lungs, and mild emphysema was observed in both lungs. At the same time, there were several small nodules detected in the anterior segment of the upper lobe, lateral segment of the middle lobe, and outer basal segment of the lower lobe of the right lung, which were considered inflammatory changes. Pulmonary bronchiectasis was shown in the patient’s subsequent fiberoptic bronchoscopy (FOB).

After administering anti-inflammatory, antispasmodic, expectorant, and phlegm-resolving medications, as well as performing FOB suction treatment, the patient’s condition improved, and he were discharged from the hospital. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration (as revised in 2013). Written informed consent was provided by the patient for publication of this article and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Discussion

TBM, also known as MKS, is a rare disease. The first case was described in 1932 (1). Due to its association with Ehlers Danlos syndrome and childhood skin laxity, most scholars believe that TBM may be a congenital disease characterized by autosomal recessive inheritance (2). The clinical features are not distinctive, exhibiting a range of presentations. Certain individuals may show no symptoms, maintaining regular respiratory function, whereas others might endure persistent coughing, produce sputum regularly, and experience repeated lower respiratory tract infections. In rare cases, a subset of patients might progress to severe respiratory failure, potentially leading to fatal outcomes (3). Due to the rarity and high risk of misdiagnosis of this disease, imaging examination is crucial. In adults, the CT diagnostic criteria are tracheal diameters >30 mm, and main bronchi diameters of >24 and 23 mm for right and left, respectively. An increase in tracheal cross-sectional area beyond 371 mm² in men and 299 mm² in women also defines the disease (3).

The following findings on chest CT may help to diagnose of TBM: 2 mm above the tracheal carina, the transverse coronal diameter of the trachea is 44.5 mm, the maximum diameter of the trachea is 30.4 mm, the diameter of the right main bronchus is 25.2 mm, and the diameter of the left main bronchus is 20.0 mm (Figure 1). In the three-dimensional reconstruction of the CT scan, it can be observed that the trachea to the bronchus and the distant airway are gradually widened and there is diffuse dilatation of the bronchi. At the same time, the mucosal uplift inside the air duct wall leads to the change of the air duct wall wave (Figure 2). The diagnostic criteria on chest lateral X-ray are tracheal diameter ≥30 mm, right main bronchus diameter ≥24 mm, and left main bronchus diameter ≥23 mm (5). Meanwhile, CT scanning is highly sensitive to the respiratory cycle during image acquisition, thus the difference in diameter between bronchi during inhalation and exhalation also contributes to the diagnosis of the disease. However, we have not conducted such scans yet, which is a drawback on our part. The main feature of chest X-ray is the fan-shaped tracheal contour formed by mucosal protrusion between cartilage rings, visible in front of the lateral projection, as well as the tracheal diverticulum and bronchiectasis endangering the central bronchus (6). In this case, the patient’s trachea was markedly dilated, but no significant diverticula formation was observed (Figure 3). However, TBM is more likely to be missed on an X-ray than on a CT scan because the images on the X-ray are not apparent in some patients. Bronchoscopy continues to serve as a robust diagnostic modality capable of identifying the expansion of the trachea and main bronchi during inhalation, as well as their constriction and potential collapse during exhalation and coughing (7). During FOB examination, patients with TBM typically exhibit the absence of tracheal cartilage rings, resulting in abnormal widening and collapse of the airways. Additionally, mucosal thinning and dilation of multiple bronchi can be observed (Figure 4).

Figure 1 Thoracic CT scan. (A) The transverse coronal diameter of the trachea is 44.5 mm; the sagittal diameter of the trachea is 29.3 mm; (B) multiple bronchiectasis in both lungs (red arrows); increased middle lobe density in the right lung (blue arrow). CT, computed tomography.

Figure 2 Three-dimensional reconstruction of CT scan: the trachea is enlarged, and the tracheal wall exhibits undulating changes. The different colors of the trachea represent the semiquantitatively encoded diameters (purple indicating the largest, whereas yellow-red indicates the smallest) (4). CT, computed tomography.

Figure 3 Frontal and lateral chest X-ray. (A) Tracheal dilation is faintly visible; (B) the trachea is significantly dilated (red arrow).

Figure 4 Bronchoscopy. (A) Bilateral bronchial dilatation and mucosal atrophy; (B) the normal tracheal cartilage rings are absent, and the diameter of the airway increases significantly with a flattened lumen (the red arrows represent the tracheal cartilage rings that have lost their normal structure).

TBM frequently leads to bronchiectasis, bullous emphysema, recurrent pneumonia, and aspergillosis, which are the predominant pulmonary complications associated with this condition (8). Some researchers have suggested that the pathological alterations seen in TBM within the primary airway might not confine themselves solely to the immediate airway region. Instead, these changes could potentially extend further into the distant airway, subsequently leading to the development of bronchiectasis (9). Since TBM often accompanies bronchiectasis, and both conditions exhibit similar radiological features, such as “orbital sign” and “signet ring sign”, it is imperative to pay closer attention to distinguishing between these two diseases. One approach to differentiation is by considering the segments of the bronchi affected by the disease: TBM mainly affects the trachea, left and right main bronchi, whereas bronchiectasis mainly affects segmental and subsegmental bronchi.

There is no particular remedy for TBM, and asymptomatic patients do not need treatment. Smoking cessation helps to delay the progression of the disease. Treatment for symptomatic patients mainly aims to prevent recurrent respiratory infections and can be managed with bronchodilators, antibiotics, chest physiotherapy, and postural drainage (10).

Conclusions

TBM is very rare in clinical practice, and its clinical manifestations lack specificity. Through the utilization of imaging techniques, particularly CT scans, the visualization and determination of airway dimensions have significantly improved, aiding in the identification of clear abnormalities. However, due to the lack of routine airway measurements in clinical diagnosis, many patients who have slightly exceeded the established normal upper limit have been overlooked (11). Thus, if doctors have insufficient understanding of the disease, missed diagnosis or misdiagnosis can easily occur. Therefore, doctors should take extra care when diagnosing suspicious patients. Bronchoscopy examination can be combined with imaging examination to help doctors make a more definite diagnosis, thus providing better treatment for patients as early as possible and improving their prognosis.

Acknowledgments

Funding: None.

Footnote

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-24-41/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration (as revised in 2013). Written informed consent was provided by the patient for publication of this article and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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